[PATCH] D98335: [AVR] Refactor 8-bit & 16-bit shifts

[Ben Shi via Phabricator via llvm-commits]

benshi001 added a comment.

As shown in test case https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/AVR/shift.ll,

this patch generates optimized code for most cases as avr-gcc does (though there are slight differences in instrution sequence).

TODO:

1. futher optimization for 8-bit `ashr x, 6`
2. remove the redundant `lsl <lower byte>` in 16-bit shl when shiftAmount>8;
3. remove the redundant `lsr <higher byte>` in 16-bit lshr when shiftAmount>8;
4. remove the redundant `asr <higher byte>` in 16-bit ashr when shiftAmount>8;


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  https://reviews.llvm.org/D98335/new/

https://reviews.llvm.org/D98335