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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113630] [11/12/13/14 Regression]
 -fno-strict-aliasing introduces out-of-bounds memory access
Date: Mon, 29 Jan 2024 08:04:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113630

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> Note LLVM produces decent code here by only using one load:
> ```
>         xor     eax, eax
>         test    esi, esi
>         sete    al
>         mov     eax, dword ptr [rdi + 4*rax]
> ```
>=20
> Maybe GCC could do the same ...

IIRC there's duplicate bugs about this - phiprop does kind-of the reverse.
The sink pass can now sink two exactly same stores but doesn't try sinking
a "compatible" store by introducing a PHI for the address.

              /* ??? We could handle differing SSA uses in the LHS by inser=
ting
                 PHIs for them.  */
              else if (! operand_equal_p (gimple_assign_lhs (first_store),
                                          gimple_assign_lhs (def), 0)
                       || (gimple_clobber_p (first_store)
                           !=3D gimple_clobber_p (def)))=