[Bug middle-end/51182] [ipa-iterations] running multiple passes of early IPA on a file produces difference code when it shouldn't

[matt at use dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51182

--- Comment #1 from Matt Hargett <matt at use dot net> 2011-11-16 23:09:22 UTC ---
I see the same seeming no-op register and instruction twiddles with inflate.c
from zlib, as well. Adding more iterations has a kind of ping-pong effect where
it goes between the two different versions.


diff inflate.o.-O3.ipa-iterations2.dump inflate.o.-O3.ipa-iterations3.dump2c2
< inflate.o.-O3.ipa-iterations2:     file format elf64-x86-64
---
> inflate.o.-O3.ipa-iterations3:     file format elf64-x86-64
897,898c897,898
<      d22:    31 db                    xor    %ebx,%ebx
<      d24:    45 31 d2                 xor    %r10d,%r10d
---
>      d22:	45 31 d2             	xor    %r10d,%r10d
>      d25:	31 db                	xor    %ebx,%ebx
1731c1731
<     19a9:    44 39 c7                 cmp    %r8d,%edi
---
>     19a9:	41 39 f8             	cmp    %edi,%r8d
2192,2193c2192,2193
<     20e0:    45 31 d2                 xor    %r10d,%r10d
<     20e3:    31 db                    xor    %ebx,%ebx
---
>     20e0:	31 db                	xor    %ebx,%ebx
>     20e2:	45 31 d2             	xor    %r10d,%r10d