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Optimize multiplexers in Dfg synthesis (#6331) 

The previous algorithm was designed to handle the general case where a
full control flow path predicate is required to select which value to
use when synthesizing control flow join point in an always block.

Here we add a better algorithm that tries to use the predicate of
the closest dominating branch if the branch paths dominate the joining
paths. This is almost universally true in synthesizable logic (RTLMeter
has no exceptions), however there are cases where this is not
applicable, for which we fall back on the previous generic algorithm.

Overall this significantly simplifies the synthesized Dfg graphs and
enables further optimization.
This commit is contained in:
Geza Lore 2025-08-25 13:47:45 +01:00 committed by GitHub
parent c2cac8a7fd
commit 02e64f0795
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
12 changed files with 1269 additions and 407 deletions
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287
src/V3Cfg.cpp
View File

@ -29,24 +29,9 @@
VL_DEFINE_DEBUG_FUNCTIONS;
//######################################################################
// ControlFlowGraph method definitions
// CfgBlock method definitions
bool ControlFlowGraph::containsLoop() const {
for (const V3GraphVertex& vtx : vertices()) {
const BasicBlock& current = static_cast<const BasicBlock&>(vtx);
for (const V3GraphEdge& edge : current.outEdges()) {
const BasicBlock& successor = *static_cast<const BasicBlock*>(edge.top());
// IDs are the reverse post-order numbering, so easy to check for a back-edge
if (successor.id() < current.id()) return true;
}
}
return false;
}
//######################################################################
// BasicBlock method definitions
std::string BasicBlock::name() const {
std::string CfgBlock::name() const {
std::stringstream ss;
ss << "BB " + std::to_string(id()) + ":\n";
for (AstNode* nodep : m_stmtps) {
@ -62,25 +47,25 @@ std::string BasicBlock::name() const {
V3EmitV::debugVerilogForTree(nodep, ss);
}
}
std::string text = VString::replaceSubstr(ss.str(), "\n", "\\l ");
if (inEmpty()) text = "**ENTER**\n" + text;
if (outEmpty()) text = text + "\n**EXIT**";
std::string text = VString::replaceSubstr(
VString::replaceSubstr(ss.str(), "\n", "\\l "), "\"", "\\\"");
if (isEnter()) text = "**ENTER**\n" + text;
if (isExit()) text = text + "\n**EXIT**";
return text;
}
std::string BasicBlock::dotShape() const { return "rect"; }
std::string BasicBlock::dotRank() const {
if (inEmpty()) return "source";
if (outEmpty()) return "sink";
std::string CfgBlock::dotShape() const { return "rect"; }
std::string CfgBlock::dotRank() const {
if (isEnter()) return "source";
if (isExit()) return "sink";
return "";
}
//######################################################################
// ControlFlowEdge method definitions
// CfgEdge method definitions
std::string ControlFlowEdge::dotLabel() const {
std::string CfgEdge::dotLabel() const {
std::string label = "E" + std::to_string(id());
const BasicBlock& source = *fromp()->as<BasicBlock>();
const ControlFlowEdge* const untknp = source.untknEdgep();
const CfgEdge* const untknp = srcp()->untknEdgep();
if (this == untknp) {
label += " / F";
} else if (untknp) {
@ -88,3 +73,249 @@ std::string ControlFlowEdge::dotLabel() const {
}
return label;
}
//######################################################################
// CfgGraph method definitions
static void cfgOrderVisitBlock(std::vector<CfgBlock*>& postOrderEnumeration, CfgBlock* bbp) {
// Mark visited
bbp->user(1);
// Visit un-visited successors
if (CfgBlock* const takenp = bbp->takenp()) {
if (!takenp->user()) cfgOrderVisitBlock(postOrderEnumeration, takenp);
if (CfgBlock* const untknp = bbp->untknp()) {
if (!untknp->user()) cfgOrderVisitBlock(postOrderEnumeration, untknp);
}
}
// Add to post order enumeration
postOrderEnumeration.emplace_back(bbp);
};
void CfgGraph::rpoBlocks() {
UASSERT_OBJ(m_nEdits != m_nLastOrdered, m_enterp, "Redundant 'CfgGraph::order' call");
m_nLastOrdered = m_nEdits;
// Reset marks
for (V3GraphVertex& v : vertices()) v.user(0);
// Compute post-order enumeration. Simple recursive algorith will do.
std::vector<CfgBlock*> postOrderEnumeration;
postOrderEnumeration.reserve(m_nBlocks);
cfgOrderVisitBlock(postOrderEnumeration, m_enterp);
UASSERT_OBJ(postOrderEnumeration.size() == m_nBlocks, m_enterp, "Inconsistent block count");
// Assign block IDs equal to the reverse post-order number and sort vertices
for (size_t i = 0; i < postOrderEnumeration.size(); ++i) {
CfgBlock* const bbp = postOrderEnumeration[m_nBlocks - 1 - i];
bbp->m_rpoNumber = i;
vertices().unlink(bbp);
vertices().linkBack(bbp);
}
// Assign edge IDs
size_t edgeCount = 0;
for (V3GraphVertex& v : vertices()) {
for (V3GraphEdge& e : v.outEdges()) static_cast<CfgEdge&>(e).m_id = edgeCount++;
}
UASSERT_OBJ(edgeCount == m_nEdges, m_enterp, "Inconsistent edge count");
}
bool CfgGraph::containsLoop() const {
for (const V3GraphVertex& vtx : vertices()) {
const CfgBlock& current = static_cast<const CfgBlock&>(vtx);
for (const V3GraphEdge& edge : current.outEdges()) {
const CfgBlock& successor = *static_cast<const CfgBlock*>(edge.top());
// IDs are the reverse post-order numbering, so easy to check for a back-edge
if (successor.id() < current.id()) return true;
}
}
return false;
}
void CfgGraph::minimize() {
// Remove empty blocks (except enter and exit)
for (V3GraphVertex* const vtxp : vertices().unlinkable()) {
CfgBlock* const bbp = static_cast<CfgBlock*>(vtxp);
if (bbp->isEnter()) continue;
if (bbp->isExit()) continue;
if (!bbp->stmtps().empty()) continue;
UASSERT(!bbp->isBranch(), "Empty block should have a single successor");
CfgBlock* const succp = bbp->takenp();
for (V3GraphEdge* const edgep : bbp->inEdges().unlinkable()) edgep->relinkTop(succp);
++m_nEdits;
--m_nEdges;
--m_nBlocks;
VL_DO_DANGLING(bbp->unlinkDelete(this), bbp);
}
// Combine sequential blocks
for (V3GraphVertex* const vtxp : vertices().unlinkable()) {
CfgBlock* const srcp = static_cast<CfgBlock*>(vtxp);
if (srcp->isExit()) continue;
if (srcp->isBranch()) continue;
CfgBlock* const dstp = srcp->takenp();
if (dstp->isJoin()) continue;
// Combine them
if (srcp->isEnter()) m_enterp = dstp;
std::vector<AstNodeStmt*> stmtps{std::move(srcp->m_stmtps)};
stmtps.reserve(stmtps.size() + dstp->m_stmtps.size());
stmtps.insert(stmtps.end(), dstp->m_stmtps.begin(), dstp->m_stmtps.end());
dstp->m_stmtps = std::move(stmtps);
for (V3GraphEdge* const edgep : srcp->inEdges().unlinkable()) edgep->relinkTop(dstp);
++m_nEdits;
--m_nEdges;
--m_nBlocks;
VL_DO_DANGLING(srcp->unlinkDelete(this), srcp);
}
if (m_nEdits != m_nLastOrdered) rpoBlocks();
if (dumpGraphLevel() >= 9) dumpDotFilePrefixed("cfg-minimize");
}
void CfgGraph::breakCriticalEdges() {
// Gather critical edges
std::vector<CfgEdge*> criticalEdges;
criticalEdges.reserve(m_nEdges);
for (V3GraphVertex& vtx : vertices()) {
const CfgBlock& bb = static_cast<const CfgBlock&>(vtx);
if (!bb.isBranch()) continue;
for (V3GraphEdge& edge : vtx.outEdges()) {
const CfgBlock& succ = static_cast<const CfgBlock&>(*edge.top());
if (!succ.isJoin()) continue;
criticalEdges.emplace_back(static_cast<CfgEdge*>(&edge));
}
}
// Insert blocks
for (CfgEdge* const edgep : criticalEdges) {
CfgBlock* const newp = addBlock();
addTakenEdge(newp, edgep->dstp());
edgep->relinkTop(newp);
}
if (m_nEdits != m_nLastOrdered) rpoBlocks();
if (dumpGraphLevel() >= 9) dumpDotFilePrefixed("cfg-breakCriticalEdges");
}
// Given a branching basic block, if the sub-graph below this branch, up until
// the point where all of its control flow path convertes is series-parallel,
// then return the (potentially newly created) basic block with exactly 2
// predecessors where the two control flow paths from this branch have joined.
// If the relevant sub-graph is not series-parallel (there is a control flow
// path between the branches, or to a path not dominated by the given branch),
// then return nullptr. Cached results in the given map
CfgBlock* CfgGraph::getOrCreateTwoWayJoinFor(CfgBlock* bbp) {
UASSERT_OBJ(bbp->isBranch(), bbp, "Not a branch");
// Mark visited
UASSERT_OBJ(!bbp->user(), bbp, "Should not visit twice");
bbp->user(1);
// We need the edge converting to a join block along both path. This is how we find it:
const auto chaseEdge = [&](CfgEdge* edgep) -> CfgEdge* {
while (true) {
CfgBlock* dstp = edgep->dstp();
// Stop if found the joining block along this path
if (dstp->isJoin()) return edgep;
// If the successor is a branch, recursively get it's 2-way join block
while (dstp->isBranch()) {
dstp = getOrCreateTwoWayJoinFor(dstp);
// If the subgarph below dstp is not series-parallel, then no solution
if (!dstp) return nullptr;
}
UASSERT_OBJ(!dstp->isExit(), bbp, "Non-convergent branch - multiple Exit blocks?");
edgep = dstp->takenEdgep();
}
};
// Walk down both paths
CfgEdge* const takenEdgep = chaseEdge(bbp->takenEdgep());
if (!takenEdgep) return nullptr;
CfgEdge* const untknEdgep = chaseEdge(bbp->untknEdgep());
if (!untknEdgep) return nullptr;
// If we ended up at different joining blocks, then there is a path from one
// of the branches into a path of another branch before 'bbp', no solution
if (takenEdgep->dstp() != untknEdgep->dstp()) return nullptr;
// Pick up the common successor
CfgBlock* const succp = takenEdgep->dstp();
// If the common successor is a 2-way join, we can use it directly
if (succp->isTwoWayJoin()) return succp;
// Otherwise insert a new block to join the 2 paths of the original block
CfgBlock* const joinp = addBlock();
addTakenEdge(joinp, succp);
takenEdgep->relinkTop(joinp);
untknEdgep->relinkTop(joinp);
return joinp;
}
bool CfgGraph::insertTwoWayJoins() {
// Reset marks
for (V3GraphVertex& v : vertices()) v.user(0);
bool isSeriesParallel = true;
// We will be adding vertices at the end. That's OK, they don't need to be visited again
for (V3GraphVertex& v : vertices()) {
CfgBlock& bb = static_cast<CfgBlock&>(v);
// Skip if already visited
if (bb.user()) continue;
// Skip if not a branch
if (!bb.isBranch()) continue;
// Fix it up, record if failed
if (!getOrCreateTwoWayJoinFor(&bb)) isSeriesParallel = false;
}
if (m_nEdits != m_nLastOrdered) rpoBlocks();
if (dumpGraphLevel() >= 9) dumpDotFilePrefixed("cfg-insertTwoWayJoins");
return isSeriesParallel;
}
//######################################################################
// CfgDominatorTree
const CfgBlock* CfgDominatorTree::intersect(const CfgBlock* ap, const CfgBlock* bp) {
while (ap != bp) {
while (*ap > *bp) ap = m_bb2Idom[*ap];
while (*bp > *ap) bp = m_bb2Idom[*bp];
}
return ap;
}
CfgDominatorTree::CfgDominatorTree(const CfgGraph& cfg)
: m_bb2Idom{cfg.makeBlockMap<const CfgBlock*>()} {
// Build the immediate dominator map, using algorithm from:
// "A Simple, Fast Dominance Algorithm", Keith D. Cooper et al., 2006
// Immediate dominator of the enter block
// Point enteer block to itself, while computing below
m_bb2Idom[cfg.enter()] = &cfg.enter();
// Iterate until settled
for (bool changed = true; changed;) {
changed = false;
// For each vertex except enter block
for (const V3GraphVertex& vtx : cfg.vertices()) {
const CfgBlock& curr = static_cast<const CfgBlock&>(vtx);
if (curr.isEnter()) continue; // Skip entry block
// For each predecessor of current block
const CfgBlock* idom = nullptr;
for (const V3GraphEdge& edge : curr.inEdges()) {
const CfgBlock& pred = static_cast<const CfgBlock&>(*edge.fromp());
// Skip if perdecessor not yet processed
if (!m_bb2Idom[pred]) continue;
// Pick first, then use intersect
idom = !idom ? &pred : intersect(&pred, idom);
}
// If chenged, record it, else move on
if (idom == m_bb2Idom[curr]) continue;
m_bb2Idom[curr] = idom;
changed = true;
}
}
// The enter block is the root of the tree and does not itself have an immediate dominator
m_bb2Idom[cfg.enter()] = nullptr;
}

