[PATCH] D22011: [SystemZ] Generate fewer instructions for (sub <constant>, x)
Ulrich Weigand via llvm-commits
llvm-commits at lists.llvm.org
Wed Jul 6 07:17:07 PDT 2016
uweigand added a comment.
So I see that we get less instructions in this particular case. However, I'm wondering whether execution is also *faster*, given that the new code seems to create longer dependency chains. Normally I'd like to compare benchmark runs before making a change like that ...
Also, I'm wondering why we can't have the best of both worlds: just two instructions *and* the shorter dependency chain, by creating instead something like:
lghi %r0, 63
sgrk %r2, %r0, %r2
(assuming we're on z196 and higher. But then I don't think z10 is a big concern these days anyway.)
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