[AggressiveInstCombine] Implement memchr inlining optimization

This patch implements an optimization to inline small memchr calls into a sequence of loads and comparisons when the length is below a threshold. This allows better optimization of small string searches.

The implementation: Adds support for inlining memchr calls with constant length, introduces a memchr-inline-threshold parameter (default: 6), and adds test coverage for small memchr operations.

Author: natedal

AggressiveInstCombine.cpp

@@ -0,0 +1,43 @@
+static bool foldMemChr(CallInst *Call, DomTreeUpdater *DTU,
+                       const DataLayout &DL) {
+  Value *Ptr = Call->getArgOperand(0);
+  Value *Val = Call->getArgOperand(1);
+  Value *Len = Call->getArgOperand(2);
+
+  // If length is not a constant, we can't do the optimization
+  auto *LenC = dyn_cast<ConstantInt>(Len);
+  if (!LenC)
+    return false;
+
+  uint64_t Length = LenC->getZExtValue();
+
+  // Check if this is a small memchr we should inline
+  if (Length <= MemChrInlineThreshold) {
+    IRBuilder<> IRB(Call);
+
+    // Truncate the search value to i8
+    Value *ByteVal = IRB.CreateTrunc(Val, IRB.getInt8Ty());
+
+    // Initialize result to null
+    Value *Result = ConstantPointerNull::get(cast<PointerType>(Call->getType()));
+
+    // For each byte up to Length
+    for (unsigned i = 0; i < Length; i++) {
+      Value *CurPtr = i == 0 ? Ptr : 
+                     IRB.CreateGEP(IRB.getInt8Ty(), Ptr, 
+                                 ConstantInt::get(DL.getIndexType(Call->getType()), i));
+      Value *CurByte = IRB.CreateLoad(IRB.getInt8Ty(), CurPtr);
+      Value *CmpRes = IRB.CreateICmpEQ(CurByte, ByteVal);
+      Result = IRB.CreateSelect(CmpRes, CurPtr, Result);
+    }
+
+    // Replace the call with our expanded version
+    Call->replaceAllUsesWith(Result);
+    Call->eraseFromParent();
+    return true;
+  }
+
+  return false;
+}
+
+// ... rest of the file unchanged ...