> On Aug 10, 2021, at 10:22 AM, Richard Biener <rguent...@suse.de> wrote:
>
> On Tue, 10 Aug 2021, Qing Zhao wrote:
>
>> Hi,
>>
>>> On Aug 10, 2021, at 9:16 AM, Richard Biener <rguent...@suse.de> wrote:
>>>
>>> On Tue, 10 Aug 2021, Qing Zhao wrote:
>>>
>>>>>>>
>>>>>>> +static void
>>>>>>> +expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>>>>>>> +{
>>>>>>> + tree var = gimple_call_lhs (stmt);
>>>>>>> + tree size_of_var = gimple_call_arg (stmt, 0);
>>>>>>> + tree vlaaddr = NULL_TREE;
>>>>>>> + tree var_type = TREE_TYPE (var);
>>>>>>> + bool is_vla = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2));
>>>>>>> + enum auto_init_type init_type
>>>>>>> + = (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (stmt,
>>>>>>> 1));
>>>>>>> +
>>>>>>> + gcc_assert (init_type > AUTO_INIT_UNINITIALIZED);
>>>>>>> +
>>>>>>> + /* if this variable is a VLA, get its SIZE and ADDR first. */
>>>>>>> + if (is_vla)
>>>>>>> + {
>>>>>>> + /* The temporary address variable for this vla should have been
>>>>>>> + created during gimplification phase. Refer to
>>>>>>> gimplify_vla_decl
>>>>>>> + for details. */
>>>>>>> + tree var_decl = (TREE_CODE (var) == SSA_NAME) ?
>>>>>>> + SSA_NAME_VAR (var) : var;
>>>>>>> + gcc_assert (DECL_HAS_VALUE_EXPR_P (var_decl));
>>>>>>> + gcc_assert (TREE_CODE (DECL_VALUE_EXPR (var_decl)) ==
>>>>>>> INDIRECT_REF);
>>>>>>> + /* Get the address of this vla variable. */
>>>>>>> + vlaaddr = TREE_OPERAND (DECL_VALUE_EXPR (var_decl), 0);
>>>>>>>
>>>>>>> err - isn't the address of the decl represented by the LHS
>>>>>>> regardless whether this is a VLA or not?
>>>>>>
>>>>>> The LHS of the call to .DEFERRED_INIT is the DECL itself whatever it’s a
>>>>>> VLA or not.
>>>>>>
>>>>>> In order to create a memset call, we need the Address of this DECL as
>>>>>> the first argument.
>>>>>> If the DECL is not a VLA, we just simply apply “build_fold_addr_expr” on
>>>>>> this DECL to get its address,
>>>>>> However, for VLA, during gimplification phase “gimplify_vla_decl”, we
>>>>>> have already created a temporary
>>>>>> address variable for this DECL, and recorded this address variable with
>>>>>> “DECL_VALUE_EXPR(DECL),
>>>>>> We should use this already created address variable for VLAs.
>>>>>
>>>>> So the issue is that the LHS of the .DEFERRED_INIT call is not properly
>>>>> gimplified. We should not have such decl there but I see we do not
>>>>> have IL verification that covers this.
>>>>
>>>> Don’t quite understand here: do you mean all the LHS of .DEFERRED_INIT
>>>> call are not properly gimplified, or
>>>> Only the LHS of .DEFERRED_INIT call for VLA are not properly gimplified?
>>>
>>> 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.
>
>>>
>>>> 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.
I will try this.
>
> 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.
Okay, I see now.
Will updated the VLA part in gimplify.c and internal-fn.c.
Qing
>
> Richard.