539
src/V3Cfg.h
View File

@ -68,69 +68,103 @@
#include <vector>
//######################################################################
// DenseMap - This can be made generic if needed
// Control Flow Graph (CFG) and related data structures
// Map from unique non-negative integers (IDs) to generic values. As opposed
// to a std::map/std::unordered_map, in DenseMap, all entries are value
// initialized at construction, and the map is always dense. This can be
// improved if necessary but is sufficient for our current purposes.
template <typename T_Key, size_t (T_Key::*Index)() const, typename T_Value>
class DenseMap final {
std::vector<T_Value> m_map; // The map, stored as a vector
class CfgGraph;
class CfgBlock;
class CfgEdge;
public:
// CONSTRUCTOR
explicit DenseMap(size_t size)
: m_map{size} {}
T_Value& operator[](const T_Key& key) { return m_map.at((key.*Index)()); }
const T_Value& operator[](const T_Key& key) const { return m_map.at((key.*Index)()); }
};
template <typename T_Key, typename T_Value>
class CfgMap;
template <typename T_Value>
class CfgBlockMap;
template <typename T_Value>
class CfgEdgeMap;
//######################################################################
// ControlFlowGraph data structure
// CfgBlock - A basic block (verticies of the control flow graph)
class ControlFlowGraph;
class BasicBlock;
class ControlFlowEdge;
// A basic block (verticies of the control flow graph)
class BasicBlock final : public V3GraphVertex {
VL_RTTI_IMPL(BasicBlock, V3GraphVertex)
class CfgBlock final : public V3GraphVertex {
friend class CfgGraph;
template <typename T_Key, typename T_Value>
friend class CfgMap;
friend class CfgBuilder;
// STATE - Immutable after construction, set by CfgBuilder
// V3GraphEdge::user() is set to the unique id by CfgBuilder
std::vector<AstNodeStmt*> m_stmtps; // statements in this BasicBlock
// STATE
CfgGraph* const m_cfgp; // The control flow graph this CfgBlock is under
size_t m_rpoNumber; // Reverse post-order number and unique ID of this CfgBlock
// CONSTRUCTOR - via CfgBuilder only
inline explicit BasicBlock(ControlFlowGraph* graphp);
~BasicBlock() override = default;
// V3GraphEdge::user() is set to the unique id by CfgBuilder
std::vector<AstNodeStmt*> m_stmtps; // statements in this CfgBlock
// PRIVATE METHODS
// ID (reverse post-order numpber) of this block
inline size_t id();
inline size_t id() const;
// CONSTRUCTOR/DESTRUCTOR - via CfgGraph only
inline explicit CfgBlock(CfgGraph* cfgp);
~CfgBlock() override = default;
public:
// METHODS - all const
// PUBLIC METHODS
// Statements in this BasicBlock
// Is this the entry block of the CFG?
bool isEnter() const { return inEmpty(); }
// Is this the exit block of the CFG?
bool isExit() const { return outEmpty(); }
// Is this a branching block (multiple successors)?
bool isBranch() const { return outEdges().hasMultipleElements(); }
// Is this a control flow convergence block (multiple predecessors)?
bool isJoin() const { return inEdges().hasMultipleElements(); }
// Is this a join of exactly 2 paths?
bool isTwoWayJoin() const { return inEdges().hasTwoElements(); }
// The edge going to the taken (or uncinditional) successor, or nullptr if exit block
inline CfgEdge* takenEdgep();
inline const CfgEdge* takenEdgep() const;
// The edge going to the untaken successor, or nullptr if not a branch, or exit block
inline CfgEdge* untknEdgep();
inline const CfgEdge* untknEdgep() const;
// The taken successor block, or nullptr if exit block
inline CfgBlock* takenp();
inline const CfgBlock* takenp() const;
// The untakens successor block, or nullptr if not a branch, or exit block
inline CfgBlock* untknp();
inline const CfgBlock* untknp() const;
// The first predecessor edge, or nullptr if enter block
inline CfgEdge* firstPredecessorEdgep();
inline const CfgEdge* firstPredecessorEdgep() const;
// The last predecessor edge, or nullptr if enter block
inline CfgEdge* lastPredecessorEdgep();
inline const CfgEdge* lastPredecessorEdgep() const;
// The first predecessor block, or nullptr if enter block
inline CfgBlock* firstPredecessorp();
inline const CfgBlock* firstPredecessorp() const;
// The last predecessor block, or nullptr if enter block
inline CfgBlock* lastPredecessorp();
inline const CfgBlock* lastPredecessorp() const;
// Statements in this CfgBlock
const std::vector<AstNodeStmt*>& stmtps() const { return m_stmtps; }
// Unique ID of this BasicBlock - defines topological ordering
size_t id() const { return V3GraphVertex::user(); }
// The edge corresponding to the terminator branch being taken (including unonditoinal goto)
inline const ControlFlowEdge* takenEdgep() const;
// The edge corresponding to the terminator branch being not taken (or nullptr if goto)
inline const ControlFlowEdge* untknEdgep() const;
// Same as takenpEdgep/untknEdgep but returns the successor basic blocks
inline const BasicBlock* takenSuccessorp() const;
inline const BasicBlock* untknSuccessorp() const;
// Ordering is done on reverese post-order numbering. For loop-free graph
// this ensures that a block that compares less than another is not a
// successor of the other block (it is an ancestor, or sibling).
bool operator<(const CfgBlock& that) const { return id() < that.id(); }
bool operator>(const CfgBlock& that) const { return id() > that.id(); }
bool operator==(const CfgBlock& that) const { return this == &that; }
void forEachSuccessor(std::function<void(const BasicBlock&)> f) const {
for (const V3GraphEdge& edge : outEdges()) f(*edge.top()->as<BasicBlock>());
}
void forEachPredecessor(std::function<void(const BasicBlock&)> f) const {
for (const V3GraphEdge& edge : inEdges()) f(*edge.fromp()->as<BasicBlock>());
// Iterators
void forEachSuccessor(std::function<void(const CfgBlock&)> f) const {
for (const V3GraphEdge& edge : outEdges()) f(*static_cast<CfgBlock*>(edge.top()));
}
void forEachPredecessor(std::function<void(const CfgBlock&)> f) const {
for (const V3GraphEdge& edge : inEdges()) f(*static_cast<CfgBlock*>(edge.fromp()));
}
// Source location for debugging
FileLine* fileline() const override {
return !m_stmtps.empty() ? m_stmtps.front()->fileline() : nullptr;
}
@ -141,130 +175,397 @@ public:
std::string dotRank() const override;
};
// A control flow graph edge
class ControlFlowEdge final : public V3GraphEdge {
VL_RTTI_IMPL(ControlFlowEdge, V3GraphEdge)
friend class CfgBuilder;
//######################################################################
// CfgEdge - An edges of the control flow graph
class CfgEdge final : public V3GraphEdge {
friend class CfgGraph;
template <typename T_Key, typename T_Value>
friend class CfgMap;
// STATE - Immutable after construction, set by CfgBuilder
// V3GraphEdge::user() is set to the unique id by CfgBuilder
CfgGraph* const m_cfgp; // The control flow graph this CfgEdge is under
size_t m_id; // Unique ID of this vertex
// CONSTRUCTOR - via CfgBuilder only
inline ControlFlowEdge(ControlFlowGraph* graphp, BasicBlock* srcp, BasicBlock* dstp);
~ControlFlowEdge() override = default;
// PRIVATE METHODS
// Unique ID of this CfgEdge - no particular meaning
inline size_t id();
inline size_t id() const;
// CONSTRUCTOR/DESTRUCTOR - via CfgGraph only
inline CfgEdge(CfgGraph* graphp, CfgBlock* srcp, CfgBlock* dstp);
~CfgEdge() override = default;
public:
// METHODS - all const
// Unique ID of this ControlFlowEdge - no particular meaning
size_t id() const { return user(); }
// Source/destination BasicBlock
const BasicBlock& src() const { return *static_cast<BasicBlock*>(fromp()); }
const BasicBlock& dst() const { return *static_cast<BasicBlock*>(top()); }
// Source/destination CfgBlock
const CfgBlock* srcp() const { return static_cast<const CfgBlock*>(fromp()); }
const CfgBlock* dstp() const { return static_cast<const CfgBlock*>(top()); }
CfgBlock* srcp() { return static_cast<CfgBlock*>(fromp()); }
CfgBlock* dstp() { return static_cast<CfgBlock*>(top()); }
// For Graphviz dumps only
std::string dotLabel() const override;
};
template <typename T_Value>
using BasicBlockMap = DenseMap<BasicBlock, &BasicBlock::id, T_Value>;
//######################################################################
// CfgGraph - The control flow graph
template <typename T_Value>
using ControlFlowEdgeMap = DenseMap<ControlFlowEdge, &ControlFlowEdge::id, T_Value>;
// The control flow graph
class ControlFlowGraph final : public V3Graph {
class CfgGraph final : public V3Graph {
friend class CfgBlock;
friend class CfgEdge;
template <typename T_Key, typename T_Value>
friend class CfgMap;
friend class CfgBuilder;
// STATE - Immutable after construction, set by CfgBuilder
BasicBlock* m_enterp = nullptr; // The singular entry vertex
BasicBlock* m_exitp = nullptr; // The singular exit vertex
size_t m_nBasicBlocks = 0; // Number of BasicBlocks in this ControlFlowGraph
size_t m_nEdges = 0; // Number of ControlFlowEdges in this ControlFlowGraph
// STATE
size_t m_nEdits = 0; // Edit count of this graph
size_t m_nLastOrdered = 0; // Last edit count blocks were ordered
CfgBlock* m_enterp = nullptr; // The singular entry vertex
CfgBlock* m_exitp = nullptr; // The singular exit vertex
size_t m_nBlocks = 0; // Number of CfgBlocks in this CfgGraph
size_t m_nEdges = 0; // Number of CfgEdges in this CfgGraph
// CONSTRUCTOR - via CfgBuilder only
ControlFlowGraph() = default;
// PRIVATE METHODS
public:
~ControlFlowGraph() override = default;
// Compute reverse post-order enumeration of blocks, and sort them
// accordingly. Assign blocks, and edge IDs. Invalidates all previous IDs.
void rpoBlocks();
// METHODS
void foreach(std::function<void(const BasicBlock&)> f) const {
for (const V3GraphVertex& vtx : vertices()) f(*vtx.as<BasicBlock>());
// Add a new CfgBlock to this graph
CfgBlock* addBlock() {
++m_nEdits;
++m_nBlocks;
return new CfgBlock{this};
}
// Add a new taken (or unconditional) CfgEdge to this CFG
void addTakenEdge(CfgBlock* srcp, CfgBlock* dstp) {
UASSERT_OBJ(srcp->m_cfgp == this, srcp, "'srcp' is not in this graph");
UASSERT_OBJ(dstp->m_cfgp == this, dstp, "'dstp' is not in this graph");
UASSERT_OBJ(!srcp->takenEdgep(), srcp, "Taken edge should be added first");
//
UASSERT_OBJ(dstp != m_enterp, dstp, "Enter block cannot have a predecessor");
UASSERT_OBJ(srcp != m_exitp, srcp, "Exit block cannot have a successor");
++m_nEdits;
++m_nEdges;
new CfgEdge{this, srcp, dstp};
}
// Add a new untaken CfgEdge to this CFG
void addUntknEdge(CfgBlock* srcp, CfgBlock* dstp) {
UASSERT_OBJ(srcp->m_cfgp == this, srcp, "'srcp' is not in this graph");
UASSERT_OBJ(dstp->m_cfgp == this, dstp, "'dstp' is not in this graph");
UASSERT_OBJ(srcp->takenEdgep(), srcp, "Untaken edge shold be added second");
UASSERT_OBJ(srcp->takenp() != dstp, srcp, "Untaken branch targets the same block");
//
UASSERT_OBJ(dstp != m_enterp, dstp, "Enter block cannot have a predecessor");
UASSERT_OBJ(srcp != m_exitp, srcp, "Exit block cannot have a successor");
++m_nEdits;
++m_nEdges;
new CfgEdge{this, srcp, dstp};
}
size_t idOf(const CfgBlock* bbp) const {
UASSERT_OBJ(m_nEdits == m_nLastOrdered, m_enterp, "Cfg was edited but not re-ordered");
return bbp->m_rpoNumber;
}
size_t idOf(const CfgEdge* edgep) const {
UASSERT_OBJ(m_nEdits == m_nLastOrdered, m_enterp, "Cfg was edited but not re-ordered");
return edgep->m_id;
}
// Implementation for insertTwoWayJoins
CfgBlock* getOrCreateTwoWayJoinFor(CfgBlock* bbp);
