Craig Topper a105d3024e [X86] Fold (shift undef, X)->0 for vector shifts by immediate. ...

We could previously do this by accident through the later
call to getTargetConstantBitsFromNode I think, but that only worked
if N0 had a single use. This patch makes it explicit for undef and
doesn't have a use count check.

I think this is needed to move the (shl X, 1)->(add X, X)
fold to isel for PR50468. We need to be sure X won't be IMPLICIT_DEF
which might prevent the same vreg from being used for both operands.

Differential Revision: https://reviews.llvm.org/D103192

2021-05-27 09:31:47 -07:00

7.3 KiB

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