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https://github.com/verilator/verilator.git
synced 2026-10-06 01:54:01 +02:00
Various Dfg performance improvements
This commit is contained in:
Geza Lore
+93
-81
@@ -75,59 +75,66 @@ V3DfgOptimizationContext::~V3DfgOptimizationContext() {
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"Inconsistent statistics");
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}
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// Common subexpression elimination
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// Common sub-expression elimination
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void V3DfgPasses::cse(DfgGraph& dfg, V3DfgCseContext& ctx) {
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DfgVertex::EqualsCache equalsCache;
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std::unordered_map<V3Hash, std::vector<DfgVertex*>> verticesWithEqualHashes;
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verticesWithEqualHashes.reserve(dfg.size());
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// Remove common sub-expressions
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{
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// Used by DfgVertex::hash
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const auto userDataInUse = dfg.userDataInUse();
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// Used by DfgVertex::hash
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const auto userDataInUse = dfg.userDataInUse();
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DfgVertex::EqualsCache equalsCache;
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std::unordered_map<V3Hash, std::vector<DfgVertex*>> verticesWithEqualHashes;
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verticesWithEqualHashes.reserve(dfg.size());
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// Pre-hash variables for speed, these are all unique, so just set their hash to a unique value
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uint32_t varHash = 0;
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for (DfgVertexVar *vtxp = dfg.varVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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vtxp->user<V3Hash>() = V3Hash{++varHash};
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}
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// Similarly pre-hash constants for speed. While we don't combine constants, we do want
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// expressions using the same constants to be combined, so we do need to hash equal constants
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// to equal values.
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for (DfgConst *vtxp = dfg.constVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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// Get rid of unused constants while we are at it
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if (!vtxp->hasSinks()) {
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vtxp->unlinkDelete(dfg);
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continue;
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// Pre-hash variables, these are all unique, so just set their hash to a unique value
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uint32_t varHash = 0;
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for (DfgVertexVar *vtxp = dfg.varVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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vtxp->user<V3Hash>() = V3Hash{++varHash};
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}
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vtxp->user<V3Hash>() = vtxp->num().toHash();
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}
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// Combine operation vertices
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for (DfgVertex *vtxp = dfg.opVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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// Get rid of unused operations while we are at it
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if (!vtxp->hasSinks()) {
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vtxp->unlinkDelete(dfg);
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continue;
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}
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const V3Hash hash = vtxp->hash();
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if (VL_LIKELY(nextp)) VL_PREFETCH_RW(nextp);
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std::vector<DfgVertex*>& vec = verticesWithEqualHashes[hash];
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bool replaced = false;
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for (DfgVertex* const candidatep : vec) {
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if (candidatep->equals(*vtxp, equalsCache)) {
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++ctx.m_eliminated;
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vtxp->replaceWith(candidatep);
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// Similarly pre-hash constants for speed. While we don't combine constants, we do want
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// expressions using the same constants to be combined, so we do need to hash equal
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// constants to equal values.
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for (DfgConst *vtxp = dfg.constVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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if (VL_LIKELY(nextp)) VL_PREFETCH_RW(nextp);
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// Delete unused constants while we are at it.
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if (!vtxp->hasSinks()) {
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vtxp->unlinkDelete(dfg);
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replaced = true;
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break;
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continue;
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}
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vtxp->user<V3Hash>() = vtxp->num().toHash() + varHash;
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}
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// Combine operation vertices
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for (DfgVertex *vtxp = dfg.opVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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if (VL_LIKELY(nextp)) VL_PREFETCH_RW(nextp);
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// Delete unused nodes while we are at it.
