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Optimize large lookup tables to static data (#2926)

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Implements #2925
This commit is contained in:
Geza Lore
2021-05-08 20:04:56 +01:00
committed by GitHub
parent 37d68d39c8
commit f6c0108c86
10 changed files with 300 additions and 36 deletions
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src/V3Premit.cpp
+71 -26
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@@ -30,17 +30,21 @@
#include "V3Global.h"
#include "V3Premit.h"
#include "V3Ast.h"
#include "V3Hashed.h"
#include "V3Stats.h"
#include <algorithm>
constexpr int STATIC_CONST_MIN_WIDTH = 256; // Minimum size to extract to static constant
//######################################################################
// Structure for global state
class PremitAssignVisitor final : public AstNVisitor {
private:
// NODE STATE
// AstVar::user4() // bool; occurs on LHS of current assignment
AstUser4InUse m_inuser4;
// AstVar::user3() // bool; occurs on LHS of current assignment
AstUser3InUse m_inuser3;
// STATE
bool m_noopt = false; // Disable optimization of variables in this block
@@ -50,7 +54,7 @@ private:
// VISITORS
virtual void visit(AstNodeAssign* nodep) override {
// AstNode::user4ClearTree(); // Implied by AstUser4InUse
// AstNode::user3ClearTree(); // Implied by AstUser3InUse
// LHS first as fewer varrefs
iterateAndNextNull(nodep->lhsp());
// Now find vars marked as lhs
@@ -59,9 +63,9 @@ private:
virtual void visit(AstVarRef* nodep) override {
// it's LHS var is used so need a deep temporary
if (nodep->access().isWriteOrRW()) {
nodep->varp()->user4(true);
nodep->varp()->user3(true);
} else {
if (nodep->varp()->user4()) {
if (nodep->varp()->user3()) {
if (!m_noopt) UINFO(4, "Block has LHS+RHS var: " << nodep << endl);
m_noopt = true;
}
@@ -88,9 +92,11 @@ private:
// AstNodeMath::user() -> bool. True if iterated already
// AstShiftL::user2() -> bool. True if converted to conditional
// AstShiftR::user2() -> bool. True if converted to conditional
// AstConst::user2p() -> Replacement static variable pointer
// *::user4() -> See PremitAssignVisitor
AstUser1InUse m_inuser1;
AstUser2InUse m_inuser2;
// AstUser4InUse part of V3Hashed
// STATE
AstNodeModule* m_modp = nullptr; // Current module
@@ -100,6 +106,11 @@ private:
AstTraceInc* m_inTracep = nullptr; // Inside while loop, special statement additions
bool m_assignLhs = false; // Inside assignment lhs, don't breakup extracts
V3Hashed m_hashed; // Hash set for static constants that can be reused
VDouble0 m_staticConstantsExtracted; // Statistic tracking
VDouble0 m_staticConstantsReused; // Statistic tracking
// METHODS
VL_DEBUG_FUNC; // Declare debug()
@@ -139,14 +150,6 @@ private:
}
}
AstVar* getBlockTemp(AstNode* nodep) {
string newvarname = (string("__Vtemp") + cvtToStr(m_modp->varNumGetInc()));
AstVar* varp
= new AstVar(nodep->fileline(), AstVarType::STMTTEMP, newvarname, nodep->dtypep());
m_cfuncp->addInitsp(varp);
return varp;
}
void insertBeforeStmt(AstNode* newp) {
// Insert newp before m_stmtp
if (m_inWhilep) {
@@ -173,28 +176,66 @@ private:
AstNRelinker linker;
nodep->unlinkFrBack(&linker);
AstVar* varp = getBlockTemp(nodep);
AstVar* varp = nullptr;
AstConst* const constp = VN_CAST(nodep, Const);
const bool useStatic = constp && (constp->width() >= STATIC_CONST_MIN_WIDTH)
&& !constp->num().isFourState();
if (useStatic) {
// Extract as static constant
m_hashed.hash(constp);
const auto& it = m_hashed.findDuplicate(constp);
if (it == m_hashed.end()) {
const string newvarname = string("__Vconst") + cvtToStr(m_modp->varNumGetInc());
varp = new AstVar(nodep->fileline(), AstVarType::MODULETEMP, newvarname,
nodep->dtypep());
varp->isConst(true);
varp->isStatic(true);
varp->valuep(constp);
m_modp->addStmtp(varp);
m_hashed.hashAndInsert(constp);
nodep->user2p(varp);
++m_staticConstantsExtracted;
} else {
varp = VN_CAST(it->second->user2p(), Var);
++m_staticConstantsReused;
}
} else {
// Keep as local temporary
const string newvarname = string("__Vtemp") + cvtToStr(m_modp->varNumGetInc());
varp
= new AstVar(nodep->fileline(), AstVarType::STMTTEMP, newvarname, nodep->dtypep());
m_cfuncp->addInitsp(varp);
}
if (noSubst) varp->noSubst(true); // Do not remove varrefs to this in V3Const
// Replace node tree with reference to var
AstVarRef* newp = new AstVarRef(nodep->fileline(), varp, VAccess::READ);
linker.relink(newp);
// Put assignment before the referencing statement
AstAssign* assp = new AstAssign(
nodep->fileline(), new AstVarRef(nodep->fileline(), varp, VAccess::WRITE), nodep);
insertBeforeStmt(assp);
if (debug() > 8) assp->dumpTree(cout, "deepou:");
if (!useStatic) {
// Put assignment before the referencing statement
AstAssign* assp = new AstAssign(
nodep->fileline(), new AstVarRef(nodep->fileline(), varp, VAccess::WRITE), nodep);
insertBeforeStmt(assp);
if (debug() > 8) assp->dumpTree(cout, "deepou:");
}
nodep->user1(true); // Don't add another assignment
}
// VISITORS
virtual void visit(AstNodeModule* nodep) override {
UINFO(4, " MOD " << nodep << endl);
VL_RESTORER(m_modp);
{
m_modp = nodep;
m_cfuncp = nullptr;
iterateChildren(nodep);
}
UASSERT_OBJ(m_modp == nullptr, nodep, "Nested modules ?");
UASSERT_OBJ(m_hashed.mmap().empty(), nodep, "Statements outside module ?");
m_modp = nodep;
m_cfuncp = nullptr;
iterateChildren(nodep);
m_modp = nullptr;
m_hashed.clear();
}
virtual void visit(AstCFunc* nodep) override {
VL_RESTORER(m_cfuncp);
@@ -401,7 +442,11 @@ private:
public:
// CONSTRUCTORS
explicit PremitVisitor(AstNetlist* nodep) { iterate(nodep); }
virtual ~PremitVisitor() override = default;
virtual ~PremitVisitor() {
V3Stats::addStat("Optimizations, Prelim static constants extracted",
m_staticConstantsExtracted);
V3Stats::addStat("Optimizations, Prelim static constants reused", m_staticConstantsReused);
}
};
//----------------------------------------------------------------------