[PATCH] D22011: [SystemZ] Generate fewer instructions for (sub <constant>, x)

[Assem Bsoul via llvm-commits]

assem added a comment.

Thanks for the comment, Ulrich!

Compared to the old version the new version uses less instructions and only one register. Compared to your suggested change, the new version uses 1 less register. I can run some performance tests (micro benchmarks) to test the performance impact of the new change, but I thought the advantage is clear.

I am not sure what you do mean by the "longer" dependency chain. If I understand correctly, the old version has longer dependency chain and your suggested change has the same dependency chain length (sgrk requires result from lghi) as the new version in the patch. If I misunderstood, can you please clarify?

Thanks


http://reviews.llvm.org/D22011