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Add a missing safety check to ProcessUGT_ADDCST_ADD. Fixes PR11438.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145316 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman
2011-11-28 23:32:19 +00:00
parent 4544da484d
commit 54b92113e2
2 changed files with 30 additions and 0 deletions
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lib/Transforms/InstCombine/InstCombineCompares.cpp
+8
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@@ -1657,6 +1657,14 @@ static Instruction *ProcessUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth))
return 0;
// This is only really a signed overflow check if the inputs have been
// sign-extended; check for that condition. For example, if CI2 is 2^31 and
// the operands of the add are 64 bits wide, we need at least 33 sign bits.
unsigned NeededSignBits = CI1->getBitWidth() - NewWidth + 1;
if (IC.ComputeNumSignBits(A) < NeededSignBits ||
IC.ComputeNumSignBits(B) < NeededSignBits)
return 0;
// In order to replace the original add with a narrower
// llvm.sadd.with.overflow, the only uses allowed are the add-with-constant
// and truncates that discard the high bits of the add. Verify that this is