Summary:
This is a revised version of D13974, and the following quoted summary are from D13974
"This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can therefore rewrite the exit value with
its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch."
D13974 was committed but failed one lnt test. The bug was that we only checked the condition from loop exit's incoming block was a loop invariant. But there could be another condition from loop header to that incoming block not being a loop invariant. This would produce miscompiled code.
This patch fixes the issue by checking if the incoming block is loop header, and if not, don't perform the rewrite. The could be further improved by recursively checking all conditions leading to loop exit block, but I'd like to check in this simple version first and improve it with future patches.
Reviewers: sanjoy
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D16570
llvm-svn: 258912
Commit 251839 triggers miscompiles on some bots:
http://lab.llvm.org:8011/builders/perf-x86_64-penryn-O3-polly-fast/builds/13723
(The commit is listed in 13722, but due to an existing failure introduced in
13721 and reverted in 13723 the failure is only visible in 13723)
To verify r251839 is indeed the only change that triggered the buildbot failures
and to ensure the buildbots remain green while investigating I temporarily
revert this commit. At the current state it is unclear if this commit introduced
some miscompile or if it only exposed code to Polly that is subsequently
miscompiled by Polly.
llvm-svn: 251901
Summary:
This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can therefore rewrite the exit value with
its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch.
Reviewers: sanjoy
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D13974
llvm-svn: 251839
Summary:
This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can therefore rewrite the exit value with
its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch.
Reviewers: sanjoy
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D13974
llvm-svn: 251492
Chen Li