nickdesaulniers added a comment.
In D146466#4217363 <https://reviews.llvm.org/D146466#4217363>, @efriedma wrote:
> There are limits to how much we can do by just changing the code clang
> generates... but the two particular cases you mention probably could be
> "fixed" by messing with the IR generated by clang. Sure, that probably makes
> sense to pursue. (If you're going to pick an arbitrary value, zero is
> probably a better choice than "freeze poison".)
I don't think that could be a clang codegen of IR change. What I had in mind
is closer to:
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 916c02692823..aa1f288b51ee 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -236,9 +236,17 @@ void llvm::simplifyLoopAfterUnroll(Loop *L, bool
SimplifyIVs, LoopInfo *LI,
SmallVector<WeakTrackingVH, 16> DeadInsts;
for (BasicBlock *BB : L->getBlocks()) {
for (Instruction &Inst : llvm::make_early_inc_range(*BB)) {
- if (Value *V = simplifyInstruction(&Inst, {DL, nullptr, DT, AC}))
- if (LI->replacementPreservesLCSSAForm(&Inst, V))
+ if (Value *V = simplifyInstruction(&Inst, {DL, nullptr, DT, AC})) {
+ // TODO: check if sanitizer is enabled
+ if (isa<PoisonValue>(V) && isa<LoadInst>(Inst)) {
+ errs() << "XXX: found poison (replacing a load)!\n";
+ FreezeInst *FI = new FreezeInst(V);
+ FI->insertInto(BB, Inst.getIterator());
+ if (LI->replacementPreservesLCSSAForm(FI, V))
+ Inst.replaceAllUsesWith(FI);
+ } else if (LI->replacementPreservesLCSSAForm(&Inst, V))
Inst.replaceAllUsesWith(V);
+ }
if (isInstructionTriviallyDead(&Inst))
DeadInsts.emplace_back(&Inst);
}
Which seems to do exactly what I want (minus only doing so when
`-fsanitize=array-bounds` is enabled; not sure we leave such breadcrumbs behind
in IR; still looking to see if we can tell in LLVM when specific sanitizers are
enabled)
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D146466/new/
https://reviews.llvm.org/D146466
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