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[SelectionDAG] Make sorting predicate stronger to remove non-deterministic ordering

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Summary:
Recommitting this with the correct sorting predicate. The Low field of Clusters is a ConstantInt and
cannot be directly compared. So we needed to invoke slt (signed less than) to compare correctly.

This fixes failures in the following tests uncovered by D39245:

LLVM :: CodeGen/ARM/ifcvt3.ll
LLVM :: CodeGen/ARM/switch-minsize.ll
LLVM :: CodeGen/X86/switch.ll
LLVM :: CodeGen/X86/switch-bt.ll
LLVM :: CodeGen/X86/switch-density.ll

Reviewers: hans, fhahn

Reviewed By: hans

Subscribers: aemerson, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D40541

llvm-svn: 319210
This commit is contained in:
Mandeep Singh Grang 2017-11-28 19:55:54 +00:00
parent 8b94bfe4a5
commit 4adb0a62b6
1 changed files with 11 additions and 4 deletions
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15
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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@ -9350,10 +9350,12 @@ bool SelectionDAGBuilder::buildBitTests(CaseClusterVector &Clusters,
BitTestInfo BTI;
std::sort(CBV.begin(), CBV.end(), [](const CaseBits &a, const CaseBits &b) {
// Sort by probability first, number of bits second.
// Sort by probability first, number of bits second, bit mask third.
if (a.ExtraProb != b.ExtraProb)
return a.ExtraProb > b.ExtraProb;
return a.Bits > b.Bits;
if (a.Bits != b.Bits)
return a.Bits > b.Bits;
return a.Mask < b.Mask;
});
for (auto &CB : CBV) {
@ -9542,10 +9544,15 @@ void SelectionDAGBuilder::lowerWorkItem(SwitchWorkListItem W, Value *Cond,
}
if (TM.getOptLevel() != CodeGenOpt::None) {
// Order cases by probability so the most likely case will be checked first.
// Here, we order cases by probability so the most likely case will be
// checked first. However, two clusters can have the same probability in
// which case their relative ordering is non-deterministic. So we use Low
// as a tie-breaker as clusters are guaranteed to never overlap.
std::sort(W.FirstCluster, W.LastCluster + 1,
[](const CaseCluster &a, const CaseCluster &b) {
return a.Prob > b.Prob;
return a.Prob != b.Prob ?
a.Prob > b.Prob :
a.Low->getValue().slt(b.Low->getValue());
});
// Rearrange the case blocks so that the last one falls through if possible