> 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?
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
