[llvm] [ValueTracking] Take into account whether zero is poison when computing CR for `ct{t,l}z` (PR #122548)

[via llvm-commits]

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@@ -9898,13 +9898,20 @@ static void setLimitsForBinOp(const BinaryOperator &BO, APInt &Lower,
   }
 }
 
-static ConstantRange getRangeForIntrinsic(const IntrinsicInst &II) {
+static ConstantRange getRangeForIntrinsic(const IntrinsicInst &II,
+                                          bool UseInstrInfo) {
   unsigned Width = II.getType()->getScalarSizeInBits();
   const APInt *C;
   switch (II.getIntrinsicID()) {
-  case Intrinsic::ctpop:
   case Intrinsic::ctlz:
-  case Intrinsic::cttz:
+  case Intrinsic::cttz: {
+    APInt Upper = APInt(Width, Width);
+    if (!UseInstrInfo || !match(II.getArgOperand(1), m_One()))
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goldsteinn wrote:

Think attr would make more sense, its typically how we communicate poison generating constraints.

https://github.com/llvm/llvm-project/pull/122548