[llvm-bugs] [Bug 26450] New: ARM code runs 2x slower compared to gcc

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Feb 3 04:42:49 PST 2016


            Bug ID: 26450
           Summary: ARM code runs 2x slower compared to gcc
           Product: clang
           Version: 3.7
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: tulipawn at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 15810
  --> https://llvm.org/bugs/attachment.cgi?id=15810&action=edit
C source sample

I've recently discovered the sad fact code produced by LLVM on ARM was nowhere
near the speed of gcc:


The same C code (as well as rust code) compiled with -O3 yields identical
performance on x86_64 between gcc/clang/rustc whereas on armv7:

gcc -             1.5s
clang/rustc -     3.4s (3.2s using --ffast-math)

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