// CONSTRUCTOR - use CfgGraph::build, which might fail, so this can't be public
CfgGraph() = default;
public:
~CfgGraph() override = default;
// STATIC FUNCTIONS
// Build CFG for the given list of statements
static std::unique_ptr<CfgGraph> build(AstNode* stmtsp);
// PUBLIC METHODS
// Accessors
const BasicBlock& enter() const { return *m_enterp; }
const BasicBlock& exit() const { return *m_exitp; }
const CfgBlock& enter() const { return *m_enterp; }
const CfgBlock& exit() const { return *m_exitp; }
// Number of basic blocks in this graph
size_t nBasicBlocks() const { return m_nBasicBlocks; }
size_t nBlocks() const { return m_nBlocks; }
// Number of control flow edges in this graph
size_t nEdges() const { return m_nEdges; }
// Create a BasicBlock map for this graph
// Create a CfgBlock map for this graph
template <typename T_Value>
BasicBlockMap<T_Value> makeBasicBlockMap() const {
return BasicBlockMap<T_Value>{nBasicBlocks()};
}
// Create a ControlFlowEdgeMap map for this graph
inline CfgBlockMap<T_Value> makeBlockMap() const;
// Create a CfgEdgeMap map for this graph
template <typename T_Value>
ControlFlowEdgeMap<T_Value> makeEdgeMap() const {
return ControlFlowEdgeMap<T_Value>{nEdges()};
}
inline CfgEdgeMap<T_Value> makeEdgeMap() const;
// Returns true iff the graph contains a loop (back-edge)
bool containsLoop() const;
//------------------------------------------------------------------
// The following methods mutate this CFG and invalidate CfgBlock and
// CfgEdge IDs and associated CfgBlockMap, CfgEdgeMap and other
// query instances.
// Remove empty blocks, combine sequential blocks. Keeps the enter/exit block, even if empty.
void minimize();
// Insert empty blocks to fix critical edges (edges that have a source with
// multiple successors, and a destination with multiple predecessors)
void breakCriticalEdges();
bool insertTwoWayJoins();
};
//######################################################################
// Inline method definitions
// CfgMap - Map from CfgBlock or CfgEdge to generic values
BasicBlock::BasicBlock(ControlFlowGraph* cfgp)
: V3GraphVertex{cfgp} {}
template <typename T_Key, typename T_Value>
class CfgMap VL_NOT_FINAL {
// As opposed to a std::map/std::unordered_map, all entries are value
// initialized at construction, and the map is always dense. This can
// be improved if necessary but is sufficient for our current purposes.
const ControlFlowEdge* BasicBlock::takenEdgep() const {
// It's always the first edge
const V3GraphEdge* const frontp = outEdges().frontp();
return static_cast<const ControlFlowEdge*>(frontp);
const CfgGraph* m_cfgp; // The control flow graph this map is for
size_t m_created; // Edit count of CFG this map was created at
std::vector<T_Value> m_map; // The map, stored as a vector
protected:
// CONSTRUCTOR
explicit CfgMap(const CfgGraph* cfgp, size_t size)
: m_cfgp{cfgp}
, m_created{cfgp->m_nEdits}
, m_map{size} {}
public:
// Can create an empty map
CfgMap()
: m_cfgp{nullptr}
, m_created{0} {}
// Copyable, movable
CfgMap(const CfgMap<T_Key, T_Value>&) = default;
CfgMap(CfgMap<T_Key, T_Value>&&) = default;
CfgMap<T_Key, T_Value>& operator=(const CfgMap<T_Key, T_Value>&) = default;
CfgMap<T_Key, T_Value>& operator=(CfgMap<T_Key, T_Value>&&) = default;
T_Value& operator[](const T_Key& key) {
UASSERT_OBJ(m_created == m_cfgp->m_nEdits, m_cfgp->m_enterp, "Map is stale");
UASSERT_OBJ(m_cfgp == key.m_cfgp, m_cfgp->m_enterp, "Key not in this CFG");
return m_map.at(key.id());
}
const ControlFlowEdge* BasicBlock::untknEdgep() const {
// It's always the second (last) edge
const V3GraphEdge* const frontp = outEdges().frontp();
const V3GraphEdge* const backp = outEdges().backp();
return backp != frontp ? static_cast<const ControlFlowEdge*>(backp) : nullptr;
const T_Value& operator[](const T_Key& key) const {
UASSERT_OBJ(m_created == m_cfgp->m_nEdits, m_cfgp->m_enterp, "Map is stale");
UASSERT_OBJ(m_cfgp == key.m_cfgp, m_cfgp->m_enterp, "Key not in this CFG");
return m_map.at(key.id());
}
const BasicBlock* BasicBlock::takenSuccessorp() const {
const ControlFlowEdge* const edgep = takenEdgep();
return edgep ? static_cast<const BasicBlock*>(edgep->top()) : nullptr;
T_Value& operator[](const T_Key* keyp) {
UASSERT_OBJ(m_created == m_cfgp->m_nEdits, m_cfgp->m_enterp, "Map is stale");
UASSERT_OBJ(m_cfgp == keyp->m_cfgp, m_cfgp->m_enterp, "Key not in this CFG");
return m_map.at(keyp->id());
}
const BasicBlock* BasicBlock::untknSuccessorp() const {
const ControlFlowEdge* const edgep = untknEdgep();
return edgep ? static_cast<const BasicBlock*>(edgep->top()) : nullptr;
const T_Value& operator[](const T_Key* keyp) const {
UASSERT_OBJ(m_created == m_cfgp->m_nEdits, m_cfgp->m_enterp, "Map is stale");
UASSERT_OBJ(m_cfgp == keyp->m_cfgp, m_cfgp->m_enterp, "Key not in this CFG");
return m_map.at(keyp->id());
}
};
ControlFlowEdge::ControlFlowEdge(ControlFlowGraph* graphp, BasicBlock* srcp, BasicBlock* dstp)
: V3GraphEdge{graphp, srcp, dstp, 1, false} {}
template <typename T_Value>
class CfgBlockMap final : public CfgMap<CfgBlock, T_Value> {
friend class CfgGraph;
// CONSTRUCTOR - Create one via CfgGraph::makeBlockMap
explicit CfgBlockMap(const CfgGraph* cfgp)
: CfgMap<CfgBlock, T_Value>{cfgp, cfgp->nBlocks()} {}
public:
// Can create an empty map
CfgBlockMap() = default;
// Copyable, movable
CfgBlockMap(const CfgBlockMap&) = default;
CfgBlockMap(CfgBlockMap&&) = default;
CfgBlockMap& operator=(const CfgBlockMap&) = default;
CfgBlockMap& operator=(CfgBlockMap&&) = default;
};
template <typename T_Value>
class CfgEdgeMap final : public CfgMap<CfgEdge, T_Value> {
friend class CfgGraph;
// CONSTRUCTOR - Create one via CfgGraph::makeEdgeMap
explicit CfgEdgeMap(const CfgGraph* cfgp)
: CfgMap<CfgEdge, T_Value>{cfgp, cfgp->nEdges()} {}
public:
// Can create an empty map
CfgEdgeMap() = default;
// Copyable, movable
CfgEdgeMap(const CfgEdgeMap&) = default;
CfgEdgeMap(CfgEdgeMap&&) = default;
CfgEdgeMap& operator=(const CfgEdgeMap&) = default;
CfgEdgeMap& operator=(CfgEdgeMap&&) = default;
};
//######################################################################
// ControlFlowGraph functions
// Innline method definitions
// --- CfgBlock ---
CfgBlock::CfgBlock(CfgGraph* cfgp)
: V3GraphVertex{cfgp}
, m_cfgp{cfgp} {}
size_t CfgBlock::id() { return m_cfgp->idOf(this); }
size_t CfgBlock::id() const { return m_cfgp->idOf(this); }
// Successor edges
CfgEdge* CfgBlock::takenEdgep() { // It's always the first edge
return isExit() ? nullptr : static_cast<CfgEdge*>(outEdges().frontp());
}
const CfgEdge* CfgBlock::takenEdgep() const { // It's always the first edge
return isExit() ? nullptr : static_cast<const CfgEdge*>(outEdges().frontp());
}
CfgEdge* CfgBlock::untknEdgep() { // It's always the second (last) edge
return isBranch() ? static_cast<CfgEdge*>(outEdges().backp()) : nullptr;
}
const CfgEdge* CfgBlock::untknEdgep() const { // It's always the second (last) edge
return isBranch() ? static_cast<const CfgEdge*>(outEdges().backp()) : nullptr;
}
CfgBlock* CfgBlock::takenp() {
return isExit() ? nullptr : static_cast<CfgBlock*>(outEdges().frontp()->top());
}
const CfgBlock* CfgBlock::takenp() const {
return isExit() ? nullptr : static_cast<CfgBlock*>(outEdges().frontp()->top());
}
CfgBlock* CfgBlock::untknp() {
return isBranch() ? static_cast<CfgBlock*>(outEdges().backp()->top()) : nullptr;
}
const CfgBlock* CfgBlock::untknp() const {
return isBranch() ? static_cast<const CfgBlock*>(outEdges().backp()->top()) : nullptr;
}
// Predecessor edges
CfgEdge* CfgBlock::firstPredecessorEdgep() { //
return static_cast<CfgEdge*>(inEdges().frontp());
}
const CfgEdge* CfgBlock::firstPredecessorEdgep() const { //
return static_cast<const CfgEdge*>(inEdges().frontp());
}
CfgEdge* CfgBlock::lastPredecessorEdgep() { //
return static_cast<CfgEdge*>(inEdges().backp());
}
const CfgEdge* CfgBlock::lastPredecessorEdgep() const { //
return static_cast<const CfgEdge*>(inEdges().backp());
}
CfgBlock* CfgBlock::firstPredecessorp() { //
return isEnter() ? nullptr : firstPredecessorEdgep()->srcp();
}
const CfgBlock* CfgBlock::firstPredecessorp() const { //
return isEnter() ? nullptr : firstPredecessorEdgep()->srcp();
}
CfgBlock* CfgBlock::lastPredecessorp() { //
return isEnter() ? nullptr : lastPredecessorEdgep()->srcp();
}
const CfgBlock* CfgBlock::lastPredecessorp() const { //
return isEnter() ? nullptr : lastPredecessorEdgep()->srcp();
}
// --- CfgEdge ---
CfgEdge::CfgEdge(CfgGraph* cfgp, CfgBlock* srcp, CfgBlock* dstp)
: V3GraphEdge{cfgp, srcp, dstp, 1, false}
, m_cfgp{cfgp} {}
size_t CfgEdge::id() { return m_cfgp->idOf(this); }
size_t CfgEdge::id() const { return m_cfgp->idOf(this); }
// --- CfgGraph ---
template <typename T_Value>
CfgBlockMap<T_Value> CfgGraph::makeBlockMap() const {
return CfgBlockMap<T_Value>{this};
}
template <typename T_Value>
CfgEdgeMap<T_Value> CfgGraph::makeEdgeMap() const {
return CfgEdgeMap<T_Value>{this};
}
//######################################################################
// CfgDominatorTree
class CfgDominatorTree final {
// STATE
CfgBlockMap<const CfgBlock*> m_bb2Idom; // Map from CfgBlock to its immediate dominator
// PRIVATE METHODS
// Part of algorithm to compute m_bb2Idom, see consructor
const CfgBlock* intersect(const CfgBlock* ap, const CfgBlock* bp);
public:
// CONSTRUCTOR
explicit CfgDominatorTree(const CfgGraph& cfg);
// Can create an empty map
CfgDominatorTree() = default;
// Copyable, movable
CfgDominatorTree(const CfgDominatorTree&) = default;
CfgDominatorTree(CfgDominatorTree&&) = default;
CfgDominatorTree& operator=(const CfgDominatorTree&) = default;
CfgDominatorTree& operator=(CfgDominatorTree&&) = default;
// PUBLIC METHODS
// Return unique CfgBlock that dominates both of the given blocks, but does
// not strictly dominate any other block that dominates both blocks. It
// will return 'ap' or 'bp' if one dominates the other (or are the same)
const CfgBlock* closestCommonDominator(const CfgBlock* ap, const CfgBlock* bp) const {
while (ap != bp) {
if (*ap < *bp) {
bp = m_bb2Idom[bp];
} else {
ap = m_bb2Idom[ap];
}
}
return ap;
}
// Returns true if 'ap' dominates 'bp'
bool dominates(const CfgBlock* const ap, const CfgBlock* bp) {
// Walk up the dominator tree from 'bp' until reaching 'ap' or the root
while (true) {
// True if 'ap' is above (or same as) 'bp'
if (ap == bp) return true;
// Step up the dominator tree
bp = m_bb2Idom[bp];
// False if reached the root
if (!bp) return false;
}
}
};
//######################################################################
// V3Cfg
namespace V3Cfg {
// Build control flow graph for given node
std::unique_ptr<const ControlFlowGraph> build(const AstNodeProcedure*);
// Compute AstVars live on entry to given CFG. That is, variables that might
// be read before wholly assigned in the CFG. Returns nullptr if the analysis
// failed due to unhandled statements or data types involved in the CFG.
// On success, returns a vector of AstVar or AstVarScope nodes live on entry.
std::unique_ptr<std::vector<AstVar*>> liveVars(const ControlFlowGraph&);
std::unique_ptr<std::vector<AstVar*>> liveVars(const CfgGraph&);
// Same as liveVars, but return AstVarScopes insted
std::unique_ptr<std::vector<AstVarScope*>> liveVarScopes(const ControlFlowGraph&);
std::unique_ptr<std::vector<AstVarScope*>> liveVarScopes(const CfgGraph&);
} //namespace V3Cfg
#endif // VERILATOR_V3CFG_H_

