Konstantin Schwarz 64bef13f08 [GlobalISel] Look through truncs and extends in narrowScalarShift ...

If a G_SHL is fed by a G_CONSTANT, the lower and upper bits of the source can be
shifted individually by the constant shift amount.

However in case the shift amount came from a G_TRUNC(G_CONSTANT), the generic shift legalization
code was used, producing intermediate shifts that are potentially illegal on some targets.

This change teaches narrowScalarShift to look through G_TRUNCs and G_*EXTs.

Reviewed By: paquette

Differential Revision: https://reviews.llvm.org/D89100

2021-08-10 13:49:22 +02:00

141 KiB

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