[llvm] [ValueTracking] Use `ConstantRange::toKnownBits` when computing from Range Metadata; NFC (PR #85574)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: None (goldsteinn)

<details>
<summary>Changes</summary>

Just replaces some bespoke logic with a better tested API.


---
Full diff: https://github.com/llvm/llvm-project/pull/85574.diff


1 Files Affected:

- (modified) llvm/lib/Analysis/ValueTracking.cpp (+1-11) 


``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index edbeede910d7f7..7f25f358aa8b30 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -423,23 +423,13 @@ void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
   unsigned NumRanges = Ranges.getNumOperands() / 2;
   assert(NumRanges >= 1);
 
-  Known.Zero.setAllBits();
-  Known.One.setAllBits();
-
   for (unsigned i = 0; i < NumRanges; ++i) {
     ConstantInt *Lower =
         mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0));
     ConstantInt *Upper =
         mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1));
     ConstantRange Range(Lower->getValue(), Upper->getValue());
-
-    // The first CommonPrefixBits of all values in Range are equal.
-    unsigned CommonPrefixBits =
-        (Range.getUnsignedMax() ^ Range.getUnsignedMin()).countl_zero();
-    APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits);
-    APInt UnsignedMax = Range.getUnsignedMax().zextOrTrunc(BitWidth);
-    Known.One &= UnsignedMax & Mask;
-    Known.Zero &= ~UnsignedMax & Mask;
+    Known = Known.unionWith(Range.toKnownBits());
   }
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/85574