[SimplifyLibCalls] Fix memchr expansion for constant strings.

The C standard says "The memchr function locates the first
occurrence of c (converted to an unsigned char)[...]".  The expansion
was missing the conversion to unsigned char.

Fixes https://bugs.llvm.org/show_bug.cgi?id=39041 .

Differential Revision: https://reviews.llvm.org/D55947

llvm-svn: 350775

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index a50575b0256..1bb26caa2af 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -798,8 +798,11 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) {
       Bitfield.setBit((unsigned char)C);
     Value *BitfieldC = B.getInt(Bitfield);
 
-    // First check that the bit field access is within bounds.
+    // Adjust width of "C" to the bitfield width, then mask off the high bits.
     Value *C = B.CreateZExtOrTrunc(CI->getArgOperand(1), BitfieldC->getType());
+    C = B.CreateAnd(C, B.getIntN(Width, 0xFF));
+
+    // First check that the bit field access is within bounds.
     Value *Bounds = B.CreateICmp(ICmpInst::ICMP_ULT, C, B.getIntN(Width, Width),
                                  "memchr.bounds");