[AggressiveInstCombine] Fold strcmp for short string literals

Fold strcmp() against 1-char string literals.

This designates AggressiveInstCombine as the pass for libcalls
simplifications that may need to change the control flow graph.

Fixes https://github.com/llvm/llvm-project/issues/58003.

Differential Revision: https://reviews.llvm.org/D154725

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 4be171e..8940c2c 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -261,6 +261,13 @@ bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
   return KnownBits::haveNoCommonBitsSet(LHSKnown, RHSKnown);
 }
 
+bool llvm::isOnlyUsedInZeroComparison(const Instruction *I) {
+  return !I->user_empty() && all_of(I->users(), [](const User *U) {
+    ICmpInst::Predicate P;
+    return match(U, m_ICmp(P, m_Value(), m_Zero()));
+  });
+}
+
 bool llvm::isOnlyUsedInZeroEqualityComparison(const Instruction *I) {
   return !I->user_empty() && all_of(I->users(), [](const User *U) {
     ICmpInst::Predicate P;