[Matrix] Add assert to extractVector with undef values

[thegameg]

Summary

Assert when the extracted vector is wider than the row/column.

[fhahn]

LGTM, thanks!

[Matrix] Add assert to extractVector with undef values

might be slightly clearer to say something like [Matrix] Add assert to catch extracted vectors with poison elements

llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp

343

nit: Technically it would contain poison values now right?

[thegameg]

llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp

343

Yep that's correct!

llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp

public:
     }
 
     /// Extract a vector of \p NumElts starting at index (\p I, \p J). If the
     /// matrix is column-major, the result vector is extracted from a column
     /// vector, otherwise from a row vector.
     Value *extractVector(unsigned I, unsigned J, unsigned NumElts,
                          IRBuilder<> &Builder) const {
       Value *Vec = isColumnMajor() ? getColumn(J) : getRow(I);
+      assert(cast<FixedVectorType>(Vec->getType())->getNumElements() >=
+                 NumElts &&
+             "Extracted vector will contain poison values");
       return Builder.CreateShuffleVector(
           Vec, createSequentialMask(isColumnMajor() ? I : J, NumElts, 0),
           "block");
     }
   };
 
   struct ShapeInfo {
     unsigned NumRows;