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

[via llvm-commits]

https://github.com/LU-JOHN created https://github.com/llvm/llvm-project/pull/132985

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

>From 0b5ed292c15ca73144660f0912f0c955abd639e7 Mon Sep 17 00:00:00 2001
From: John Lu <John.Lu at amd.com>
Date: Tue, 25 Mar 2025 14:59:23 -0500
Subject: [PATCH] Ensure KnownBits passed to computeKnownBitsFromRangeMetadata
 has correct size

Signed-off-by: John Lu <John.Lu at amd.com>
---
 llvm/lib/Analysis/ValueTracking.cpp | 2 ++
 1 file changed, 2 insertions(+)

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;