182
src/V3CfgBuilder.cpp
View File

@ -31,35 +31,18 @@
VL_DEFINE_DEBUG_FUNCTIONS;
class CfgBuilder final : VNVisitorConst {
class CfgBuilder final : public VNVisitorConst {
// STATE
// The graph being built, or nullptr if failed to build one
std::unique_ptr<ControlFlowGraph> m_cfgp{new ControlFlowGraph};
std::unique_ptr<CfgGraph> m_cfgp{new CfgGraph};
// Current basic block to add statements to
BasicBlock* m_currBBp = nullptr;
CfgBlock* m_currBBp = nullptr;
// Continuation block for given JumpBlock
std::unordered_map<AstJumpBlock*, BasicBlock*> m_jumpBlockContp;
std::unordered_map<AstJumpBlock*, CfgBlock*> m_jumpBlockContp;
// METHODS
// Create new Basicblock block in the CFG
BasicBlock& addBasicBlock() { return *new BasicBlock{m_cfgp.get()}; }
// Create new taken (or unconditional) ControlFlowEdge in the CFG
void addTakenEdge(BasicBlock& src, BasicBlock& dst) {
UASSERT_OBJ(src.outEmpty(), &src, "Taken edge should be added first");
new ControlFlowEdge{m_cfgp.get(), &src, &dst};
}
// Create new untaken ControlFlowEdge in the CFG
void addUntknEdge(BasicBlock& src, BasicBlock& dst) {
UASSERT_OBJ(src.outSize1(), &src, "Untaken edge shold be added second");
UASSERT_OBJ(src.outEdges().frontp()->top() != &dst, &src,
"Untaken branch targets the same block as the taken branch");
new ControlFlowEdge{m_cfgp.get(), &src, &dst};
}
// Add the given statement to the current BasicBlock
// Add the given statement to the current CfgBlock
void addStmt(AstNodeStmt* nodep) { m_currBBp->m_stmtps.emplace_back(nodep); }
// Used to handle statements not representable in the CFG
@ -115,71 +98,71 @@ class CfgBuilder final : VNVisitorConst {
addStmt(nodep);
// Create then/else/continuation blocks
BasicBlock& thenBB = addBasicBlock();
BasicBlock& elseBB = addBasicBlock();
BasicBlock& contBB = addBasicBlock();
addTakenEdge(*m_currBBp, thenBB);
addUntknEdge(*m_currBBp, elseBB);
CfgBlock* const thenBBp = m_cfgp->addBlock();
CfgBlock* const elseBBp = m_cfgp->addBlock();
CfgBlock* const contBBp = m_cfgp->addBlock();
m_cfgp->addTakenEdge(m_currBBp, thenBBp);
m_cfgp->addUntknEdge(m_currBBp, elseBBp);
// Build then branch
m_currBBp = &thenBB;
m_currBBp = thenBBp;
iterateAndNextConstNull(nodep->thensp());
if (!m_cfgp) return;
if (m_currBBp) addTakenEdge(*m_currBBp, contBB);
if (m_currBBp) m_cfgp->addTakenEdge(m_currBBp, contBBp);
// Build else branch
m_currBBp = &elseBB;
m_currBBp = elseBBp;
iterateAndNextConstNull(nodep->elsesp());
if (!m_cfgp) return;
if (m_currBBp) addTakenEdge(*m_currBBp, contBB);
if (m_currBBp) m_cfgp->addTakenEdge(m_currBBp, contBBp);
// Set continuation
m_currBBp = &contBB;
m_currBBp = contBBp;
}
void visit(AstWhile* nodep) override {
if (!m_cfgp) return;
// Create the header block
BasicBlock& headBB = addBasicBlock();
addTakenEdge(*m_currBBp, headBB);
CfgBlock* const headBBp = m_cfgp->addBlock();
m_cfgp->addTakenEdge(m_currBBp, headBBp);
// The While goes in the header block - semantically the condition check only ...
m_currBBp = &headBB;
m_currBBp = headBBp;
addStmt(nodep);
// Create the body/continuation blocks
BasicBlock& bodyBB = addBasicBlock();
BasicBlock& contBB = addBasicBlock();
addTakenEdge(headBB, bodyBB);
addUntknEdge(headBB, contBB);
CfgBlock* const bodyBBp = m_cfgp->addBlock();
CfgBlock* const contBBp = m_cfgp->addBlock();
m_cfgp->addTakenEdge(headBBp, bodyBBp);
m_cfgp->addUntknEdge(headBBp, contBBp);
// Build the body
m_currBBp = &bodyBB;
m_currBBp = bodyBBp;
iterateAndNextConstNull(nodep->stmtsp());
iterateAndNextConstNull(nodep->incsp());
if (!m_cfgp) return;
if (m_currBBp) addTakenEdge(*m_currBBp, headBB);
if (m_currBBp) m_cfgp->addTakenEdge(m_currBBp, headBBp);
// Set continuation
m_currBBp = &contBB;
m_currBBp = contBBp;
}
void visit(AstJumpBlock* nodep) override {
if (!m_cfgp) return;
// Don't acutally need to add this 'nodep' to any block - but we could later if needed
// Don't acutally need to add this 'nodep' to any block
// Create continuation block
BasicBlock& contBB = addBasicBlock();
const bool newEntry = m_jumpBlockContp.emplace(nodep, &contBB).second;
CfgBlock* const contBBp = m_cfgp->addBlock();
const bool newEntry = m_jumpBlockContp.emplace(nodep, contBBp).second;
UASSERT_OBJ(newEntry, nodep, "AstJumpBlock visited twice");
// Build the body
iterateAndNextConstNull(nodep->stmtsp());
if (!m_cfgp) return;
if (m_currBBp) addTakenEdge(*m_currBBp, contBB);
if (m_currBBp) m_cfgp->addTakenEdge(m_currBBp, contBBp);
// Set continuation
m_currBBp = &contBB;
m_currBBp = contBBp;
}
void visit(AstJumpGo* nodep) override {
if (!m_cfgp) return;
@ -190,102 +173,61 @@ class CfgBuilder final : VNVisitorConst {
return;
}
// Don't acutally need to add this 'nodep' to any block - but we could later if needed
// Don't acutally need to add this 'nodep' to any block
// Make current block go to the continuation of the JumpBlock
addTakenEdge(*m_currBBp, *m_jumpBlockContp.at(nodep->blockp()));
m_cfgp->addTakenEdge(m_currBBp, m_jumpBlockContp.at(nodep->blockp()));
// There should be no statements after a JumpGo!
m_currBBp = nullptr;
}
// CONSTRUCTOR
explicit CfgBuilder(const AstNodeProcedure* nodep) {
explicit CfgBuilder(AstNode* stmtsp) {
// Build the graph, starting from the entry block
m_currBBp = &addBasicBlock();
m_currBBp = m_cfgp->addBlock();
m_cfgp->m_enterp = m_currBBp;
// Visit each statement to build the control flow graph
iterateAndNextConstNull(nodep->stmtsp());
iterateAndNextConstNull(stmtsp);
// If failed, stop now
if (!m_cfgp) return;
// The final block is the exit block
m_cfgp->m_exitp = m_currBBp;
// Remove empty blocks - except enter/exit
// Some blocks might not have predecessors if they are unreachable, remove them
{
std::vector<V3GraphVertex*> unreachableps;
for (V3GraphVertex* const vtxp : m_cfgp->vertices().unlinkable()) {
if (vtxp == &m_cfgp->enter()) continue;
if (vtxp == &m_cfgp->exit()) continue;
BasicBlock* const bbp = vtxp->as<BasicBlock>();
if (!bbp->stmtps().empty()) continue;
UASSERT(bbp->outSize1(), "Empty block should have a single successor");
BasicBlock* const succp = const_cast<BasicBlock*>(bbp->takenSuccessorp());
for (V3GraphEdge* const edgep : bbp->inEdges().unlinkable()) edgep->relinkTop(succp);
vtxp->unlinkDelete(m_cfgp.get());
if (vtxp == m_cfgp->m_enterp) continue;
if (vtxp == m_cfgp->m_exitp) continue;
UASSERT_OBJ(!vtxp->outEmpty(), vtxp, "Block with no successor other than exit");
if (vtxp->inEmpty()) unreachableps.emplace_back(vtxp);
}
// Remove redundant entry block
while (m_cfgp->enter().stmtps().empty() && m_cfgp->enter().outSize1()) {
BasicBlock* const succp = m_cfgp->enter().outEdges().frontp()->top()->as<BasicBlock>();
if (!succp->inSize1()) break;
m_cfgp->m_enterp->unlinkDelete(m_cfgp.get());
m_cfgp->m_enterp = succp;
while (!unreachableps.empty()) {
V3GraphVertex* const vtxp = unreachableps.back();
unreachableps.pop_back();
for (V3GraphEdge& edge : vtxp->outEdges()) {
--m_cfgp->m_nEdges;
if (edge.top()->inSize1()) unreachableps.emplace_back(edge.top());
}
// Remove redundant exit block
while (m_cfgp->exit().stmtps().empty() && m_cfgp->exit().inSize1()) {
BasicBlock* const prep = m_cfgp->exit().inEdges().frontp()->fromp()->as<BasicBlock>();
if (!prep->outSize1()) break;
m_cfgp->m_exitp->unlinkDelete(m_cfgp.get());
m_cfgp->m_exitp = prep;
}
// Compute reverse post-order enumeration and sort blocks, assign IDs
{
// Simple recursive algorith will do ...
std::vector<BasicBlock*> postOrderEnumeration;
std::unordered_set<BasicBlock*> visited;
const std::function<void(BasicBlock*)> visitBasicBlock = [&](BasicBlock* bbp) {
// Mark and skip if already visited
if (!visited.emplace(bbp).second) return;
// Visit successors
for (const V3GraphEdge& e : bbp->outEdges()) {
visitBasicBlock(static_cast<BasicBlock*>(e.top()));
}
// Add to post order enumeration
postOrderEnumeration.emplace_back(bbp);
};
visitBasicBlock(m_cfgp->m_enterp);
const uint32_t n = postOrderEnumeration.size();
UASSERT_OBJ(n == m_cfgp->vertices().size(), nodep, "Inconsistent enumeration size");
// Set size in graph
m_cfgp->m_nBasicBlocks = n;
// Assign ids equal to the reverse post order number and sort vertices
for (uint32_t i = 0; i < postOrderEnumeration.size(); ++i) {
BasicBlock* const bbp = postOrderEnumeration[n - 1 - i];
bbp->user(i);
m_cfgp->vertices().unlink(bbp);
m_cfgp->vertices().linkBack(bbp);
--m_cfgp->m_nBlocks;
VL_DO_DANGLING(vtxp->unlinkDelete(m_cfgp.get()), vtxp);
}
}
// Assign IDs to edges
{
size_t nEdges = 0;
for (V3GraphVertex& v : m_cfgp->vertices()) {
for (V3GraphEdge& e : v.outEdges()) e.user(nEdges++);
// Dump the initial graph
if (dumpGraphLevel() >= 9) {
m_cfgp->rpoBlocks();
m_cfgp->dumpDotFilePrefixed("cfg-builder-initial");
}
// Set size in graph
m_cfgp->m_nEdges = nEdges;
}
if (dumpGraphLevel() >= 9) m_cfgp->dumpDotFilePrefixed("cfgbuilder");
// Minimize it
m_cfgp->minimize();
// Dump the final graph
if (dumpGraphLevel() >= 8) m_cfgp->dumpDotFilePrefixed("cfg-builder");
}
public:
static std::unique_ptr<ControlFlowGraph> apply(const AstNodeProcedure* nodep) {
return std::move(CfgBuilder{nodep}.m_cfgp);
static std::unique_ptr<CfgGraph> apply(AstNode* stmtsp) {
return std::move(CfgBuilder{stmtsp}.m_cfgp);
}
};
std::unique_ptr<const ControlFlowGraph> V3Cfg::build(const AstNodeProcedure* nodep) {
return CfgBuilder::apply(nodep);
}
std::unique_ptr<CfgGraph> CfgGraph::build(AstNode* stmtsp) { return CfgBuilder::apply(stmtsp); }

27
src/V3CfgLiveVariables.cpp
View File

@ -49,9 +49,9 @@ class CfgLiveVariables final : VNVisitorConst {
};
// STATE
const ControlFlowGraph& m_cfg; // The CFG beign analysed
const CfgGraph& m_cfg; // The CFG beign analysed
// State for each block
BasicBlockMap<BlockState> m_blockState = m_cfg.makeBasicBlockMap<BlockState>();
CfgBlockMap<BlockState> m_blockState{m_cfg.makeBlockMap<BlockState>()};
BlockState* m_currp = nullptr; // State of current block being analysed
bool m_abort = false; // Abort analysis - unhandled construct
@ -140,7 +140,7 @@ class CfgLiveVariables final : VNVisitorConst {
}
// Apply transfer function of block, return true if changed
bool transfer(const BasicBlock& bb) {
bool transfer(const CfgBlock& bb) {
BlockState& state = m_blockState[bb];
// liveIn = gen union (liveOut - kill)
@ -172,20 +172,21 @@ class CfgLiveVariables final : VNVisitorConst {
void visit(AstWhile* nodep) override { single(nodep->condp()); }
// CONSTRUCTOR
explicit CfgLiveVariables(const ControlFlowGraph& cfg)
explicit CfgLiveVariables(const CfgGraph& cfg)
: m_cfg{cfg} {
// For each basic block, compute the gen and kill set via visit
cfg.foreach([&](const BasicBlock& bb) {
for (const V3GraphVertex& vtx : cfg.vertices()) {
const CfgBlock& bb = static_cast<const CfgBlock&>(vtx);
if (m_abort) return;
VL_RESTORER(m_currp);
m_currp = &m_blockState[bb];
for (AstNode* const stmtp : bb.stmtps()) iterateConst(stmtp);
});
}
if (m_abort) return;
// Perform the flow analysis
std::deque<const BasicBlock*> workList;
const auto enqueue = [&](const BasicBlock& bb) {
std::deque<const CfgBlock*> workList;
const auto enqueue = [&](const CfgBlock& bb) {
BlockState& state = m_blockState[bb];
if (state.m_isOnWorkList) return;
state.m_isOnWorkList = true;
@ -195,13 +196,13 @@ class CfgLiveVariables final : VNVisitorConst {
enqueue(cfg.exit());
while (!workList.empty()) {
const BasicBlock* const currp = workList.front();
const CfgBlock* const currp = workList.front();
workList.pop_front();
BlockState& state = m_blockState[*currp];
state.m_isOnWorkList = false;
// Compute meet (liveOut = union liveIn of successors)
currp->forEachSuccessor([&](const BasicBlock& bb) {
currp->forEachSuccessor([&](const CfgBlock& bb) {
auto& liveIn = m_blockState[bb].m_liveIn;
state.m_liveOut.insert(liveIn.begin(), liveIn.end());
});
@ -216,7 +217,7 @@ class CfgLiveVariables final : VNVisitorConst {
}
public:
static std::unique_ptr<std::vector<Variable*>> apply(const ControlFlowGraph& cfg) {
static std::unique_ptr<std::vector<Variable*>> apply(const CfgGraph& cfg) {
CfgLiveVariables analysis{cfg};
// If failed, return nullptr
if (analysis.m_abort) return nullptr;
@ -231,10 +232,10 @@ public:
}
};
std::unique_ptr<std::vector<AstVar*>> V3Cfg::liveVars(const ControlFlowGraph& cfg) {
std::unique_ptr<std::vector<AstVar*>> V3Cfg::liveVars(const CfgGraph& cfg) {
return CfgLiveVariables</* T_Scoped: */ false>::apply(cfg);
}
std::unique_ptr<std::vector<AstVarScope*>> V3Cfg::liveVarScopes(const ControlFlowGraph& cfg) {
std::unique_ptr<std::vector<AstVarScope*>> V3Cfg::liveVarScopes(const CfgGraph& cfg) {
return CfgLiveVariables</* T_Scoped: */ true>::apply(cfg);
}

