[llvm-bugs] [Bug 26106] New: Loop Vectorizer on ARM - why is the relative speedup so much worse?

via llvm-bugs llvm-bugs at lists.llvm.org
Sun Jan 10 13:09:03 PST 2016


            Bug ID: 26106
           Summary: Loop Vectorizer on ARM - why is the relative speedup
                    so much worse?
           Product: libraries
           Version: 3.6
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: tulipawn at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 15600
  --> https://llvm.org/bugs/attachment.cgi?id=15600&action=edit
armv7 LLVM-IR output


It's my first issue here (I only use llvm via rust) so I might be mistaken in
my understanding but here's the problem. The code snippet from this rust issue:


is being successfully optimized on x86_64 and posts a 20x speedup using SSE2
whereas on ARM it's a meagre 3x speedup using NEON.

The relative difference seems a little high - is there a problem somewhere on

I'm attaching armv7 LLVM-IR in case there is.


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