SimplifyLibCalls: Add basic optimization of memchr calls.
This is just memchr(x, y, 0) -> nullptr and constant folding.
llvm-svn: 232896
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index a30514e..0d0b77a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -745,6 +745,44 @@
return nullptr;
}
+Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) {
+ Function *Callee = CI->getCalledFunction();
+ FunctionType *FT = Callee->getFunctionType();
+ if (FT->getNumParams() != 3 || !FT->getParamType(0)->isPointerTy() ||
+ !FT->getParamType(1)->isIntegerTy(32) ||
+ !FT->getParamType(2)->isIntegerTy() ||
+ !FT->getReturnType()->isPointerTy())
+ return nullptr;
+
+ Value *SrcStr = CI->getArgOperand(0);
+ ConstantInt *CharC = dyn_cast<ConstantInt>(CI->getArgOperand(1));
+ ConstantInt *LenC = dyn_cast<ConstantInt>(CI->getArgOperand(2));
+
+ // memchr(x, y, 0) -> null
+ if (LenC && LenC->isNullValue())
+ return Constant::getNullValue(CI->getType());
+
+ // Check if all arguments are constants. If so, we can constant fold.
+ StringRef Str;
+ if (!CharC || !LenC ||
+ !getConstantStringInfo(SrcStr, Str, /*Offset=*/0,
+ /*TrimAtNul=*/false))
+ return nullptr;
+
+ // Truncate the string to LenC. If Str is smaller than LenC we will still only
+ // scan the string, as reading past the end of it is undefined and we can just
+ // return null if we don't find the char.
+ Str = Str.substr(0, LenC->getZExtValue());
+
+ // Compute the offset.
+ size_t I = Str.find(CharC->getSExtValue() & 0xFF);
+ if (I == StringRef::npos) // Didn't find the char. memchr returns null.
+ return Constant::getNullValue(CI->getType());
+
+ // memchr(s+n,c,l) -> gep(s+n+i,c)
+ return B.CreateGEP(SrcStr, B.getInt64(I), "memchr");
+}
+
Value *LibCallSimplifier::optimizeMemCmp(CallInst *CI, IRBuilder<> &B) {
Function *Callee = CI->getCalledFunction();
FunctionType *FT = Callee->getFunctionType();
@@ -1852,6 +1890,8 @@
return optimizeStrCSpn(CI, Builder);
case LibFunc::strstr:
return optimizeStrStr(CI, Builder);
+ case LibFunc::memchr:
+ return optimizeMemChr(CI, Builder);
case LibFunc::memcmp:
return optimizeMemCmp(CI, Builder);
case LibFunc::memcpy: