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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug debug/104407] [10/11/12 Regression] '-fcompare-debug' failure
 (length) w/ -std=c++17 -O1
Date: Sun, 06 Feb 2022 08:51:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104407

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |10.4
           Keywords|                            |needs-bisection
   Last reconfirmed|                            |2022-02-06
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
      Known to fail|                            |10.3.0, 11.1.0
      Known to work|                            |10.2.0

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, the alignment with -g is 64 for the load but 128 without -g.

-g:
(insn 9 8 10 (set (reg/f:DI 83)
        (symbol_ref:DI ("a") [flags 0x2]  <var_decl 0x7f642e3a7cf0 a>))
"/app/example.cpp":4:6 -1
     (nil))

(insn 10 9 11 (set (reg:TI 84)
        (mem/c:TI (reg/f:DI 83) [1 a+0 S16 A64])) "/app/example.cpp":4:6 -1
     (nil))

vs:
(insn 6 5 7 (set (reg/f:DI 83)
        (symbol_ref:DI ("a") [flags 0x2]  <var_decl 0x7f69102a2cf0 a>))
"/app/example.cpp":4:6 -1
     (nil))

(insn 7 6 8 (set (reg:TI 84)
        (mem/c:TI (reg/f:DI 83) [1 a+0 S16 A128])) "/app/example.cpp":4:6 -1
     (nil))


The alignment in the assembly is 16 (128) for both:
        .align 16
        .type   a, @object
        .size   a, 24
a:
        .zero   24

It not obvious what is causing the issue though.

Here is a C++98 testcase that does not depend on C++17 features.=