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

[Mikhail Gudim 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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mgudim wrote:

@goldsteinn Maybe I didn't understand what you mean. But I tried the following test without my patch:

```
define i1 @foo(i32 %x)  {
entry:
  %cmp0_ = icmp ule i32 %x, 10
  %select_ = select i1 %cmp0_, i32 %x, i32 10
  %cmp1_ = icmp ule i32 %select_, 10
  ret i1 %cmp1_
}
```

This simplifies to:

```
define i1 @foo(i32 %x) {
entry:
  ret i1 true
}
```

I put a print statement right after a call to `setLimitsForSelectPattern(*SI, Lower, Upper, IIQ)`, the return range is `[0, 11)`.
Can you please demonstrate what's missing with another test case?

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