[llvm-bugs] [Bug 24500] New: RA breaks invariance of generated code

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24500

            Bug ID: 24500
           Summary: RA breaks invariance of generated code
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: anton.nadolskiy at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 14746
  --> https://llvm.org/bugs/attachment.cgi?id=14746&action=edit
Source and includes. Also two .s files that show difference

LLVM produces different code from run to run for given source. After examining
dump file I found that differences begin after Virtual Register Rewriter pass.
And it seems like problem appears only with -mregparm=3.

Example I took is from Spec2000 suite. It's 177.mesa/copypix.c  I couldn't
reduce test. I've tried to cut all but one function (where differences appear -
see .s files), but generated code seemed to be always the same.

Options I used: 
clang -Os -c -m32 -mregparm=3 -march=pentium -Wno-return-type -Xclang
-msoft-float -mstack-alignment=4 copypix.c

But as I said only -mregparm=3 matters.

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