[llvm] Calculate KnownBits from Metadata correctly for vector loads (PR #128908)

[via llvm-commits]

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@@ -4004,22 +4004,25 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
         }
       }
     } else if (Op.getResNo() == 0) {
-      KnownBits Known0(!LD->getMemoryVT().isScalableVT()
-                           ? LD->getMemoryVT().getFixedSizeInBits()
-                           : BitWidth);
+      unsigned MemorySize = !LD->getMemoryVT().isScalableVT()
+                                ? LD->getMemoryVT().getFixedSizeInBits()
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LU-JOHN wrote:

> This is using the full vector bitwidth. The range is in terms of the scalar element size

The KnownBits passed to computeKnownBitsFromRangeMetadata on line 4022 is sized to the range metadata size.  Previously it was incorrectly sized to MemorySize.

https://github.com/llvm/llvm-project/pull/128908