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InstCombine: Fix a potential bug in 0 - (X sdiv C) -> (X sdiv -C)

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While *most* (X sdiv 1) operations will get caught by InstSimplify, it
is still possible for a sdiv to appear in the worklist which hasn't been
simplified yet.

This means that it is possible for 0 - (X sdiv 1) to get transformed
into (X sdiv -1); dividing by -1 can make the transform produce undef
values instead of the proper result.

Sorry for the lack of testcase, it's a bit problematic because it relies
on the exact order of operations in the worklist.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215818 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-08-16 09:23:42 +00:00
parent cb698b26a1
commit 3bbb4b15ae
3 changed files with 26 additions and 1 deletions
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22
lib/IR/Constants.cpp
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@ -107,6 +107,28 @@ bool Constant::isAllOnesValue() const {
return false;
}
bool Constant::isOneValue() const {
// Check for 1 integers
if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))
return CI->isOne();
// Check for FP which are bitcasted from 1 integers
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
return CFP->getValueAPF().bitcastToAPInt() == 1;
// Check for constant vectors which are splats of 1 values.
if (const ConstantVector *CV = dyn_cast<ConstantVector>(this))
if (Constant *Splat = CV->getSplatValue())
return Splat->isOneValue();
// Check for constant vectors which are splats of 1 values.
if (const ConstantDataVector *CV = dyn_cast<ConstantDataVector>(this))
if (Constant *Splat = CV->getSplatValue())
return Splat->isOneValue();
return false;
}
bool Constant::isMinSignedValue() const {
// Check for INT_MIN integers
if (const ConstantInt *CI = dyn_cast<ConstantInt>(this))