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From: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/107115] Wrong codegen from TBAA under stores that
 change effective type?
Date: Thu, 06 Oct 2022 15:19:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107115

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amonakov at gcc dot gnu.or=
g,
                   |                            |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))])=