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fix PR8753, eliminating a case where we'd infinitely make a

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substitution because it doesn't actually change the IR.  Patch by
Jakub Staszak!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121361 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2010-12-09 07:39:50 +00:00
parent d8c0536651
commit f7f35467a9
2 changed files with 24 additions and 3 deletions
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lib/Transforms/Scalar/MemCpyOptimizer.cpp
+8
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@@ -675,6 +675,14 @@ bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
if (M->getSource() != MDep->getDest() || MDep->isVolatile())
return false;
// If dep instruction is reading from our current input, then it is a noop
// transfer and substituting the input won't change this instruction. Just
// ignore the input and let someone else zap MDep. This handles cases like:
// memcpy(a <- a)
// memcpy(b <- a)
if (M->getSource() == MDep->getSource())
return false;
// Second, the length of the memcpy's must be the same, or the preceeding one
// must be larger than the following one.
ConstantInt *C1 = dyn_cast<ConstantInt>(MDep->getLength());