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Fix really obscure bug in CannotBeNegativeZero() (PR22688)

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With a diabolically crafted test case, we could recurse
through this code and return true instead of false.

The larger engineering crime is the use of magic numbers. 
Added FIXME comments for those.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230515 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel
2015-02-25 18:00:15 +00:00
parent 4454339f09
commit d2c64e2df9
2 changed files with 33 additions and 1 deletions
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8
lib/Analysis/ValueTracking.cpp
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@ -2000,8 +2000,11 @@ bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegZero();
// FIXME: Magic number! At the least, this should be given a name because it's
// used similarly in CannotBeOrderedLessThanZero(). A better fix may be to
// expose it as a parameter, so it can be used for testing / experimenting.
if (Depth == 6)
return 1; // Limit search depth.
return false; // Limit search depth.
const Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
@ -2048,6 +2051,9 @@ bool llvm::CannotBeOrderedLessThanZero(const Value *V, unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero();
// FIXME: Magic number! At the least, this should be given a name because it's
// used similarly in CannotBeNegativeZero(). A better fix may be to
// expose it as a parameter, so it can be used for testing / experimenting.
if (Depth == 6)
return false; // Limit search depth.