[PATCH] D150107: [X86] Remove patterns for shift/rotate with immediate 1 and update side effect

[Kan Shengchen via Phabricator via llvm-commits]

skan added a comment.

In D150107#4326328 <https://reviews.llvm.org/D150107#4326328>, @RKSimon wrote:

> What is the motivation here?

It's first suggested by craig in D150068 <https://reviews.llvm.org/D150068>. I think there are at least three pros

1. This can reduce the patterns during ISEL, as a result, reducing the bytes in X86GenDAGISel.inc
2. The patterns for shift/rotate with immediate 1 look quite similar to shift/rotate with immediate 8. So this can be seen as eliminating "duplicate" code.
3. Delay the optimization from imm8 to imm1, so that the previous optimization passes do not need to handle the version of imm1


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