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https://github.com/verilator/verilator.git
synced 2026-10-06 10:03:44 +02:00
Optimize commutative vertex operands in Dfg for better combining
This commit is contained in:
Geza Lore
+90
-28
@@ -133,6 +133,7 @@ class V3DfgPeephole final : public DfgVisitor {
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struct VertexInfo final {
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size_t m_workListIndex = 0; // Position of this vertx m_wlist (0 means not in list)
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size_t m_generation = 0; // Generation number of this vertex
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size_t m_id = 0; // Unique vertex ID (0 means unassigned)
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};
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// STATE
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@@ -144,6 +145,7 @@ class V3DfgPeephole final : public DfgVisitor {
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V3DfgCache m_cache{m_dfg}; // Vertex cache to avoid creating redundant vertices
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DfgVertex* m_vtxp = nullptr; // Currently considered vertex
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size_t m_currentGeneration = 0; // Current generation number
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size_t m_lastId = 0; // Last unique vertex ID assigned
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// STATIC STATE
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static V3DebugBisect s_debugBisect; // Debug aid
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@@ -303,6 +305,9 @@ class V3DfgPeephole final : public DfgVisitor {
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// Sanity check
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UASSERT_OBJ(vtxp->dtype() == dtype, vtxp, "Vertex dtype mismatch");
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if (VL_UNLIKELY(v3Global.opt.debugCheck())) vtxp->typeCheck(m_dfg);
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// Assign vertex ID
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VertexInfo& vInfo = m_vInfo[vtxp];
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if (!vInfo.m_id) vInfo.m_id = ++m_lastId;
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// Add to work list
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addToWorkList(vtxp);
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// Return new node
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@@ -457,17 +462,40 @@ class V3DfgPeephole final : public DfgVisitor {
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}
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}
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// if (a OP (b OP c)), check if (a OP b) exists and if so replace with (a OP b) OP c
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if (Vertex* rVtxp = vtxp->rhsp()->template cast<Vertex>()) {
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const DfgDataType& dtype
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= std::is_same<Vertex, DfgConcat>::value
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? DfgDataType::packed(lhsp->width() + rVtxp->lhsp()->width())
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: vtxp->dtype();
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if (Vertex* const cVtxp = m_cache.get<Vertex>(dtype, lhsp, rVtxp->lhsp())) {
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if (cVtxp->hasSinks() && cVtxp != rhsp) {
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APPLYING(REUSE_ASSOC_BINARY) {
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replace(make<Vertex>(vtxp, cVtxp, rVtxp->rhsp()));
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return true;
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// Attempt to reuse associative binary expressions if hey already exist, e.g.:
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// '(a OP (b OP c))' -> '(a OP b) OP c', iff '(a OP b)' already exists, or
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// '(a OP c) OP b' iff '(a OP c)' already exists and the vertex is commutative.
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// Only do this is 'b OP c' has a single use and can subsequently be removed,
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// otherwise there is no improvement.
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if (!rhsp->hasMultipleSinks()) {
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if (Vertex* rVtxp = rhsp->template cast<Vertex>()) {
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DfgVertex* const rlVtxp = rVtxp->lhsp();
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DfgVertex* const rrVtxp = rVtxp->rhsp();
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const DfgDataType& dtype
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= std::is_same<Vertex, DfgConcat>::value
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? DfgDataType::packed(lhsp->width() + rlVtxp->width())
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: vtxp->dtype();
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if (Vertex* const existingp = m_cache.get<Vertex>(dtype, lhsp, rlVtxp)) {
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UASSERT_OBJ(existingp->hasSinks(), vtxp, "Existing vertex should be used");
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if (existingp != rhsp) {
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APPLYING(REUSE_ASSOC_BINARY_LHS_WITH_LHS_OF_RHS) {
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replace(make<Vertex>(vtxp, existingp, rrVtxp));
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return true;
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}
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}
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}
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// Concat is not commutative
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if VL_CONSTEXPR_CXX17 (!std::is_same<Vertex, DfgConcat>::value) {
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if (Vertex* const existingp = m_cache.get<Vertex>(dtype, lhsp, rrVtxp)) {
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UASSERT_OBJ(existingp->hasSinks(), vtxp, "Existing vertex should be used");
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if (existingp != rhsp) {
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APPLYING(REUSE_ASSOC_BINARY_LHS_WITH_RHS_OF_RHS) {
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replace(make<Vertex>(vtxp, existingp, rlVtxp));
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return true;
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}
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}
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}
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}
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}
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@@ -484,29 +512,59 @@ class V3DfgPeephole final : public DfgVisitor {
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DfgVertex* const lhsp = vtxp->lhsp();
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DfgVertex* const rhsp = vtxp->rhsp();
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// Ensure Const is on left-hand side to simplify other patterns
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if (lhsp->is<DfgConst>()) return false;
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if (rhsp->is<DfgConst>()) {
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APPLYING(SWAP_CONST_IN_COMMUTATIVE_BINARY) {
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replace(make<Vertex>(vtxp, rhsp, lhsp));
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return true;
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{
