[LLVMbugs] [Bug 21296] New: Performance regression on ARM within (219545, 219569]

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu Oct 16 02:58:04 PDT 2014


            Bug ID: 21296
           Summary: Performance regression on ARM within (219545, 219569]
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: renato.golin at linaro.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Our benchmark buildbot detected a regression on ARM:


According to Hal:

Based on the commit logs, it does seem like the best candidates are:
  r219566, r219567, r219568 - InstCombine bug fixes re: no-wrap flags
  r219550, r219562 - Fixes to trip-count computations in the

and given the magnitude of the change, I think that the trip-count changes are
more likely.

Since those were bug fixes, we should proceed with caution and make sure there
isn't a fix on top of those patches before considering anything more radical.

It may very well be that the ARM back-end is not dealing with some new patterns
correctly, or that the transformation has generated unoptimal sequences.

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