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if (!vtxp->hasSinks()) {
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vtxp->unlinkDelete(dfg);
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continue;
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}
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const V3Hash hash = vtxp->hash();
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std::vector<DfgVertex*>& vec = verticesWithEqualHashes[hash];
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bool replaced = false;
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for (DfgVertex* const candidatep : vec) {
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if (candidatep->equals(*vtxp, equalsCache)) {
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++ctx.m_eliminated;
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vtxp->replaceWith(candidatep);
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vtxp->unlinkDelete(dfg);
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replaced = true;
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break;
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}
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}
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if (replaced) continue;
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vec.push_back(vtxp);
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}
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if (replaced) continue;
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vec.push_back(vtxp);
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}
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// Prune unused nodes
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removeUnused(dfg);
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}
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void V3DfgPasses::inlineVars(DfgGraph& dfg) {
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@@ -167,41 +174,46 @@ void V3DfgPasses::removeVars(DfgGraph& dfg, DfgRemoveVarsContext& ctx) {
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// Can't remove if it has consumers
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if (varp->hasSinks()) continue;
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// Can't remove if read in the module and driven here (i.e.: it's an output of the DFG)
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if (varp->hasModRefs() && varp->isDrivenByDfg()) continue;
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// Can't remove if only partially driven by the DFG
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if (varp->isDrivenByDfg() && !varp->isDrivenFullyByDfg()) continue;
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// Can't remove if referenced externally, or other special reasons
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if (varp->keep()) continue;
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// If the driver of this variable has multiple non-variable sinks, then we would need
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// a temporary when rendering the graph. Instead of introducing a temporary, keep the
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// first variable that is driven by that driver
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// Otherwise if it has drivers
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if (varp->isDrivenByDfg()) {
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DfgVertex* const driverp = varp->source(0);
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unsigned nonVarSinks = 0;
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const DfgVarPacked* firstSinkVarp = nullptr;
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const bool keepFirst = driverp->findSink<DfgVertex>([&](const DfgVertex& sink) {
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if (const DfgVarPacked* const sinkVarp = sink.cast<DfgVarPacked>()) {
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if (!firstSinkVarp) firstSinkVarp = sinkVarp;
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} else {
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++nonVarSinks;
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// Can't remove if read in the module and driven here (i.e.: it's an output of the DFG)
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if (varp->hasModRefs()) continue;
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// Can't remove if referenced externally, or other special reasons
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if (varp->keep()) continue;
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// If the driver of this variable is not an inlined vertex, then we would need a
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// temporary when rendering the graph. Instead of introducing a temporary, keep the
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// first variable that is driven by that driver. Note that we still remove if the only
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// sinks we have are variables, as we might be able to remove all of them (we can be
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// sure the not inlined if we have at least 2 non-variable sinks).
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if (varp->isDrivenFullyByDfg()) {
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DfgVertex* const driverp = varp->source(0);
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if (!driverp->inlined()) {
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unsigned nonVarSinks = 0;
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const DfgVarPacked* firstp = nullptr;
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const bool found = driverp->findSink<DfgVertex>([&](const DfgVertex& sink) {
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if (const DfgVarPacked* const sinkVarp = sink.cast<DfgVarPacked>()) {
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if (!firstp) firstp = sinkVarp;
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} else {
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++nonVarSinks;
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}
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// We can stop as soon as we found the first var, and 2 non-var sinks
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return firstp && nonVarSinks >= 2;
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});
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// Keep this DfgVarPacked if needed
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if (found && firstp == varp) continue;
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}
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// We can stop as soon as we found the first var, and 2 non-var sinks
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return firstSinkVarp && nonVarSinks >= 2;
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});
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// Keep this DfgVarPacked if needed
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if (keepFirst && firstSinkVarp == varp) continue;
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}
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}
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// OK, we can delete this DfgVarPacked
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++ctx.m_removed;
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// OK, we can delete this DfgVarPacked from the graph.
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// If not referenced outside the DFG, then also delete the referenced AstVar,
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// as it is now unused.
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if (!varp->hasRefs()) varp->varp()->unlinkFrBack()->deleteTree();
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// If not referenced outside the DFG, then also delete the referenced AstVar (now unused).
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if (!varp->hasRefs()) {
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++ctx.m_removed;
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varp->varp()->unlinkFrBack()->deleteTree();
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}
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// Unlink and delete vertex
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varp->unlinkDelete(dfg);
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@@ -283,14 +295,14 @@ void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {
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};
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if (dumpDfg() >= 8) dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "input");
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apply(3, "input ", [&]() {});
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apply(4, "cse ", [&]() { cse(dfg, ctx.m_cseContext0); });
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apply(4, "inlineVars ", [&]() { inlineVars(dfg); });
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apply(3, "input ", [&]() {});
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apply(4, "inlineVars ", [&]() { inlineVars(dfg); });
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apply(4, "cse0 ", [&]() { cse(dfg, ctx.m_cseContext0); });
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if (v3Global.opt.fDfgPeephole()) {
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apply(4, "peephole ", [&]() { peephole(dfg, ctx.m_peepholeContext); });
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apply(4, "peephole ", [&]() { peephole(dfg, ctx.m_peepholeContext); });
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// We just did CSE above, so without peephole there is no need to run it again these
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apply(4, "cse1 ", [&]() { cse(dfg, ctx.m_cseContext1); });
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}
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apply(4, "cse ", [&]() { cse(dfg, ctx.m_cseContext1); });
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apply(4, "removeVars ", [&]() { removeVars(dfg, ctx.m_removeVarsContext); });
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apply(3, "optimized ", [&]() { removeUnused(dfg); });
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apply(4, "removeVars ", [&]() { removeVars(dfg, ctx.m_removeVarsContext); });
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if (dumpDfg() >= 8) dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "optimized");
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}
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