https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111267
--- Comment #3 from Roger Sayle <roger at nextmovesoftware dot com> ---
This patch addresses the regression, but probably isn't the correct fix.
The issue is that the backend now has a way of representing the concatenation
of two registers (for example, TI is constructed for two DI mode registers):
(set (reg:TI 111 [ bD.2764 ])
(ior:TI (ashift:TI (zero_extend:TI (reg:DI 142))
(const_int 64 [0x40]))
(zero_extend:TI (reg:DI 141))))
But combine is unable to cleanly extract the (original) DI mode components back
out of this using SUBREGs. Currently combine gets confused and attempts to
match things like:
Trying 10 -> 74:
10: r111:TI=zero_extend(r142:DI)<<0x40|zero_extend(r141:DI)
REG_DEAD r141:DI
REG_DEAD r142:DI
74: r137:DI=r111:TI#0
Failed to match this instruction:
(parallel [
(set (reg:DI 137 [ bD.2764 ])
(reg:DI 141))
(set (reg:TI 111 [ bD.2764 ])
(ior:TI (ashift:TI (zero_extend:TI (reg:DI 142))
(const_int 64 [0x40]))
(zero_extend:TI (reg:DI 141))))
])
which contains the simplification we want, "reg:DI 137 := reg:DI 141", but
along with stuff that combine should really take care off (strip/duplicate).
I'll work on a more acceptable middle-end fix, but this patch demonstrates
progress, and can be used if a more general solution can't be found.