6
src/V3DfgAstToDfg.cpp
View File

@ -57,7 +57,7 @@ class AstToDfgVisitor final : public VNVisitor {
}
}
std::unique_ptr<std::vector<Variable*>> getLiveVariables(const ControlFlowGraph& cfg) {
std::unique_ptr<std::vector<Variable*>> getLiveVariables(const CfgGraph& cfg) {
// TODO: remove the useless reinterpret_casts when C++17 'if constexpr' actually works
if VL_CONSTEXPR_CXX17 (T_Scoped) {
std::unique_ptr<std::vector<AstVarScope*>> result = V3Cfg::liveVarScopes(cfg);
@ -139,7 +139,7 @@ class AstToDfgVisitor final : public VNVisitor {
// Gather variables live in to the given CFG.
// Return nullptr if any are not supported.
std::unique_ptr<std::vector<DfgVertexVar*>> gatherLive(const ControlFlowGraph& cfg) {
std::unique_ptr<std::vector<DfgVertexVar*>> gatherLive(const CfgGraph& cfg) {
// Run analysis
std::unique_ptr<std::vector<Variable*>> varps = getLiveVariables(cfg);
if (!varps) {
@ -206,7 +206,7 @@ class AstToDfgVisitor final : public VNVisitor {
// Potentially convertible block
++m_ctx.m_inputs;
// Attempt to build CFG of AstAlways, give up if failed
std::unique_ptr<const ControlFlowGraph> cfgp = V3Cfg::build(nodep);
std::unique_ptr<CfgGraph> cfgp = CfgGraph::build(nodep->stmtsp());
if (!cfgp) {
++m_ctx.m_nonRepCfg;
return false;

16
src/V3DfgContext.h
View File

@ -251,7 +251,13 @@ public:
// Reverted
VDouble0 revertNonSyn; // Reverted due to being driven from non-synthesizable vertex
VDouble0 revertMultidrive; // Reverted due to multiple drivers
// Additional stats
VDouble0 cfgTrivial; // Trivial input CFGs
VDouble0 cfgSp; // Series-paralel input CFGs
VDouble0 cfgDag; // Generic loop free input CFGs
VDouble0 cfgCyclic; // Cyclic input CFGs
VDouble0 joinUsingPathPredicate; // Num control flow joins using full path predicate
VDouble0 joinUsingBranchCondition; // Num Control flow joins using dominating branch cond
} m_synt;
private:
@ -314,6 +320,14 @@ private:
nSyntExpect -= m_synt.synthAlways;
nSyntExpect -= m_synt.synthAssign;
UASSERT(nSyntNonSyn == nSyntExpect, "Inconsistent statistics / synt");
addStat("synt / input CFG trivial", m_synt.cfgTrivial);
addStat("synt / input CFG sp", m_synt.cfgSp);
addStat("synt / input CFG dag", m_synt.cfgDag);
addStat("synt / input CFG cyclic", m_synt.cfgCyclic);
addStat("synt / joins using path predicate", m_synt.joinUsingPathPredicate);
addStat("synt / joins using branch condition", m_synt.joinUsingBranchCondition);
}
};

