[llvm] Ensure KnownBits passed when calculating from range md has right size (PR #132985)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: None (LU-JOHN)

<details>
<summary>Changes</summary>

KnownBits passed to computeKnownBitsFromRangeMetadata must have the same bit width as the range metadata bit width.  Otherwise the calculated results will be incorrect.

---
Full diff: https://github.com/llvm/llvm-project/pull/132985.diff


1 Files Affected:

- (modified) llvm/lib/Analysis/ValueTracking.cpp (+2) 


``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 880781742fae0..4e3d5d8f12cbc 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -433,6 +433,8 @@ void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
     // The first CommonPrefixBits of all values in Range are equal.
     unsigned CommonPrefixBits =
         (Range.getUnsignedMax() ^ Range.getUnsignedMin()).countl_zero();
+    // BitWidth must equal the Ranges BitWidth for the correct number of high bits to be set.
+    assert(BitWidth == Lower->getBitWidth() );
     APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits);
     APInt UnsignedMax = Range.getUnsignedMax().zextOrTrunc(BitWidth);
     Known.One &= UnsignedMax & Mask;

``````````

</details>


https://github.com/llvm/llvm-project/pull/132985