tree e586843214a6ead8ed274250e1c8705a034fa440
parent 53422e8b4f65a6736896311b10ad8a22fbc9e372
author Simon Pilgrim <llvm-dev@redking.me.uk> 1593787866 +0100
committer Simon Pilgrim <llvm-dev@redking.me.uk> 1593788530 +0100

[InstCombine] canEvaluateTruncated - use KnownBits to check for inrange shift amounts

Currently canEvaluateTruncated can only attempt to truncate shifts if they are scalar/uniform constant amounts that are in range.

This patch replaces the constant extraction code with KnownBits handling, using the KnownBits::getMaxValue to check that the amounts are inrange.

This enables support for nonuniform constant cases, and also variable shift amounts that have been masked somehow. Annoyingly, this still won't work for vectors with (demanded) undefs as KnownBits returns nothing in those cases, but its a definite improvement on what we currently have.

Differential Revision: https://reviews.llvm.org/D83127