301
src/V3DfgSynthesize.cpp
View File

@ -508,15 +508,23 @@ class AstToDfgSynthesize final {
bool operator<=(const Driver& other) const { return !(other < *this); }
};
// STATE
// STATE - Persistent
DfgGraph& m_dfg; // The graph being built
V3DfgSynthesisContext& m_ctx; // The context for stats
AstToDfgConverter<T_Scoped> m_converter; // The convert instance to use for each construct
DfgLogic* m_logicp = nullptr; // Current logic vertex we are synthesizing
// Some debug aid: We stop after synthesizing s_dfgSynthDebugLimit vertices (if non-zero).
// This is the problematic logic (last one we synthesize), assuming a bisection search
// over s_dfgSynthDebugLimit.
// STATE - for current DfgLogic being synthesized
DfgLogic* m_logicp = nullptr; // Current logic vertex we are synthesizing
CfgBlockMap<SymTab> m_bbToISymTab; // Map from CfgBlock -> input symbol table
CfgBlockMap<SymTab> m_bbToOSymTab; // Map from CfgBlock -> output symbol table
CfgBlockMap<DfgVertex*> m_bbToCondp; // Map from CfgBlock -> terminating branch condition
CfgEdgeMap<DfgVertex*> m_edgeToPredicatep; // Map CfgGraphEdge -> path predicate to get there
CfgDominatorTree m_domTree; // The dominator tree of the current CFG
// STATE - Some debug aid
// We stop after synthesizing s_dfgSynthDebugLimit vertices (if non-zero).
// This is the problematic logic (last one we synthesize), assuming a
// bisection search over s_dfgSynthDebugLimit.
DfgLogic* m_debugLogicp = nullptr;
// Source (upstream) cone of outputs of m_debugLogicp
std::unique_ptr<std::unordered_set<const DfgVertex*>> m_debugOSrcConep{nullptr};
@ -869,7 +877,7 @@ class AstToDfgSynthesize final {
});
}
// Initialzie input symbol table of entry BasicBlock
// Initialzie input symbol table of entry CfgBlock
void initializeEntrySymbolTable(SymTab& iSymTab) {
m_logicp->forEachSource([&](DfgVertex& src) {
DfgVertexVar* const vvp = src.as<DfgVertexVar>();
@ -991,75 +999,152 @@ class AstToDfgSynthesize final {
return joinp;
}
// Combine the output symbol tables of the predecessors of the given
// BasicBlock to compute the input symtol table for the given block.
bool createInputSymbolTable(SymTab& joined, const BasicBlock& bb,
const BasicBlockMap<SymTab>& bbToOSymTab,
const ControlFlowEdgeMap<DfgVertex*>& edgeToPredicatep) {
// Input symbol table of entry block was previously initialzied
if (bb.inEmpty()) return true;
// We will fill it in here
UASSERT(joined.empty(), "Unresolved input symbol table should be empty");
// Fast path if there is only one predecessor
if (bb.inSize1()) {
joined = bbToOSymTab[*(bb.inEdges().frontp()->fromp()->as<BasicBlock>())];
return true;
}
// Gather predecessors and the path predicates
struct Predecessor final {
const BasicBlock* m_bbp;
DfgVertex* m_predicatep;
Predecessor() = delete;
Predecessor(const BasicBlock* bbp, DfgVertex* predicatep)
: m_bbp{bbp}
, m_predicatep{predicatep} {}
};
const std::vector<Predecessor> predecessors = [&]() {
std::vector<Predecessor> res;
for (const V3GraphEdge& edge : bb.inEdges()) {
const ControlFlowEdge& cfgEdge = static_cast<const ControlFlowEdge&>(edge);
res.emplace_back(&cfgEdge.src(), edgeToPredicatep[cfgEdge]);
}
// Sort predecessors topologically. This way later blocks will come
// after earlier blocks, and the entry block will be first if present.
std::sort(res.begin(), res.end(), [](const Predecessor& a, const Predecessor& b) { //
return a.m_bbp->id() < b.m_bbp->id();
});
return res;
}();
// Start by copying the bindings from the oldest predecessor
joined = bbToOSymTab[*predecessors[0].m_bbp];
// Join over all other predecessors
for (size_t i = 1; i < predecessors.size(); ++i) {
DfgVertex* const predicatep = predecessors[i].m_predicatep;
const SymTab& oSymTab = bbToOSymTab[*predecessors[i].m_bbp];
// Merge 'thenSymTab' into 'elseSymTab' using the given predicate to join values
bool joinSymbolTables(SymTab& elseSymTab, DfgVertex* predicatep, const SymTab& thenSymTab) {
// Give up if something is not assigned on all paths ... Latch?
if (joined.size() != oSymTab.size()) {
if (thenSymTab.size() != elseSymTab.size()) {
++m_ctx.m_synt.nonSynLatch;
return false;
}
// Join each symbol
for (auto& pair : joined) {
for (std::pair<Variable* const, DfgVertexVar*>& pair : elseSymTab) {
Variable* const varp = pair.first;
// Find same variable on other path
auto it = oSymTab.find(varp);
// Find same variable on the else path
auto it = thenSymTab.find(varp);
// Give up if something is not assigned on all paths ... Latch?
if (it == oSymTab.end()) {
if (it == thenSymTab.end()) {
++m_ctx.m_synt.nonSynLatch;
return false;
}
// Join paths with the block predicate
// Join paths with the predicate
DfgVertexVar* const thenp = it->second;
DfgVertexVar* const elsep = pair.second;
DfgVertexVar* const newp = joinDrivers(varp, predicatep, thenp, elsep);
if (!newp) return false;
pair.second = newp;
}
// Done
return true;
}
// Given two joining control flow edges, compute how to join their symbols.
// Returns the predicaete to join over, and the 'then' and 'else' blocks.
std::tuple<DfgVertex*, const CfgBlock*, const CfgBlock*> //
howToJoin(const CfgEdge* const ap, const CfgEdge* const bp) {
// Find the closest common dominator of the two paths
const CfgBlock* const domp = m_domTree.closestCommonDominator(ap->srcp(), bp->srcp());
// These paths join here, so 'domp' must be a branch, otherwise it's not the closest
UASSERT_OBJ(domp->isBranch(), domp, "closestCommonDominator is not a branch");
// The branches of the common dominator
const CfgEdge* const takenEdgep = domp->takenEdgep();
const CfgEdge* const untknEdgep = domp->untknEdgep();
// We check if the taken branch dominates the path to either blocks,
// and if the untaken branch dominates the path to the other block.
// If so, we can use the branch condition as predicate, otherwise
// we must use the path predicate as there are ways to get from one
// branch of the dominator to the other. We need to be careful if
// either branches are directly to the join block. This is fine,
// it's as if there was an empty block on that critical edge which
// is dominated by that path.
if (takenEdgep == ap || m_domTree.dominates(takenEdgep->dstp(), ap->srcp())) {
if (untknEdgep == bp || m_domTree.dominates(untknEdgep->dstp(), bp->srcp())) {
// Taken path dominates 'ap' and untaken dominates 'bp', use the branch condition
++m_ctx.m_synt.joinUsingBranchCondition;
return std::make_tuple(m_bbToCondp[domp], ap->srcp(), bp->srcp());
}
} else if (takenEdgep == bp || m_domTree.dominates(takenEdgep->dstp(), bp->srcp())) {
if (untknEdgep == ap || m_domTree.dominates(untknEdgep->dstp(), ap->srcp())) {
// Taken path dominates 'bp' and untaken dominates 'ap', use the branch condition
++m_ctx.m_synt.joinUsingBranchCondition;
return std::make_tuple(m_bbToCondp[domp], bp->srcp(), ap->srcp());
}
}
// The branches don't dominate the joined blocks, must use the path predicate
++m_ctx.m_synt.joinUsingPathPredicate;
// TODO: We could do better here: use the path predicate of the closest
// cominating blocks, pick the one from the lower rank, etc, but this
// generic case is very rare, most synthesizable logic has
// series-parallel CFGs which are covered by the earlier cases.
return std::make_tuple(m_edgeToPredicatep[ap], ap->srcp(), bp->srcp());
}
// Combine the output symbol tables of the predecessors of the given
// block to compute the input symtol table for the given block.
bool createInputSymbolTable(const CfgBlock& bb) {
// The input symbol table of the given block, we are computing it now
SymTab& joined = m_bbToISymTab[bb];
// Input symbol table of entry block is special
if (bb.isEnter()) {
initializeEntrySymbolTable(joined);
return true;
}
// Current input symbol table should be empty, we will fill it in here
UASSERT(joined.empty(), "Unprocessed input symbol table should be empty");
// Fast path if there is only one predecessor - TODO: use less copying
if (!bb.isJoin()) {
joined = m_bbToOSymTab[bb.firstPredecessorp()];
return true;
}
// We also have a simpler job if there are 2 predecessors
if (bb.isTwoWayJoin()) {
DfgVertex* predicatep = nullptr;
const CfgBlock* thenp = nullptr;
const CfgBlock* elsep = nullptr;
std::tie(predicatep, thenp, elsep)
= howToJoin(bb.firstPredecessorEdgep(), bb.lastPredecessorEdgep());
// Copy from else
joined = m_bbToOSymTab[elsep];
// Join with then
return joinSymbolTables(joined, predicatep, m_bbToOSymTab[*thenp]);
}
// General hard way
