[llvm] [InstCombine] Simplify demanded bits of blendv mask operands (PR #173723)

[Simon Pilgrim via llvm-commits]

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@@ -2890,21 +2889,25 @@ X86TTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
           getNegativeIsTrueBoolVec(ConstantMask, IC.getDataLayout());
       return SelectInst::Create(NewSelector, Op1, Op0, "blendv");
     }
+    unsigned BitWidth = Mask->getType()->getScalarSizeInBits();
+    KnownBits Known(BitWidth);
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RKSimon wrote:

Move the KnownBits inside the `if (Mask->getType()->isIntOrIntVectorTy())` block to reduce scope (it might not be valid later on).

https://github.com/llvm/llvm-project/pull/173723