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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug d/114171] [13/14 Regression] gdc -O2 -mavx generates misaligned vmovdqa instruction
Date: Fri, 01 Mar 2024 13:37:37 +0000 [thread overview]
Message-ID: <bug-114171-4-hEpUMkb9Ey@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114171-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114171
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Iain Buclaw from comment #4)
> Removed druntime dependency.
> ---
> import gcc.builtins;
> struct Token {
> string label;
> }
> struct BreakStatement {
> ulong pad;
> Token label;
> }
>
> pragma(inline, false)
> auto newclass()
> {
> void *p = __builtin_malloc(BreakStatement.sizeof);
> __builtin_memset(p, 0, BreakStatement.sizeof);
> return cast(BreakStatement*) p;
> }
>
> int main ()
> {
> auto bn = newclass();
> return bn.label is Token.init;
> }
> ---
>
>
>
> Roughly the equivalent C++
> ---
> struct Token {
> struct {
> __SIZE_TYPE__ length;
> const char *ptr;
> } label;
> };
> struct BreakStatement {
> __UINT64_TYPE__ pad;
> Token label;
> };
>
> __attribute__((noinline))
> BreakStatement *newclass()
> {
> void *p = __builtin_malloc(sizeof(BreakStatement));
> __builtin_memset(p, 0, sizeof(BreakStatement));
> return (BreakStatement*) p;
> }
>
> int main ()
> {
> auto bn = newclass();
> auto init = Token();
> return *(__uint128_t*)&bn->label == *(__uint128_t*)&init;
> }
> ---
Unless gdc somehow guarantees bn->label and init are 128bit aligned
then "casting" this way is broken. You can of course use
build_aligned_type to build a properly (mis-)aligned type to use
to dereference to.
next prev parent reply other threads:[~2024-03-01 13:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-29 15:53 [Bug d/114171] New: " a.horodniceanu at proton dot me
2024-03-01 4:59 ` [Bug d/114171] " pinskia at gcc dot gnu.org
2024-03-01 6:28 ` liuhongt at gcc dot gnu.org
2024-03-01 7:05 ` rguenth at gcc dot gnu.org
2024-03-01 8:38 ` a.horodniceanu at proton dot me
2024-03-01 13:25 ` ibuclaw at gdcproject dot org
2024-03-01 13:37 ` rguenth at gcc dot gnu.org [this message]
2024-03-01 14:13 ` ibuclaw at gdcproject dot org
2024-03-03 1:33 ` cvs-commit at gcc dot gnu.org
2024-03-03 1:35 ` cvs-commit at gcc dot gnu.org
2024-03-03 1:37 ` cvs-commit at gcc dot gnu.org
2024-03-03 1:39 ` cvs-commit at gcc dot gnu.org
2024-03-03 1:39 ` ibuclaw at gdcproject dot org
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