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JIT: Filter out a few more phi args in VN (#94699)

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I realized we could be a bit more precise when VN'ing phis.
This commit is contained in:
Jakob Botsch Nielsen 2023-11-14 19:10:37 +01:00 • committed by GitHub
parent 6ffa54863c
commit f44b4d17c4
Signed by: github
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 17 additions and 19 deletions
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36
src/coreclr/jit/valuenum.cpp
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@ -9674,19 +9674,24 @@ public:
}
//------------------------------------------------------------------------
// IsReachableFromPred: Check if a block is reachability from one of its
// predecessors.
// IsReachableThroughPred: Check if a block can be reached through one of
// its direct predecessors.
//
// Parameters:
// block - A block
// predBlock - A predecessor of 'block'
//
// Returns:
// False if 'block' is definitely not reachable even though it is a
// direct successor of 'predBlock'.
// False if 'block' is definitely not reachable through 'predBlock', even
// though it is a direct successor of 'predBlock'.
//
bool IsReachableFromPred(BasicBlock* block, BasicBlock* predBlock)
bool IsReachableThroughPred(BasicBlock* block, BasicBlock* predBlock)
{
if (!IsReachable(predBlock))
{
return false;
}
if (!predBlock->KindIs(BBJ_COND) || predBlock->JumpsToNext())
{
return true;
@ -9856,20 +9861,13 @@ PhaseStatus Compiler::fgValueNumber()
for (FlowEdge* pred = BlockPredsWithEH(block); pred != nullptr; pred = pred->getNextPredEdge())
{
BasicBlock* predBlock = pred->getSourceBlock();
if (!vs.IsReachable(predBlock))
if (!vs.IsReachableThroughPred(block, predBlock))
{
JITDUMP(" " FMT_BB " is an unreachable pred\n", predBlock->bbNum);
JITDUMP(" Unreachable through pred " FMT_BB "\n", predBlock->bbNum);
continue;
}
if (!vs.IsReachableFromPred(block, predBlock))
{
JITDUMP(" " FMT_BB " is a reachable pred, but " FMT_BB " is not reachable from it\n",
predBlock->bbNum, block->bbNum);
continue;
}
JITDUMP(" " FMT_BB " is a reachable pred\n", predBlock->bbNum);
JITDUMP(" Reachable through pred " FMT_BB "\n", predBlock->bbNum);
anyPredReachable = true;
break;
}
@ -9911,10 +9909,10 @@ void Compiler::fgValueNumberBlock(BasicBlock* blk)
for (GenTreePhi::Use& use : phiNode->Uses())
{
GenTreePhiArg* phiArg = use.GetNode()->AsPhiArg();
if (!vnState->IsReachable(phiArg->gtPredBB))
if (!vnState->IsReachableThroughPred(blk, phiArg->gtPredBB))
{
JITDUMP(" Phi arg [%06u] refers to unreachable pred " FMT_BB "\n", dspTreeID(phiArg),
phiArg->gtPredBB->bbNum);
JITDUMP(" Phi arg [%06u] is unnecessary; path through pred " FMT_BB " cannot be taken\n",
dspTreeID(phiArg), phiArg->gtPredBB->bbNum);
if ((use.GetNext() != nullptr) || (phiVNP.GetLiberal() != ValueNumStore::NoVN))
{
@ -9922,7 +9920,7 @@ void Compiler::fgValueNumberBlock(BasicBlock* blk)
}
assert(!vnState->IsReachable(blk));
JITDUMP(" ..but all preds are unreachable, so we are using it anyway\n");
JITDUMP(" ..but no other path can, so we are using it anyway\n");
}
ValueNum phiArgSsaNumVN = vnStore->VNForIntCon(phiArg->GetSsaNum());