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[CodeGen] Compute DT/LI lazily in SafeStackLegacyPass. NFC.

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We currently require SCEV, which requires DT/LI.  Those are expensive to
compute, but the pass only runs for functions that have the safestack
attribute.

Compute DT/LI to build SCEV lazily, only when the pass is actually going
to transform the function.

Differential Revision: https://reviews.llvm.org/D31302

llvm-svn: 302610
This commit is contained in:
Ahmed Bougacha 2017-05-10 00:39:25 +00:00
parent 00d6822278
commit 8c358e3016
2 changed files with 15 additions and 5 deletions
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17
llvm/lib/CodeGen/SafeStack.cpp
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@ -774,7 +774,8 @@ public:
SafeStackLegacyPass() : SafeStackLegacyPass(nullptr) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<AssumptionCacheTracker>();
}
bool runOnFunction(Function &F) override {
@ -799,7 +800,19 @@ public:
report_fatal_error("TargetLowering instance is required");
auto *DL = &F.getParent()->getDataLayout();
auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
// Compute DT and LI only for functions that have the attribute.
// This is only useful because the legacy pass manager doesn't let us
// compute analyzes lazily.
// In the backend pipeline, nothing preserves DT before SafeStack, so we
// would otherwise always compute it wastefully, even if there is no
// function with the safestack attribute.
DominatorTree DT(F);
LoopInfo LI(DT);
ScalarEvolution SE(F, TLI, ACT, DT, LI);
return SafeStack(F, *TL, *DL, SE).run();
}

3
llvm/test/CodeGen/X86/O0-pipeline.ll
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@ -27,9 +27,6 @@
; CHECK-NEXT: FunctionPass Manager
; CHECK-NEXT: Dominator Tree Construction
; CHECK-NEXT: Exception handling preparation
; CHECK-NEXT: Dominator Tree Construction
; CHECK-NEXT: Natural Loop Information
; CHECK-NEXT: Scalar Evolution Analysis
; CHECK-NEXT: Safe Stack instrumentation pass
; CHECK-NEXT: Insert stack protectors
; CHECK-NEXT: Module Verifier