simplify-libcalls: fold strstr(a, b) == a -> strncmp(a, b, strlen(b)) == 0
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106047 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 7414be7..f562a1b 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -92,6 +92,20 @@
return true;
}
+/// IsOnlyUsedInEqualityComparison - Return true if it is only used in equality
+/// comparisons with With.
+static bool IsOnlyUsedInEqualityComparison(Value *V, Value *With) {
+ for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
+ UI != E; ++UI) {
+ if (ICmpInst *IC = dyn_cast<ICmpInst>(*UI))
+ if (IC->isEquality() && IC->getOperand(1) == With)
+ continue;
+ // Unknown instruction.
+ return false;
+ }
+ return true;
+}
+
//===----------------------------------------------------------------------===//
// String and Memory LibCall Optimizations
//===----------------------------------------------------------------------===//
@@ -503,6 +517,23 @@
if (CI->getOperand(1) == CI->getOperand(2))
return B.CreateBitCast(CI->getOperand(1), CI->getType());
+ // fold strstr(a, b) == a -> strncmp(a, b, strlen(b)) == 0
+ if (TD && IsOnlyUsedInEqualityComparison(CI, CI->getOperand(1))) {
+ Value *StrLen = EmitStrLen(CI->getOperand(2), B, TD);
+ Value *StrNCmp = EmitStrNCmp(CI->getOperand(1), CI->getOperand(2),
+ StrLen, B, TD);
+ for (Value::use_iterator UI = CI->use_begin(), UE = CI->use_end();
+ UI != UE; ) {
+ ICmpInst *Old = cast<ICmpInst>(UI++);
+ Value *Cmp = B.CreateICmp(Old->getPredicate(), StrNCmp,
+ ConstantInt::getNullValue(StrNCmp->getType()),
+ "cmp");
+ Old->replaceAllUsesWith(Cmp);
+ Old->eraseFromParent();
+ }
+ return CI;
+ }
+
// See if either input string is a constant string.
std::string SearchStr, ToFindStr;
bool HasStr1 = GetConstantStringInfo(CI->getOperand(1), SearchStr);