From: Richard Biener <rguenther@suse.de>
To: Qing Zhao <qing.zhao@oracle.com>
Cc: Jakub Jelinek <jakub@redhat.com>,
Nick Alcock via Gcc-patches <gcc-patches@gcc.gnu.org>,
Kees Cook <keescook@chromium.org>
Subject: Re: [patch][version 6] add -ftrivial-auto-var-init and variable attribute "uninitialized" to gcc
Date: Wed, 11 Aug 2021 09:02:30 +0200 (CEST) [thread overview]
Message-ID: <nycvar.YFH.7.76.2108110900380.11781@zhemvz.fhfr.qr> (raw)
In-Reply-To: <BB83E971-E5CC-4C14-B976-C28AE584798E@oracle.com>
On Tue, 10 Aug 2021, Qing Zhao wrote:
>
>
> > On Aug 10, 2021, at 3:16 PM, Qing Zhao via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> >
> > Hi, Richard,
> >
> >> On Aug 10, 2021, at 10:22 AM, Richard Biener <rguenther@suse.de> wrote:
> >>>>
> >>>> Especially in the VLA case but likely also in general (though unlikely
> >>>> since usually the receiver of initializations are simple enough). I'd
> >>>> expect the VLA case end up as
> >>>>
> >>>> *ptr_to_decl = .DEFERRED_INIT (...);
> >>>>
> >>>> where *ptr_to_decl is the DECL_VALUE_EXPR of the decl.
> >>>
> >>> So, for the following small testing case:
> >>>
> >>> ====
> >>> extern void bar (int);
> >>>
> >>> void foo(int n)
> >>> {
> >>> int arr[n];
> >>> bar (arr[2]);
> >>> return;
> >>> }
> >>> =====
> >>>
> >>> If I compile it with -ftrivial-auto-var-init=zero -fdump-tree-gimple -S -o auto-init-11.s -fdump-rtl-expand, the *.gimple dump is:
> >>>
> >>> =====
> >>> void foo (int n)
> >>> {
> >>> int n.0;
> >>> sizetype D.1950;
> >>> bitsizetype D.1951;
> >>> sizetype D.1952;
> >>> bitsizetype D.1953;
> >>> sizetype D.1954;
> >>> int[0:D.1950] * arr.1;
> >>> void * saved_stack.2;
> >>> int arr[0:D.1950] [value-expr: *arr.1];
> >>>
> >>> saved_stack.2 = __builtin_stack_save ();
> >>> try
> >>> {
> >>> n.0 = n;
> >>> _1 = (long int) n.0;
> >>> _2 = _1 + -1;
> >>> _3 = (sizetype) _2;
> >>> D.1950 = _3;
> >>> _4 = (sizetype) n.0;
> >>> _5 = (bitsizetype) _4;
> >>> _6 = _5 * 32;
> >>> D.1951 = _6;
> >>> _7 = (sizetype) n.0;
> >>> _8 = _7 * 4;
> >>> D.1952 = _8;
> >>> _9 = (sizetype) n.0;
> >>> _10 = (bitsizetype) _9;
> >>> _11 = _10 * 32;
> >>> D.1953 = _11;
> >>> _12 = (sizetype) n.0;
> >>> _13 = _12 * 4;
> >>> D.1954 = _13;
> >>> arr.1 = __builtin_alloca_with_align (D.1954, 32);
> >>> arr = .DEFERRED_INIT (D.1952, 2, 1);
> >>> _14 = (*arr.1)[2];
> >>> bar (_14);
> >>> return;
> >>> }
> >>> finally
> >>> {
> >>> __builtin_stack_restore (saved_stack.2);
> >>> }
> >>> }
> >>>
> >>> ====
> >>>
> >>> You think that the above .DEFEERED_INIT is not correct?
> >>> It should be:
> >>>
> >>> *arr.1 = .DEFERRED_INIT (D.1952. 2, 1);
> >>>
> >>> ?
> >>
> >> Yes.
> >>
> >
> > I updated gimplify.c for VLA and now it emits the call to .DEFERRED_INIT as:
> >
> > arr.1 = __builtin_alloca_with_align (D.1954, 32);
> > *arr.1 = .DEFERRED_INIT (D.1952, 2, 1);
> >
> > However, this call triggered the assertion failure in verify_gimple_call of tree-cfg.c because the LHS is not a valid LHS.
