[Bug rtl-optimization/67145] [6 Regression] associativity from pseudo-reg ordering

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67145

--- Comment #7 from Alan Modra <amodra at gmail dot com> ---
See https://gcc.gnu.org/ml/gcc-patches/2015-05/msg02055.html

The patch proposed here will again "simplify"

(plus:DI (plus:DI (reg:DI 165 [ val+8 ])
        (reg:DI 169 [+8 ]))
    (reg:DI 76 ca))

to this

(plus:DI (plus:DI (reg:DI 76 ca)
        (reg:DI 165 [ val+8 ]))
    (reg:DI 169 [+8 ]))

breaking the match of rs6000.md adddi3_carry_in_internal.

Please do *not* apply this patch as it regresses powerpc64, and please read
comment #1 for why the patch is the wrong place to change associativity.