// Gather predecessors
struct Predecessor final {
const CfgBlock* m_bbp; // Predeccessor block
DfgVertex* m_predicatep; // Predicate predecessor reached this block with
const SymTab* m_oSymTabp; // Output symbol table or predecessor
Predecessor() = delete;
Predecessor(const CfgBlock* bbp, DfgVertex* predicatep, const SymTab* oSymTabp)
: m_bbp{bbp}
, m_predicatep{predicatep}
, m_oSymTabp{oSymTabp} {}
};
const std::vector<Predecessor> predecessors = [&]() {
std::vector<Predecessor> res;
for (const V3GraphEdge& edge : bb.inEdges()) {
const CfgEdge& cfgEdge = static_cast<const CfgEdge&>(edge);
const CfgBlock* const predecessorp = cfgEdge.srcp();
DfgVertex* const predicatep = m_edgeToPredicatep[cfgEdge];
const SymTab* const oSymTabp = &m_bbToOSymTab[predecessorp];
res.emplace_back(predecessorp, predicatep, oSymTabp);
}
// Sort predecessors reverse topologically. This way earlier blocks
// will come after later blocks, and the entry block is last if present.
std::sort(res.begin(), res.end(), [](const Predecessor& a, const Predecessor& b) { //
return *a.m_bbp > *b.m_bbp;
});
return res;
}();
// Start by copying the bindings from the frist predecessor
joined = *predecessors[0].m_oSymTabp;
// Join over all other predecessors
for (size_t i = 1; i < predecessors.size(); ++i) {
DfgVertex* const predicatep = predecessors[i].m_predicatep;
const SymTab& oSymTab = *predecessors[i].m_oSymTabp;
if (!joinSymbolTables(joined, predicatep, oSymTab)) return false;
}
return true;
@ -1169,7 +1254,7 @@ class AstToDfgSynthesize final {
}
// Synthesize the given statements with the given input symbol table.
// Returnt true if successfolly synthesized.
// Returns true if successfolly synthesized.
// Populates the given output symbol table.
// Populates the given reference with the condition of the terminator branch, if any.
bool synthesizeBasicBlock(SymTab& oSymTab, DfgVertex*& condpr,
@ -1259,39 +1344,37 @@ class AstToDfgSynthesize final {
return true;
}
// Given a basic block, and the condition of the terminating branch (if any),
// assign perdicates to the block's outgoing control flow edges.
void assignSuccessorPredicates(ControlFlowEdgeMap<DfgVertex*>& edgeToPredicatep,
const BasicBlock& bb, DfgVertex* condp) {
// Assign path perdicates to the outgoing control flow edges of the given block
void assignPathPredicates(const CfgBlock& bb) {
// Nothing to do for the exit block
if (bb.outEmpty()) return;
if (bb.isExit()) return;
// Get the predicate of this block
DfgVertex* const predp = [&]() -> DfgVertex* {
// Entry block has no predecessors, use constant true
if (bb.inEmpty()) return make<DfgConst>(m_logicp->fileline(), 1U, 1U);
if (bb.isEnter()) return make<DfgConst>(m_logicp->fileline(), 1U, 1U);
// For any other block, 'or' together all the incoming predicates
const auto& inEdges = bb.inEdges();
auto it = inEdges.begin();
DfgVertex* resp = edgeToPredicatep[static_cast<const ControlFlowEdge&>(*it)];
DfgVertex* resp = m_edgeToPredicatep[static_cast<const CfgEdge&>(*it)];
while (++it != inEdges.end()) {
DfgOr* const orp = make<DfgOr>(resp->fileline(), resp->dtypep());
orp->rhsp(resp);
orp->lhsp(edgeToPredicatep[static_cast<const ControlFlowEdge&>(*it)]);
orp->lhsp(m_edgeToPredicatep[static_cast<const CfgEdge&>(*it)]);
resp = orp;
}
return resp;
}();
if (!condp) {
// There should be 1 successors for a block with an unconditional terminator
UASSERT_OBJ(!bb.untknEdgep(), predp, "Expecting 1 successor for BasicBlock");
// Successor predicate edge is the same
edgeToPredicatep[*bb.takenEdgep()] = predp;
} else {
// There should be 2 successors for a block with an conditional terminator
UASSERT_OBJ(bb.untknEdgep(), predp, "Expecting 2 successors for BasicBlock");
// For uncondional branches, the successor predicate edge is the same
if (!bb.isBranch()) {
m_edgeToPredicatep[bb.takenEdgep()] = predp;
return;
}
// For branches, we need to factor in the branch condition
DfgVertex* const condp = m_bbToCondp[bb];
FileLine* const flp = condp->fileline();
AstNodeDType* const dtypep = condp->dtypep(); // Single bit
@ -1299,7 +1382,7 @@ class AstToDfgSynthesize final {
DfgAnd* const takenPredp = make<DfgAnd>(flp, dtypep);
takenPredp->lhsp(predp);
takenPredp->rhsp(condp);
edgeToPredicatep[*bb.takenEdgep()] = takenPredp;
m_edgeToPredicatep[bb.takenEdgep()] = takenPredp;
// Predicate for untaken branch: 'predp & ~condp'
DfgAnd* const untknPredp = make<DfgAnd>(flp, dtypep);
@ -1307,8 +1390,7 @@ class AstToDfgSynthesize final {
DfgNot* const notp = make<DfgNot>(flp, dtypep);
notp->srcp(condp);
untknPredp->rhsp(notp);
edgeToPredicatep[*bb.untknEdgep()] = untknPredp;
}
m_edgeToPredicatep[bb.untknEdgep()] = untknPredp;
}
// Add the synthesized values as drivers to the output variables of the current DfgLogic
@ -1359,7 +1441,7 @@ class AstToDfgSynthesize final {
// Initialzie input symbol table
initializeEntrySymbolTable(iSymTab);
// Synthesize as if it was in a single BasicBlock CFG
// Synthesize as if it was in a single CfgBlock CFG
DfgVertex* condp = nullptr;
const bool success = synthesizeBasicBlock(oSymTab, condp, {assignp}, iSymTab);
UASSERT_OBJ(!condp, nodep, "Conditional AstAssignW ???");
@ -1372,7 +1454,7 @@ class AstToDfgSynthesize final {
}
// Synthesize the given AstAlways. Returns true on success.
bool synthesizeCfg(const ControlFlowGraph& cfg) {
bool synthesizeCfg(CfgGraph& cfg) {
++m_ctx.m_synt.inputAlways;
if (hasExternallyWrittenVariable(*m_logicp)) {
@ -1383,37 +1465,48 @@ class AstToDfgSynthesize final {
// If there is a backward edge (loop), we can't synthesize it
if (cfg.containsLoop()) {
++m_ctx.m_synt.nonSynLoop;
++m_ctx.m_synt.cfgCyclic;
return false;
}
// Maps from BasicBlock to its input and output symbol tables
BasicBlockMap<SymTab> bbToISymTab = cfg.makeBasicBlockMap<SymTab>();
BasicBlockMap<SymTab> bbToOSymTab = cfg.makeBasicBlockMap<SymTab>();
// If it's a trivial CFG we can save on some work
if (cfg.nBlocks() == 1) {
++m_ctx.m_synt.cfgTrivial;
} else {
// Insert two-way join blocks to aid multiplexer ordering
if (cfg.insertTwoWayJoins()) {
++m_ctx.m_synt.cfgSp;
} else {
++m_ctx.m_synt.cfgDag;
}
// Initialize maps needed for non-trivial CFGs
m_domTree = CfgDominatorTree{cfg};
m_edgeToPredicatep = cfg.makeEdgeMap<DfgVertex*>();
}
// Map from ControlFlowGraphEdge to its predicate
ControlFlowEdgeMap<DfgVertex*> edgeToPredicatep = cfg.makeEdgeMap<DfgVertex*>();
// Initialzie input symbol table of entry block
initializeEntrySymbolTable(bbToISymTab[cfg.enter()]);
// Initialize CfgMaps
m_bbToISymTab = cfg.makeBlockMap<SymTab>();
m_bbToOSymTab = cfg.makeBlockMap<SymTab>();
m_bbToCondp = cfg.makeBlockMap<DfgVertex*>();
// Synthesize all blocks
for (const V3GraphVertex& cfgVtx : cfg.vertices()) {
const BasicBlock& bb = *cfgVtx.as<BasicBlock>();
// Symbol tables of the block
SymTab& iSymTab = bbToISymTab[bb];
SymTab& oSymTab = bbToOSymTab[bb];
// Join symbol tables from predecessor blocks
if (!createInputSymbolTable(iSymTab, bb, bbToOSymTab, edgeToPredicatep)) return false;
// Condition of the terminating branch, if any
DfgVertex* condp = nullptr;
// Synthesize the block
if (!synthesizeBasicBlock(oSymTab, condp, bb.stmtps(), iSymTab)) return false;
// Set the predicates on the successor edges
assignSuccessorPredicates(edgeToPredicatep, bb, condp);
for (const V3GraphVertex& vtx : cfg.vertices()) {
const CfgBlock& bb = static_cast<const CfgBlock&>(vtx);
// Prepare the input symbol table of this block (enter, or join predecessor blocks)
if (!createInputSymbolTable(bb)) return false;
// Synthesize this block
if (!synthesizeBasicBlock(m_bbToOSymTab[bb], //
m_bbToCondp[bb], //
bb.stmtps(), //
m_bbToISymTab[bb])) {
return false;
}
// Set the path predicates on the successor edges
assignPathPredicates(bb);
}
// Add resolved output variable drivers
return addSynthesizedOutput(bbToOSymTab[cfg.exit()]);
return addSynthesizedOutput(m_bbToOSymTab[cfg.exit()]);
}
// Synthesize a DfgLogic into regular vertices. Returns ture on success.
@ -1676,7 +1769,7 @@ void V3DfgPasses::synthesize(DfgGraph& dfg, V3DfgContext& ctx) {
if (VN_IS(logicp->nodep(), AssignW)) return true;
// Synthesize always blocks with no more than 4 basic blocks and 4 edges
// These are usually simple branches (if (rst) ... else ...), or close to it
return logicp->cfg().nBasicBlocks() <= 4 && logicp->cfg().nEdges() <= 4;
return logicp->cfg().nBlocks() <= 4 && logicp->cfg().nEdges() <= 4;
});
if (doIt) varps.emplace_back(&var);
}

