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Subject: [Bug target/101023] [11/12 Regression] wrong code with -mstackrealign
Date: Fri, 11 Jun 2021 12:25:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101023

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-06-11
             Status|UNCONFIRMED                 |WAITING

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Zdenek Sojka from comment #0)
> Created attachment 50981 [details]
> auto-reduced testcase (from OpenTTD sources)
>=20
> Compiler output:
> $ x86_64-pc-linux-gnu-g++ -O2 -mtune=3Dopteron -mstackrealign
> --param=3Dhot-bb-frequency-fraction=3D1 testcase.C -S
>=20
> The offending code is:
> .L8:
> 	pushq	%rbp
> 	.cfi_def_cfa_offset 16
> 	.cfi_offset 6, -16
> 	movq	%rsp, %rbp
> 	.cfi_def_cfa_register 6
> 	movq	%r12, -8(%rbp)
> 	pushq	%rax
>=20
> the "push" overwrites r12 stored just one instruction above; when returni=
ng:
> 	movq	-8(%rbp), %r12
> 	xorl	%eax, %eax
> 	leave
> 	.cfi_def_cfa 7, 8
> 	ret
>=20
> the wrong data is restored to r12
>=20
> I wasn't able yet to generate an executable testcase, but I can try to if
> needed. (it shouldn't be that hard, just r12 needs to be used by the call=
er
> during the call)

Please create a run-time testcase.=