On Wed, 11 Aug 2021, Qing Zhao wrote:
>
>
> > On Aug 11, 2021, at 2:02 AM, Richard Biener <rguent...@suse.de> wrote:
> >
> > 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 <rguent...@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.
>
> Yes, it’s an INDIRECT_REF at the point of the failure even though I added a
>
> gimplify_var_or_parm_decl (lhs)
I think the easiest is to build the .DEFERRED_INIT as GENERIC
and use gimplify_assign () to gimplify and add the result
to the sequence. Thus, build a GENERIC CALL_EXPR and then
gimplify_assign (lhs, call_expr, seq);
Richard.
> Qing
>
> >
> >> 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 <rguent...@suse.de>
> > SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> > Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
