Add a missing safety check to ProcessUGT_ADDCST_ADD. Fixes PR11438.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145316 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index bb1cbfa..274758c 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1657,6 +1657,14 @@
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