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[SimplifyCFG] Make range reduction code deterministic.

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This generated IR based on the order of evaluation, which is different
between GCC and Clang. With that in mind you get bootstrap miscompares
if you compare a Clang built with GCC-built Clang vs. Clang built with
Clang-built Clang. Diagnosing that made my head hurt.

This also reverts commit r277337, which "fixed" the test case.

llvm-svn: 277820
This commit is contained in:
Benjamin Kramer
2016-08-05 14:55:02 +00:00
parent 5a9b9f98c0
commit aa160c22f7
2 changed files with 23 additions and 22 deletions
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5
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@@ -5128,8 +5128,9 @@ static bool ReduceSwitchRange(SwitchInst *SI, IRBuilder<> &Builder,
Builder.SetInsertPoint(SI);
auto *ShiftC = ConstantInt::get(Ty, Shift);
auto *Sub = Builder.CreateSub(SI->getCondition(), ConstantInt::get(Ty, Base));
auto *Rot = Builder.CreateOr(Builder.CreateLShr(Sub, ShiftC),
Builder.CreateShl(Sub, Ty->getBitWidth() - Shift));
auto *LShr = Builder.CreateLShr(Sub, ShiftC);
auto *Shl = Builder.CreateShl(Sub, Ty->getBitWidth() - Shift);
auto *Rot = Builder.CreateOr(LShr, Shl);
SI->replaceUsesOfWith(SI->getCondition(), Rot);
for (SwitchInst::CaseIt C = SI->case_begin(), E = SI->case_end(); C != E;