https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107115
Alexander Monakov <amonakov at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |amonakov at gcc dot gnu.org,
| |jakub at gcc dot gnu.org
--- Comment #6 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
Cc'ing Jakub for the problematic i386.md peephole that loses alias set info.
As Andrew mentioned in comment #2, the next stop is combine, which sees
(set (mem:DI (plus:DI (mult:DI (sign_extend:DI (reg:SI 101))
(const_int 8 [0x8]))
(reg/v/f:DI 90 [ p4 ])) [1 MEM[(long int *)_11]+0 S8 A64])
(mem:DI (plus:DI (mult:DI (sign_extend:DI (reg:SI 101))
(const_int 8 [0x8]))
(reg/v/f:DI 90 [ p4 ])) [2 *_11+0 S8 A64]))
as a no-op move and removes it (but note differing alias sets in the MEMs).
And with -fdisable-rtl-combine it is then broken by peephole2 of all things:
;; Attempt to optimize away memory stores of values the memory already
;; has. See PR79593.
(define_peephole2
[(set (match_operand 0 "register_operand")
(match_operand 1 "memory_operand"))
(set (match_operand 2 "memory_operand") (match_dup 0))]
"!MEM_VOLATILE_P (operands[1])
&& !MEM_VOLATILE_P (operands[2])
&& rtx_equal_p (operands[1], operands[2])
&& !reg_overlap_mentioned_p (operands[0], operands[2])"
[(set (match_dup 0) (match_dup 1))])
