[Bug target/50788] [4.7 Regression] ICE: in merge_overlapping_regs, at regrename.c:318 with -mavx -fpeel-loops -fstack-protector-all and __builtin_ia32_maskloadpd256

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50788

--- Comment #7 from Uros Bizjak <ubizjak at gmail dot com> 2011-10-23 11:45:32 UTC ---
(In reply to comment #6)
> > It is OK for expanders to have match_dup. We just don't want to have
> > post-reload passes to trip on double-output to the same register.
> 
> No disagreement.  I just wanted to state the argument for the + approach, but
> the manual clearly points to the match_operand approach here instead.

cprop_hardreg of 4-6 branch is even more confused:

(insn 30 5 10 2 (set (reg:V4DF 22 xmm1 [63])
        (const_vector:V4DF [
                (const_double:DF 0.0 [0x0.0p+0])
                (const_double:DF 0.0 [0x0.0p+0])
                (const_double:DF 0.0 [0x0.0p+0])
                (const_double:DF 0.0 [0x0.0p+0])
            ])) pr50788.c:6 1120 {*avx_movv4df_internal}
     (expr_list:REG_EQUAL (const_vector:V4DF [
                (const_double:DF 0.0 [0x0.0p+0])
                (const_double:DF 0.0 [0x0.0p+0])
                (const_double:DF 0.0 [0x0.0p+0])
                (const_double:DF 0.0 [0x0.0p+0])
            ])
        (nil)))

(insn 10 30 16 2 (set (reg:V4DF 22 xmm1 [63])
        (unspec:V4DF [
                (mem:V4DF (reg/v/f:DI 5 di [orig:61 __P ] [61]) [0 S32 A8])
                (reg/v:V4DI 21 xmm0 [orig:62 __M ] [62])
                (reg:V4DF 21 xmm0 [63])
            ] UNSPEC_MASKLOAD)) pr50788.c:6 2086 {avx_maskloadpd256}
     (expr_list:REG_DEAD (reg/v:V4DI 21 xmm0 [orig:62 __M ] [62])
        (expr_list:REG_DEAD (reg/v/f:DI 5 di [orig:61 __P ] [61])
            (nil))))

See how in (insn 10) pseudo [63] gets allocated xmm1 _and_ xmm0. Following DCE
is more than happy to throw everything out of instruction stream.