[llvm] [ValueTracking] Handle intrinsics in `computeConstantRange` (PR #100870)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> for the [#95255 (comment)](https://github.com/llvm/llvm-project/issues/95255#issuecomment-2166944909) is it not enough to do a non Zero check something like this in the foldCtpop
> 
> ```
>     unsigned KnownMinPop = Known.countMinPopulation();
>     unsigned Lower =
>         KnownMinPop ? KnownMinPop
>                     : isKnownNonZero(
>                           Op0, IC.getSimplifyQuery().getWithInstruction(&II));
>     ConstantRange Range(APInt(BitWidth, Lower),
>                         APInt(BitWidth, Known.countMaxPopulation() + 1));
> ```

Are you willing to file a PR with this method? I drafted an alternative patch before submitting this PR:
```
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index f6c4b6e18093..9f04ed85e831 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -692,12 +692,17 @@ static Instruction *foldCtpop(IntrinsicInst &II, InstCombinerImpl &IC) {
                             Ty);
 
   // Add range attribute since known bits can't completely reflect what we know.
-  if (BitWidth != 1 && !II.hasRetAttr(Attribute::Range) &&
-      !II.getMetadata(LLVMContext::MD_range)) {
-    ConstantRange Range(APInt(BitWidth, Known.countMinPopulation()),
-                        APInt(BitWidth, Known.countMaxPopulation() + 1));
-    II.addRangeRetAttr(Range);
-    return ⅈ
+  if (BitWidth != 1) {
+    ConstantRange OldRange = II.getRange().value_or(ConstantRange::getNonEmpty(APInt::getZero(BitWidth),
+                                      APInt(BitWidth, BitWidth + 1)));
+    ConstantRange Range = OldRange;
+    Range = Range.intersectWith(ConstantRange(APInt(BitWidth, Known.countMinPopulation()), APInt(BitWidth, Known.countMaxPopulation() + 1)), ConstantRange::Unsigned);
+    if (Range.contains(APInt::getZero(BitWidth)) && isKnownNonZero(Op0, IC.getSimplifyQuery().getWithInstruction(&II)))
+      Range = Range.intersectWith(ConstantRange(APInt(BitWidth, 1), APInt(BitWidth, BitWidth + 1)), ConstantRange::Unsigned);
+    if (Range != OldRange) {
+      II.addRangeRetAttr(Range);
+      return ⅈ
+    }
   }
 
   return nullptr;
```

https://github.com/llvm/llvm-project/pull/100870