[llvm] Reland "[Transforms] LoopIdiomRecognize recognize strlen and wcslen (#108985)" (PR #131412)

[Henry Jiang via llvm-commits]

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@@ -1494,7 +1512,17 @@ bool LoopIdiomRecognize::runOnNoncountableLoop() {
 
   return recognizePopcount() || recognizeAndInsertFFS() ||
          recognizeShiftUntilBitTest() || recognizeShiftUntilZero() ||
-         recognizeShiftUntilLessThan();
+         recognizeShiftUntilLessThan() || recognizeAndInsertStrLen();
+}
+
+/// Check if a Value is either a nullptr or a constant int zero
+static bool isZeroConstant(const Value *Val) {
+  if (isa<ConstantPointerNull>(Val))
+    return true;
+  const ConstantInt *CmpZero = dyn_cast<ConstantInt>(Val);
+  if (!CmpZero || !CmpZero->isZero())
+    return false;
+  return true;
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mustartt wrote:

Thank you for taking. You are right, it's no longer needed. We used to use this to condition the loop preheader on a `nullptr` comparison for the base of the string. I will clean this up

https://github.com/llvm/llvm-project/pull/131412