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Question on register renaming in rtl loop unroll pass
- From: "Bin.Cheng" <amker dot cheng at gmail dot com>
- To: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Fri, 28 Jun 2013 17:52:07 +0800
- Subject: Question on register renaming in rtl loop unroll pass
Hi, I have a question about register renaming in rtl loop unroll.
For an example loop:
.L1:
[r162] <- x
r162 <- r162 + 4
...
b .L1
After unrolling:
.L1:
[r162] <- x
r197 <- r162 + 4
r162 <- r197
...
[r162] <- y
r162 <- r197 + 4
...
b .L1
Why not:
.L1:
[r162] <- x
r162 <- r162 + 4
...
[r162] <- y
r162 <- r162 + 4
...
b .L1
Thus less copy instructions and can take advantage of auto-increment.
Any ideas?
Thanks.
bin