luke/verilator
1
0
Fork 0
mirror of https://github.com/verilator/verilator.git synced 2026-10-06 01:54:01 +02:00
Code Issues Packages Projects Releases Wiki Activity

DFG: make variable inlining part of the peephole optimizer

Browse Source 
This saves some traversals and prepares us to better handle cyclic DFGs.
This commit is contained in:
Geza Lore
2022-09-29 18:40:10 +01:00
parent 09e352ef66
commit 4a1a2def95
4 changed files with 37 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/V3DfgPasses.cpp
+8 -40
View File
@@ -75,20 +75,6 @@ V3DfgOptimizationContext::~V3DfgOptimizationContext() {
"Inconsistent statistics");
}
// 'Inline' DfgVar nodes with known drivers
void V3DfgPasses::inlineVars(DfgGraph& dfg) {
dfg.forEachVertex([](DfgVertex& vtx) {
// For each DfgVar that has a known driver
if (DfgVar* const varVtxp = vtx.cast<DfgVar>()) {
if (varVtxp->isDrivenFullyByDfg()) {
// Make consumers of the DfgVar consume the driver directly
DfgVertex* const driverp = varVtxp->source(0);
varVtxp->forEachSinkEdge([=](DfgEdge& edge) { edge.relinkSource(driverp); });
}
}
});
}
// Common subexpression elimination
void V3DfgPasses::cse(DfgGraph& dfg, V3DfgCseContext& ctx) {
DfgVertex::HashCache hashCache;
@@ -183,16 +169,6 @@ void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {
// There is absolutely nothing useful we can do with a graph of size 2 or less
if (dfg.size() <= 2) return;
// We consider a DFG trivial if it contains no more than 1 non-variable, non-constant vertex,
// or if if it contains a DfgConcat, which can be introduced through assinment coalescing.
unsigned excitingVertices = 0;
const bool isTrivial = !dfg.findVertex<DfgVertex>([&](const DfgVertex& vtx) { //
if (vtx.is<DfgVar>()) return false;
if (vtx.is<DfgConst>()) return false;
if (vtx.is<DfgConcat>()) return true;
return ++excitingVertices >= 2;
});
int passNumber = 0;
const auto apply = [&](int dumpLevel, const string name, std::function<void()> pass) {
@@ -206,23 +182,15 @@ void V3DfgPasses::optimize(DfgGraph& dfg, V3DfgOptimizationContext& ctx) {
++passNumber;
};
if (!isTrivial) {
// Optimize non-trivial graph
if (dumpDfg() >= 8) { dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "input"); }
apply(3, "input ", [&]() {});
apply(4, "inlineVars ", [&]() { inlineVars(dfg); });
apply(4, "cse ", [&]() { cse(dfg, ctx.m_cseContext0); });
if (v3Global.opt.fDfgPeephole()) {
apply(4, "peephole ", [&]() { peephole(dfg, ctx.m_peepholeContext); });
}
if (dumpDfg() >= 8) dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "input");
apply(3, "input ", [&]() {});
apply(4, "cse ", [&]() { cse(dfg, ctx.m_cseContext0); });
if (v3Global.opt.fDfgPeephole()) {
apply(4, "peephole ", [&]() { peephole(dfg, ctx.m_peepholeContext); });
// Without peephole no variables will be redundant, and we just did CSE, so skip these
apply(4, "removeVars ", [&]() { removeVars(dfg, ctx.m_removeVarsContext); });
apply(4, "cse ", [&]() { cse(dfg, ctx.m_cseContext1); });
apply(3, "optimized ", [&]() { removeUnused(dfg); });
if (dumpDfg() >= 8) { dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "optimized"); }
} else {
// We can still eliminate redundancies from trivial graphs
apply(5, "trivial-input ", [&]() {});
apply(6, "trivial-inlineVars ", [&]() { inlineVars(dfg); });
apply(5, "trivial-optimized ", [&]() { removeVars(dfg, ctx.m_removeVarsContext); });
}
apply(3, "optimized ", [&]() { removeUnused(dfg); });
if (dumpDfg() >= 8) dfg.dumpDotAllVarConesPrefixed(ctx.prefix() + "optimized");
}