[PATCH] D39536: [PowerPC] Eliminate redundant register copys after register allocation

[Hiroshi Inoue via Phabricator via llvm-commits]

inouehrs added a comment.

@gberry Thank you for the comment!
Many redundant register copies (e.g. about 2/3 of the intra-BB redundancies) are generated by optimizers executed after COPYs are expanded to real instructions. To catch them, this optimization is run just before code emission.
So, MachineCopyPropagation, which is executed just after register allocation, may not  be able to catch these opportunities.
(For example, when I run this pass just after pseudo instruction expansion, optimizations happen 7780 times during the bootstrap while they happen 10255 times if the pass is executed at the very last of the compilation.)


https://reviews.llvm.org/D39536