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https://github.com/verilator/verilator.git
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Optimize DfgGraph vertex storage
Vertices representing variables (DfgVertexVar) and constants (DfgConst) are very common (40-50% of all vertices created in some large designs), and we also need to, or can treat them specially in algorithms. Keep these as separate lists in DfgGraph for direct access to them. This improve verilation speed.
This commit is contained in:
Geza Lore
+87
-33
@@ -84,16 +84,37 @@ void V3DfgPasses::cse(DfgGraph& dfg, V3DfgCseContext& ctx) {
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// Used by DfgVertex::hash
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const auto userDataInUse = dfg.userDataInUse();
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// In reverse, as the graph is sometimes in reverse topological order already
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for (DfgVertex *vtxp = dfg.verticesRbegin(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesPrev();
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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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}
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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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// Don't merge constants
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if (vtxp->is<DfgConst>()) continue;
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// For everything else...
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std::vector<DfgVertex*>& vec = verticesWithEqualHashes[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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@@ -109,23 +130,37 @@ void V3DfgPasses::cse(DfgGraph& dfg, V3DfgCseContext& ctx) {
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}
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}
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void V3DfgPasses::inlineVars(DfgGraph& dfg) {
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for (DfgVertexVar *vtxp = dfg.varVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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if (DfgVarPacked* const varp = vtxp->cast<DfgVarPacked>()) {
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if (varp->hasSinks() && varp->isDrivenFullyByDfg()) {
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DfgVertex* const driverp = varp->source(0);
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varp->forEachSinkEdge([=](DfgEdge& edge) { edge.relinkSource(driverp); });
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}
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}
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}
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}
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void V3DfgPasses::removeVars(DfgGraph& dfg, DfgRemoveVarsContext& ctx) {
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dfg.forEachVertex([&](DfgVertex& vtx) {
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// We can eliminate certain redundant DfgVarPacked vertices
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DfgVarPacked* const varp = vtx.cast<DfgVarPacked>();
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if (!varp) return;
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for (DfgVertexVar *vtxp = dfg.varVerticesBeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesNext();
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// We can only eliminate DfgVarPacked vertices at the moment
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DfgVarPacked* const varp = vtxp->cast<DfgVarPacked>();
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if (!varp) continue;
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// Can't remove if it has consumers
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if (varp->hasSinks()) return;
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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()) return;
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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()) return;
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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()) return;
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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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@@ -144,7 +179,7 @@ void V3DfgPasses::removeVars(DfgGraph& dfg, DfgRemoveVarsContext& ctx) {
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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) return;
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if (keepFirst && firstSinkVarp == varp) continue;
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}
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// OK, we can delete this DfgVarPacked
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@@ -155,22 +190,41 @@ void V3DfgPasses::removeVars(DfgGraph& dfg, DfgRemoveVarsContext& ctx) {
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if (!varp->hasRefs()) varp->varp()->unlinkFrBack()->deleteTree();
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// Unlink and delete vertex
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vtx.unlinkDelete(dfg);
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});
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varp->unlinkDelete(dfg);
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}
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}
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void V3DfgPasses::removeUnused(DfgGraph& dfg) {
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const auto processVertex = [&](DfgVertex& vtx) {
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// Keep variables
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if (vtx.is<DfgVertexVar>()) return false;
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// Keep if it has sinks
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if (vtx.hasSinks()) return false;
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// Unlink and delete vertex
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vtx.unlinkDelete(dfg);
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return true;
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};
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// Iteratively remove operation vertices
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while (true) {
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// Do one pass over the graph.
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bool changed = false;
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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 (!vtxp->hasSinks()) {
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changed = true;
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vtxp->unlinkDelete(dfg);
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}
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}
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if (!changed) break;
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// Do another pass in the opposite direction. Alternating directions reduces
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// the pathological complexity with left/right leaning trees.
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changed = false;
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for (DfgVertex *vtxp = dfg.opVerticesRbeginp(), *nextp; vtxp; vtxp = nextp) {
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nextp = vtxp->verticesPrev();
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if (!vtxp->hasSinks()) {
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changed = true;
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vtxp->unlinkDelete(dfg);
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}
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}
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if (!changed) break;
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}
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dfg.runToFixedPoint(processVertex);
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// Finally remove unused constants
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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 (!vtxp->hasSinks()) vtxp->unlinkDelete(dfg);
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}
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}
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void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {
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@@ -193,12 +247,12 @@ void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {
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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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if (v3Global.opt.fDfgPeephole()) {
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apply(4, "peephole ", [&]() { peephole(dfg, ctx.m_peepholeContext); });
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// Without peephole no variables will be redundant, and we just did CSE, so skip these
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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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}
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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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if (dumpDfg() >= 8) dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "optimized");
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}
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