[Transforms] LoopIdiomRecognize recognize strlen and wcslen (#108985)

This PR continues the effort made in
https://discourse.llvm.org/t/rfc-strlen-loop-idiom-recognition-folding/55848
and https://reviews.llvm.org/D83392 and https://reviews.llvm.org/D88460
to extend `LoopIdiomRecognize` to find and replace loops of the form
```c
base = str;
while (*str)
  ++str;
```
and transforming the `strlen` loop idiom into the appropriate `strlen`
and `wcslen` library call which will give a small performance boost if
replaced.
```c
str = base + strlen(base)
len = str - base
```

---------

Co-authored-by: Michael Kruse <github@meinersbur.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
index 2301be6..24eefc9 100644
--- a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp
@@ -1582,6 +1582,15 @@ Value *llvm::emitStrLen(Value *Ptr, IRBuilderBase &B, const DataLayout &DL,
   return emitLibCall(LibFunc_strlen, SizeTTy, CharPtrTy, Ptr, B, TLI);
 }
 
+Value *llvm::emitWcsLen(Value *Ptr, IRBuilderBase &B, const DataLayout &DL,
+                        const TargetLibraryInfo *TLI) {
+  assert(Ptr && Ptr->getType()->isPointerTy() &&
+         "Argument to wcslen intrinsic must be a pointer.");
+  Type *PtrTy = B.getPtrTy();
+  Type *SizeTTy = getSizeTTy(B, TLI);
+  return emitLibCall(LibFunc_wcslen, SizeTTy, PtrTy, Ptr, B, TLI);
+}
+
 Value *llvm::emitStrDup(Value *Ptr, IRBuilderBase &B,
                         const TargetLibraryInfo *TLI) {
   Type *CharPtrTy = B.getPtrTy();