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const bool lIsConst = lhsp->is<DfgConst>();
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const bool rIsConst = rhsp->is<DfgConst>();
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if (lIsConst != rIsConst) {
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if (rIsConst) {
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APPLYING(SWAP_CONST_IN_COMMUTATIVE_BINARY) {
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replace(make<Vertex>(vtxp, rhsp, lhsp));
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return true;
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}
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}
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return false;
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}
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}
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// Ensure Not is on the left-hand side to simplify other patterns
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if (lhsp->is<DfgNot>()) return false;
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if (rhsp->is<DfgNot>()) {
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APPLYING(SWAP_NOT_IN_COMMUTATIVE_BINARY) {
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replace(make<Vertex>(vtxp, rhsp, lhsp));
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return true;
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{
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const bool lIsNot = lhsp->is<DfgNot>();
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const bool rIsNot = rhsp->is<DfgNot>();
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if (lIsNot != rIsNot) {
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if (rIsNot) {
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APPLYING(SWAP_NOT_IN_COMMUTATIVE_BINARY) {
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replace(make<Vertex>(vtxp, rhsp, lhsp));
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return true;
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}
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}
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return false;
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}
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}
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// If both sides are variable references, order the side in some defined way. This
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// allows CSE to later merge 'a op b' with 'b op a'.
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if (lhsp->is<DfgVertexVar>() && rhsp->is<DfgVertexVar>()) {
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const AstNode* const lVarp = lhsp->as<DfgVertexVar>()->nodep();
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const AstNode* const rVarp = rhsp->as<DfgVertexVar>()->nodep();
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if (lVarp->name() > rVarp->name()) {
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APPLYING(SWAP_VAR_IN_COMMUTATIVE_BINARY) {
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// Ensure same vertex is on the right-hand side to simplify other patterns
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{
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const bool lIsSame = lhsp->is<Vertex>();
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const bool rIsSame = rhsp->is<Vertex>();
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if (lIsSame != rIsSame) {
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if (lIsSame) {
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APPLYING(SWAP_SAME_IN_COMMUTATIVE_BINARY) {
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replace(make<Vertex>(vtxp, rhsp, lhsp));
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return true;
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}
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}
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return false;
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}
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}
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// Otherwise put sides in order based on unique iD, this makes
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// 'a op b' and 'b op a' end up the same for better combining.
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{
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const VertexInfo& lInfo = m_vInfo[lhsp];
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const VertexInfo& rInfo = m_vInfo[rhsp];
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if (lInfo.m_id > rInfo.m_id) {
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APPLYING(SWAP_SIDE_IN_COMMUTATIVE_BINARY) {
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replace(make<Vertex>(vtxp, rhsp, lhsp));
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return true;
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}
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@@ -1443,6 +1501,7 @@ class V3DfgPeephole final : public DfgVisitor {
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DfgVertex::ScopeCache scopeCache;
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DfgSplicePacked* const sp = new DfgSplicePacked{m_dfg, flp, vtxp->dtype()};
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sp->addDriver(catp, lsb, flp);
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m_vInfo[sp].m_id = ++m_lastId;
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replace(sp);
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return;
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}
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@@ -1860,6 +1919,9 @@ class V3DfgPeephole final : public DfgVisitor {
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: m_dfg{dfg}
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, m_ctx{ctx} {
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// Assign vertex IDs
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m_dfg.forEachVertex([&](DfgVertex& vtx) { m_vInfo[vtx].m_id = ++m_lastId; });
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// Initialize the work list
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m_wlist.reserve(m_dfg.size() * 4);
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@@ -107,13 +107,15 @@
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, REPLACE_WITH_EQUIVALENT) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, REPLACE_XOR_WITH_ONES) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, REPLACE_XOR_WITH_SELF) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, REUSE_ASSOC_BINARY) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, REUSE_ASSOC_BINARY_LHS_WITH_LHS_OF_RHS) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, REUSE_ASSOC_BINARY_LHS_WITH_RHS_OF_RHS) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, RIGHT_LEANING_ASSOC) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_COND_WITH_NEQ_CONDITION) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_COND_WITH_NOT_CONDITION) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_CONST_IN_COMMUTATIVE_BINARY) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_NOT_IN_COMMUTATIVE_BINARY) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_VAR_IN_COMMUTATIVE_BINARY)
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_NOT_IN_COMMUTATIVE_BINARY) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_SAME_IN_COMMUTATIVE_BINARY) \
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_FOR_EACH_DFG_PEEPHOLE_OPTIMIZATION_APPLY(macro, SWAP_SIDE_IN_COMMUTATIVE_BINARY)
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// clang-format on
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class VDfgPeepholePattern final {
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