[LLVMbugs] [Bug 23594] New: Inconsistent order of x86 instruction prefixes with -via-file-asm

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23594

            Bug ID: 23594
           Summary: Inconsistent order of x86 instruction prefixes with
                    -via-file-asm
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: MC
          Assignee: unassignedbugs at nondot.org
          Reporter: russell_gallop at sn.scee.net
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The order of x86 instruction prefixes is inconsistent if an asm file is written
out. Tested with revision 237107.

$ cat test.cpp
bool test() {
    unsigned short val;
    return __sync_bool_compare_and_swap_2(&val, 0, 0);
}

$ clang -c test.cpp && objdump -d test.o

test.o:     file format elf64-x86-64
...
   c:   66 f0 0f b1 4d fe       lock cmpxchg %cx,-0x2(%rbp)

$ clang -via-file-asm -c test.cpp && objdump -d test.o

test.o:     file format elf64-x86-64
...
   c:   f0 66 0f b1 4d fe       lock cmpxchg %cx,-0x2(%rbp)

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