> > Then I modify tree-cfg.c as:
> >
> > diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
> > index 330eb7dd89bf..180d4f1f9e32 100644
> > --- a/gcc/tree-cfg.c
> > +++ b/gcc/tree-cfg.c
> > @@ -3375,7 +3375,11 @@ verify_gimple_call (gcall *stmt)
> > }
> >
> > tree lhs = gimple_call_lhs (stmt);
> > + /* For .DEFERRED_INIT call, the LHS might be an indirection of
> > + a pointer for the VLA variable, which is not a valid LHS of
> > + a gimple call, we ignore the asssertion on this. */
> > if (lhs
> > + && (!gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
> > && (!is_gimple_reg (lhs)
> > && (!is_gimple_lvalue (lhs)
> > || verify_types_in_gimple_reference
> >
> > The assertion failure in tree-cfg.c got resolved, but I got another assertion failure in operands_scanner::get_expr_operands (tree *expr_p, int flags), line 945:
> >
> > 939 /* If we get here, something has gone wrong. */
> > 940 if (flag_checking)
> > 941 {
> > 942 fprintf (stderr, "unhandled expression in get_expr_operands():\n");
> > 943 debug_tree (expr);
> > 944 fputs ("\n", stderr);
> > 945 gcc_unreachable ();
> > 946 }
> >
> > Looks like that the gimple statement:
> > *arr.1 = .DEFERRED_INIT (D.1952, 2, 1);
> >
> > Is not valid. i.e, the LHS should not be an indirection to a pointer.
> >
> > How to resolve this issue?
It sounds like the LHS is an INDIRECT_REF maybe? That means it's
still not properly gimplified because it should end up as a MEM_REF
instead.
But I'm just guessing here ... if you are in a debugger then you can
invoke debug_tree (lhs) in the inferior to see what it exactly is
at the point of the failure.
> I came up with the following solution:
>
> Define the IFN_DEFERRED_INIT function as:
>
> LHS = DEFERRED_INIT (SIZE of the DECL, INIT_TYPE, IS_VLA);
>
> if IS_VLA is false, the LHS is the DECL itself,
> if IS_VLA is true, the LHS is the pointer to this DECL that created by
> gimplify_vla_decl.
>
>
> The benefit of this solution are:
>
> 1. Resolved the invalid IR issue;
> 2. The call stmt carries the address of the VLA natually;
>
> The issue with this solution is:
>
> For VLA and non-VLA, the LHS will be different,
>
> Do you see any other potential issues with this solution?
>
> thanks.
>
> Qing
>
>
>
>
>
--
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
next prev parent reply other threads:[~2021-08-11 7:02 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 3:26 Qing Zhao
2021-07-28 20:21 ` Kees Cook
2021-07-28 21:53 ` Qing Zhao
2021-08-09 14:09 ` Richard Biener
2021-08-09 16:38 ` Qing Zhao
2021-08-09 17:14 ` Richard Biener
2021-08-10 7:36 ` Richard Biener
2021-08-10 13:39 ` Qing Zhao
2021-08-10 14:16 ` Richard Biener
2021-08-10 15:02 ` Qing Zhao
2021-08-10 15:22 ` Richard Biener
2021-08-10 15:55 ` Qing Zhao
2021-08-10 20:16 ` Qing Zhao
2021-08-10 22:26 ` Qing Zhao
2021-08-11 7:02 ` Richard Biener [this message]
2021-08-11 13:33 ` Qing Zhao
2021-08-11 13:37 ` Richard Biener
2021-08-11 13:54 ` Qing Zhao
2021-08-11 13:58 ` Richard Biener
2021-08-11 14:00 ` Qing Zhao
2021-08-11 15:30 ` Qing Zhao
2021-08-11 15:53 ` Richard Biener
2021-08-11 16:22 ` Qing Zhao
2021-08-11 16:55 ` Richard Biener
2021-08-11 16:57 ` Qing Zhao
2021-08-11 20:30 ` Qing Zhao
2021-08-11 22:03 ` Qing Zhao
2021-08-16 7:12 ` Richard Biener
2021-08-16 14:48 ` Qing Zhao
2021-08-16 15:08 ` Richard Biener
2021-08-16 15:39 ` Qing Zhao
2021-08-16 7:11 ` Richard Biener
2021-08-16 16:48 ` Qing Zhao
2021-08-17 15:04 ` Qing Zhao
2021-08-17 20:40 ` Qing Zhao
2021-08-18 7:19 ` Richard Biener
2021-08-18 14:39 ` Qing Zhao
2021-08-11 9:02 ` Richard Sandiford
2021-08-11 13:44 ` Qing Zhao
2021-08-11 16:15 ` Richard Sandiford
2021-08-11 16:29 ` Qing Zhao
2021-08-12 19:24 ` Qing Zhao
2021-08-12 22:45 ` Qing Zhao
2021-08-16 7:40 ` Richard Biener
2021-08-16 15:45 ` Qing Zhao
2021-08-17 8:29 ` Richard Biener
2021-08-17 14:50 ` Qing Zhao
2021-08-17 16:08 ` Qing Zhao
2021-08-18 7:15 ` Richard Biener
2021-08-18 16:02 ` Qing Zhao
2021-08-19 9:00 ` Richard Biener
2021-08-19 13:54 ` Qing Zhao
2021-08-20 14:52 ` Qing Zhao
2021-08-23 13:55 ` Richard Biener
2021-09-02 17:24 ` Qing Zhao
2021-08-16 19:49 ` Qing Zhao
2021-08-17 8:43 ` Richard Biener
2021-08-17 14:03 ` Qing Zhao
2021-08-17 14:45 ` Richard Biener
2021-08-17 14:53 ` Qing Zhao
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