[llvm] [ValueTracking] Try to infer range of select from true and false values. (PR #68256)

[via llvm-commits]

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@@ -8854,11 +8854,16 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool ForSigned,
   } else if (auto *II = dyn_cast<IntrinsicInst>(V))
     CR = getRangeForIntrinsic(*II);
   else if (auto *SI = dyn_cast<SelectInst>(V)) {
+    ConstantRange CRTrue = computeConstantRange(
+        SI->getTrueValue(), ForSigned, UseInstrInfo, AC, CtxI, DT, Depth + 1);
+    ConstantRange CRFalse = computeConstantRange(
+        SI->getFalseValue(), ForSigned, UseInstrInfo, AC, CtxI, DT, Depth + 1);
+    CR = CRTrue.unionWith(CRFalse);
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goldsteinn wrote:

not quite, but the logic i'm proposing looks like it belongs better there. I'll make a patch for that.

https://github.com/llvm/llvm-project/pull/68256