Hi, Richard,
> On Aug 10, 2021, at 10:22 AM, Richard Biener <[email protected]> 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?
Thanks a lot for your help.
Qing
>>>
>>>> What do you mean by “such” decl? A decl whole “DECL_VALUE_EXPR(DECL)” is
>>>> valid?
>>>
>>> A 'decl' that has a DECL_VALUE_EXPR should not appear in the IL, it should
>>> always be refered to as its DECL_VALUE_EXPR.
>>
>> Okay.
>
> I'm going to test
>
> diff --git a/gcc/tree-ssa-operands.c b/gcc/tree-ssa-operands.c
> index ebf7eea3b04..15c73b6d6f4 100644
> --- a/gcc/tree-ssa-operands.c
> +++ b/gcc/tree-ssa-operands.c
> @@ -799,10 +799,11 @@ operands_scanner::get_expr_operands (tree *expr_p,
> int flags)
> flags | opf_not_non_addressable |
> opf_address_taken);
> return;
>
> - case SSA_NAME:
> case VAR_DECL:
> case PARM_DECL:
> case RESULT_DECL:
> + gcc_checking_assert (!DECL_HAS_VALUE_EXPR_P (expr));
> + case SSA_NAME:
> case STRING_CST:
> case CONST_DECL:
> if (!(flags & opf_address_taken))
>
> which should pass on unmodified trunk (fingers crossing ;)), but
> it would likely trip on the current -ftrivial-auto-init patch.
>
> The issue with the current IL is that nothing keeps arr.1 live
> and thus the allocation could be DCEd but the .DEFERRED_INIT
> call would remain, eventually being expanded to zero storage
> that isn't there.
>
> Richard.
