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llvm-mirror/test/Transforms/LoopRotate
Andrew Trick 5d13ab6ea6 Rotate multi-exit loops even if the latch was simplified.
Test case by Michele Scandale!

Fixes PR10293: Load not hoisted out of loop with multiple exits.

There are few regressions with this patch, now tracked by
rdar:13817079, and a roughly equal number of improvements. The
regressions are almost certainly back luck because LoopRotate has very
little idea of whether rotation is profitable. Doing better requires a
more comprehensive solution.

This checkin is a quick fix that lacks generality (PR10293 has
a counter-example). But it trivially fixes the case in PR10293 without
interfering with other cases, and it does satify the criteria that
LoopRotate is a loop canonicalization pass that should avoid
heuristics and special cases.

I can think of two approaches that would probably be better in
the long run. Ultimately they may both make sense.

(1) LoopRotate should check that the current header would make a good
loop guard, and that the loop does not already has a sufficient
guard. The artifical SimplifiedLoopLatch check would be unnecessary,
and the design would be more general and canonical. Two difficulties:

- We need a strong guarantee that we won't endlessly rotate, so the
  analysis would need to be precise in order to avoid the
  SimplifiedLoopLatch precondition.

- Analysis like this are usually based on SCEV, which we don't want to
  rely on.

(2) Rotate on-demand in late loop passes. This could even be done by
shoving the loop back on the queue after the optimization that needs
it. This could work well when we find LICM opportunities in
multi-branch loops. This requires some work, and it doesn't really
solve the problem of SCEV wanting a loop guard before the analysis.

llvm-svn: 181230
2013-05-06 17:58:18 +00:00
..
2009-01-25-SingleEntryPhi.ll
alloca.ll
basic.ll Tests: rewrite 'opt ... %s' to 'opt ... < %s' so that opt does not emit a ModuleID 2012-12-30 01:28:40 +00:00
crash.ll Tests: rewrite 'opt ... %s' to 'opt ... < %s' so that opt does not emit a ModuleID 2012-12-30 02:33:22 +00:00
dbgvalue.ll Tests: rewrite 'opt ... %s' to 'opt ... < %s' so that opt does not emit a ModuleID 2012-12-30 01:28:40 +00:00
indirectbr.ll
lit.local.cfg Replace all instances of dg.exp file with lit.local.cfg, since all tests are run with LIT now and now Dejagnu. dg.exp is no longer needed. 2012-02-16 06:28:33 +00:00
multiple-exits.ll LoopRotation: Make the brute force DomTree update more brute force. 2012-09-02 11:57:22 +00:00
phi-duplicate.ll Tests: rewrite 'opt ... %s' to 'opt ... < %s' so that opt does not emit a ModuleID 2012-12-30 01:28:40 +00:00
PhiRename-1.ll llvm/test/Transforms/LoopRotate/PhiRename-1.ll: FileCheck-ize. It fixes PR13301. 2012-07-17 15:43:17 +00:00
PhiSelfRefernce-1.ll
pr2639.ll
preserve-scev.ll
simplifylatch.ll Rotate multi-exit loops even if the latch was simplified. 2013-05-06 17:58:18 +00:00