7
src/V3DfgVertices.h
View File

@ -346,7 +346,7 @@ public:
class DfgLogic final : public DfgVertexVariadic {
// Generic vertex representing a whole combinational process
AstNode* const m_nodep; // The Ast logic represented by this vertex
const std::unique_ptr<const ControlFlowGraph> m_cfgp;
const std::unique_ptr<CfgGraph> m_cfgp;
// Vertices this logic was synthesized into. Excluding variables
std::vector<DfgVertex*> m_synth;
@ -356,7 +356,7 @@ public:
, m_nodep{nodep}
, m_cfgp{nullptr} {}
DfgLogic(DfgGraph& dfg, AstAlways* nodep, std::unique_ptr<const ControlFlowGraph> cfgp)
DfgLogic(DfgGraph& dfg, AstAlways* nodep, std::unique_ptr<CfgGraph> cfgp)
: DfgVertexVariadic{dfg, dfgType(), nodep->fileline(), nullptr, 1u}
, m_nodep{nodep}
, m_cfgp{std::move(cfgp)} {}
@ -366,7 +366,8 @@ public:
void addInput(DfgVertexVar* varp) { addSource()->relinkSource(varp); }
AstNode* nodep() const { return m_nodep; }
const ControlFlowGraph& cfg() const { return *m_cfgp; }
CfgGraph& cfg() { return *m_cfgp; }
const CfgGraph& cfg() const { return *m_cfgp; }
std::vector<DfgVertex*>& synth() { return m_synth; }
const std::vector<DfgVertex*>& synth() const { return m_synth; }

1
src/V3List.h
View File

@ -241,6 +241,7 @@ public:
bool empty() const { return !m_headp; }
bool hasSingleElement() const { return m_headp && m_headp == m_lastp; }
bool hasMultipleElements() const { return m_headp && m_headp != m_lastp; }
bool hasTwoElements() const { return m_headp && toLinks(m_headp).m_nextp == m_lastp; }
// These return pointers, as we often want to unlink/delete them, and can also signal empty
T_Element* frontp() { return static_cast<T_Element*>(m_headp); }

5
test_regress/t/t_dfg_break_cycles.py
View File

@ -44,9 +44,10 @@ with open(rdFile, 'r', encoding="utf8") as rdFh, \
open(pdeclFile, 'w', encoding="utf8") as pdeclFh, \
open(checkFile, 'w', encoding="utf8") as checkFh:
for line in rdFh:
if "// UNOPTFLAT" in line:
line, _, cmt = line.partition("//")
cmt, _, _ = cmt.partition("//")
if "UNOPTFLAT" in cmt:
nExpectedCycles += 1
line = line.split("//")[0]
m = re.search(r'`signal\((\w+),', line)
if not m:
continue

10
test_regress/t/t_dfg_synthesis.py
View File

@ -70,13 +70,14 @@ test.compile(verilator_flags2=[
"--stats",
"--build",
"--fdfg-synthesize-all",
"-fno-dfg-pre-inline",
"-fno-dfg-post-inline",
"-fno-dfg-scoped",
"--exe",
"+incdir+" + test.obj_dir,
"-Mdir", test.obj_dir + "/obj_opt",
"--prefix", "Vopt",
"-fno-const-before-dfg", # Otherwise V3Const makes testing painful
"-fno-split", # Dfg will take care of it
"--debug", "--debugi", "0", "--dumpi-tree", "0",
"-CFLAGS \"-I .. -I ../obj_ref\"",
"../obj_ref/Vref__ALL.a",
@ -84,14 +85,13 @@ test.compile(verilator_flags2=[
]) # yapf:disable
test.file_grep(test.obj_dir + "/obj_opt/Vopt__stats.txt",
r'DFG pre inline Synthesis, synt / always blocks considered\s+(\d+)$',
r'DFG scoped Synthesis, synt / always blocks considered\s+(\d+)$',
nAlwaysSynthesized + nAlwaysReverted + nAlwaysNotSynthesized)
test.file_grep(test.obj_dir + "/obj_opt/Vopt__stats.txt",
r'DFG pre inline Synthesis, synt / always blocks synthesized\s+(\d+)$',
r'DFG scoped Synthesis, synt / always blocks synthesized\s+(\d+)$',
nAlwaysSynthesized + nAlwaysReverted)
test.file_grep(test.obj_dir + "/obj_opt/Vopt__stats.txt",
r'DFG pre inline Synthesis, synt / reverted \(multidrive\)\s+(\d)$',
nAlwaysReverted)
r'DFG scoped Synthesis, synt / reverted \(multidrive\)\s+(\d)$', nAlwaysReverted)
# Execute test to check equivalence
test.execute(executable=test.obj_dir + "/obj_opt/Vopt")

277
test_regress/t/t_dfg_synthesis.v
View File

@ -154,6 +154,176 @@ module t (
end
`signal(CONDITONAL_F, condigional_f);
logic [2:0] conditional_g;
always_comb begin
if (rand_a[0]) begin
if (rand_a[1]) begin
if (rand_a[2]) begin
conditional_g = 3'b111;
end else begin
conditional_g = 3'b011;
end
end else begin
if (rand_a[2]) begin
conditional_g = 3'b101;
end else begin
conditional_g = 3'b001;
end
end
end else begin
if (rand_a[1]) begin
if (rand_a[2]) begin
conditional_g = 3'b110;
end else begin
conditional_g = 3'b010;
end
end else begin
if (rand_a[2]) begin
conditional_g = 3'b100;
end else begin
conditional_g = 3'b000;
end
end
end
end
`signal(CONDITONAL_G, conditional_g);
logic [2:0] conditional_h;
always_comb begin
if (rand_a[0]) begin
if (rand_a[1]) begin
conditional_h = 3'b011;
if (rand_a[2]) begin
conditional_h = 3'b111;
end
end else begin
conditional_h = 3'b001;
if (rand_a[2]) begin
conditional_h = 3'b101;
end
end
end else begin
if (rand_a[1]) begin
conditional_h = 3'b010;
if (rand_a[2]) begin
conditional_h = 3'b110;
end
end else begin
conditional_h = 3'b000;
if (rand_a[2]) begin
conditional_h = 3'b100;
end
end
end
end
`signal(CONDITONAL_H, conditional_h);
logic [2:0] conditional_i;
always_comb begin // Dumbass trailing zeroes count
do begin
conditional_i = 3'd0;
if (rand_a[0]) break;
conditional_i = 3'd1;
if (rand_a[1]) break;
conditional_i = 3'd2;
if (rand_a[2]) break;
conditional_i = 3'd3;
if (rand_a[3]) break;
conditional_i = 3'd4;
end while (0);
end
`signal(CONDITONAL_I, conditional_i);
logic [2:0] conditional_j;
always_comb begin // Even more dumbass trailing ones count
do begin
conditional_j = 3'd0;
if (rand_a[0]) begin
conditional_j = 3'd1;
end else begin
break;
end
if (rand_a[1]) begin
conditional_j = 3'd2;
end else begin
break;
end
if (rand_a[2]) begin
conditional_j = 3'd3;
end else begin
break;
end
if (rand_a[3]) begin
conditional_j = 3'd4;
end
end while (0);
end
`signal(CONDITONAL_J, conditional_j);
logic [2:0] conditional_k;
always_comb begin
if (rand_b[0]) begin
do begin
conditional_k = 3'd0;
if (rand_a[0]) break;
conditional_k = 3'd1;
if (rand_a[1]) break;
conditional_k = 3'd2;
if (rand_a[2]) break;
conditional_k = 3'd3;
if (rand_a[3]) break;
conditional_k = 3'd4;
end while (0);
end else begin
do begin
conditional_k = 3'd0;
if (rand_a[0]) begin
conditional_k = 3'd1;
end else begin
break;
end
if (rand_a[1]) begin
conditional_k = 3'd2;
end else begin
break;
end
if (rand_a[2]) begin
conditional_k = 3'd3;
end else begin
break;
end
if (rand_a[3]) begin
conditional_k = 3'd4;
end
end while (0);
end
end
`signal(CONDITONAL_K, conditional_k);
logic [1:0] conditional_l_a;
logic [1:0] conditional_l_b;
always_comb begin
do begin
conditional_l_a = 2'd0;
if (rand_a[1:0] == 2'd0) break;
conditional_l_a = 2'd1;
if (rand_a[1:0] == 2'd1) break;
conditional_l_a = 2'd2;
if (rand_a[1:0] == 2'd2) break;
conditional_l_a = 2'd3;
end while (0);
do begin
conditional_l_b = 2'd0;
if (rand_b[1:0] == 2'd0) break;
conditional_l_b = 2'd1;
if (rand_b[1:0] == 2'd1) break;
conditional_l_b = 2'd2;
if (rand_b[1:0] == 2'd2) break;
conditional_l_b = 2'd3;
end while (0);
end
`signal(CONDITONAL_L, {conditional_l_b, conditional_l_a});
logic [7:0] partial_conditional_a;
always_comb begin
partial_conditional_a[1:0] = 2'd0;
@ -225,4 +395,111 @@ module t (
partial_temporary_a = partial_temporary_tmp;
end
`signal(PARTIAL_TEMPORARY, partial_temporary_a);
logic circular_0_x;
logic circular_0_y;
logic circular_0_z;
always_comb begin
circular_0_x = 1'b0;
circular_0_y = 1'd0;
if (rand_b[0]) begin
circular_0_x = 1'b1;
if (circular_0_z) begin
circular_0_y = 1'd1;
end
end
end
assign circular_0_z = circular_0_x & rand_a[0];
`signal(CIRCULAR_0, {circular_0_x, circular_0_y, circular_0_z});
logic [2:0] nsp_a; // Non series-parallel CFG
always_comb begin
do begin
nsp_a = 3'd0; // BB 0 -> BB 1 / BB 2
if (rand_a[1:0] == 2'd0) begin
nsp_a = 3'd1; // BB 1 -> BB 4
end else begin
nsp_a = 3'd2; // BB 2 -> BB 3 / BB 4
if (rand_a[1:0] == 2'd1) begin
nsp_a = 3'd3; // BB3 -> BB 5
break;
end
end
nsp_a = 3'd4; // BB 4 -> BB 5
end while (0);
//nsp_a = 3'd5; // BB 5
end
`signal(NSP_A, nsp_a);
logic [2:0] nsp_b; // Non series-parallel CFG
always_comb begin
do begin
nsp_b = 3'd0;
if (rand_a[1:0] == 2'd0) begin
nsp_b = 3'd1;
end else begin
nsp_b = 3'd2;
if (rand_a[1:0] == 2'd1) begin
nsp_b = 3'd3;
break;
end else begin
nsp_b = 3'd4;
if (rand_a[1:0] == 2'd2) begin
nsp_b = 3'd5;
end else begin
nsp_b = 3'd6;
break;
end
end
end
nsp_b = 3'd7;
end while (0);
end
`signal(NSP_B, nsp_b);
logic [2:0] part_sp_a; // Contains series-parallel sub-graph CFG
always_comb begin
do begin
part_sp_a = 3'd0;
if (rand_a[0]) begin
part_sp_a = 3'd1;
if (rand_a[1]) begin
part_sp_a = 3'd2;
end
end else begin
part_sp_a = 3'd3;
if (rand_a[2]) begin
part_sp_a = 3'd4;
if (rand_a[3]) begin
part_sp_a = 3'd5;
end
break;
end
end
part_sp_a = 3'd6;
if (rand_a[4]) begin
part_sp_a = 3'd7;
end
end while (0);
end
`signal(PART_SP_A, part_sp_a);
logic [1:0] both_break;
always_comb begin
do begin
if (rand_a[0]) begin
both_break = 2'd0;
break;
end else begin
both_break = 2'd1;
break;
end
// Unreachable
if (rand_a[1]) begin
both_break = 2'd2;
end
end while(0);
end
`signal(BOTH_BREAK, both_break);
endmodule