[patch][version 6] add -ftrivial-auto-var-init and variable attribute "uninitialized" to gcc

Qing Zhao qing.zhao@oracle.com
Wed Aug 18 16:02:17 GMT 2021



> On Aug 18, 2021, at 2:15 AM, Richard Biener <rguenther@suse.de> wrote:
> 
> On Tue, 17 Aug 2021, Qing Zhao wrote:
> 
>> 
>> 
>>> On Aug 17, 2021, at 9:50 AM, Qing Zhao via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>>> 
>>> 
>>> 
>>>> On Aug 17, 2021, at 3:29 AM, Richard Biener <rguenther@suse.de> wrote:
>>>> 
>>>> On Mon, 16 Aug 2021, Qing Zhao wrote:
>>>> 
>>>>> My current code for expand_DEFERRED_INIT is like the following, could you check and see whether there is any issue for it:
>>>>> 
>>>>> #define INIT_PATTERN_VALUE  0xFE
>>>>> static void
>>>>> expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>>>>> {
>>>>> tree lhs = gimple_call_lhs (stmt);
>>>>> tree var_size = gimple_call_arg (stmt, 0);
>>>>> enum auto_init_type init_type
>>>>>  = (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (stmt, 1));
>>>>> bool is_vla = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2));
>>>>> 
>>>>> tree var_type = TREE_TYPE (lhs);
>>>>> gcc_assert (init_type > AUTO_INIT_UNINITIALIZED);
>>>>> 
>>>>> if (is_vla || (!use_register_for_decl (lhs)))
>>>>>  {
>>>>>    if (TREE_CODE (lhs) == SSA_NAME)
>>>>>      lhs = SSA_NAME_VAR (lhs);
>>>> 
>>>> this should not be necessary (in fact you shouldn't see a SSA_NAME
>>>> here, if you do then using SSA_NAME_VAR is wrong)
>>> You mean during RTL expansion phase, all SSA_NAMEs are gone already?
>> 
>> Actually, the lhs could be SSA_NAME here, 
>> 
>> Breakpoint 1, expand_DEFERRED_INIT (stmt=0x7fffe96ae348) at ../../latest-gcc/gcc/internal-fn.c:3021
>> 3021	      mark_addressable (lhs);
>> (gdb) call debug_tree(lhs)
>> <ssa_name 0x7fffe9584e58
>>    type <real_type 0x7fffe959b2a0 float sizes-gimplified SF
>>        size <integer_cst 0x7fffe9579f48 constant 32>
>>        unit-size <integer_cst 0x7fffe9579f60 constant 4>
>>        align:32 warn_if_not_align:0 symtab:0 alias-set 2 canonical-type 0x7fffe959b2a0 precision:32
>>        pointer_to_this <pointer_type 0x7fffe959b7e0>>
>>    visited var <var_decl 0x7ffff7ff7bd0 temp1>
>>    def_stmt temp1_5 = .DEFERRED_INIT (4, 2, 0, &"temp1"[0]);
>>    version:5>
>> 
>> when I deleted:
>> 
>> if (TREE_CODE (lhs) == SSA_NAME
>>   lhs = SSA_NAME_VAR (lhs);
> 
> but then using SSA_NAME_VAR is broken.  I suspect use_register_for_decl
> isn't the correct thing to look at.  I think we need to look at what
> the LHS expanded to if it is a SSA_VAR_P (that includes SSA names
> but also plain DECLs but not what we get from VLAs where we'd see
> *ptr).  So sth like
> 
>  bool reg_lhs;
>  if (SSA_VAR_P (lhs))
>    {
>      rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
>      reg_lhs = !MEM_P (tem);
>      /* If not MEM_P reg_lhs should be REG_P or SUBREG_P (but maybe
>         also CONCAT or lowpart...?)  */
>    }
>  else
>    {
>      gcc_assert (is_vla);
>      reg_lhs = false;
>    }
> 
>  if (!reg_lhs)
>    memset path
>  else
>    expand_assignment path

After making the following change:

+  bool reg_lhs = true;
 
   tree var_type = TREE_TYPE (lhs);
   gcc_assert (init_type > AUTO_INIT_UNINITIALIZED);
 
-  if (is_vla || (!use_register_for_decl (lhs)))
+  if (SSA_VAR_P (lhs))
+    {
+      rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
+      reg_lhs = !MEM_P (tem);
+    }
+  else
+    {
+      gcc_assert (is_vla);
+      reg_lhs = false;
+    }
+
+  if (!reg_lhs)
     {

I got exactly the same internal error that failed at expr.c:

 8436   /* We must have made progress.  */
 8437   gcc_assert (inner != exp);


Looks like for the following code:

3026   if (!reg_lhs)
3027     {
3028     /* If this is a VLA or the variable is not in register,
3029        expand to a memset to initialize it.  */
3030       mark_addressable (lhs);
3031       tree var_addr = build_fold_addr_expr (lhs);
3032 
3033       tree value = (init_type == AUTO_INIT_PATTERN) ?
3034                     build_int_cst (integer_type_node,
3035                                    INIT_PATTERN_VALUE) :
3036                     integer_zero_node;
3037       tree m_call = build_call_expr (builtin_decl_implicit (BUILT_IN_MEMSET),
3038                                      3, var_addr, value, var_size);
3039       /* Expand this memset call.  */
3040       expand_builtin_memset (m_call, NULL_RTX, TYPE_MODE (var_type));
3041     }

At line 3030, “lhs” could be a SSA_NAME.

My questions are:

1. Could the routine “mark_addressable” and “build_fold_addr_expr” be applied on SSA_NAME?
2. Could the routine “expand_builtin_memset” be applied on the memset call whose “DEST” is
    an address expression on SSA_NAME? 
3. Within “expand_DEFERRED_INIT”, can I call “expand_builtin_memset” to expand .DEFERRED_INIT?

I suspect that one of the above 3 might be the issue, but not sure which one?

Thanks a lot.

Qing
   


> bool reg_lhs;
>  if (SSA_VAR_P (lhs))
>    {
>      rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
>      reg_lhs = !MEM_P (tem);
>      /* If not MEM_P reg_lhs should be REG_P or SUBREG_P (but maybe
>         also CONCAT or lowpart...?)  */
>    }
>  else
>    {
>      gcc_assert (is_vla);
>      reg_lhs = false;
>    }


> 
>> Many testing cases failed with internal compiler error:
>> 
>> /home/opc/Work/GCC/latest-gcc/gcc/testsuite/c-c++-common/auto-init-3.c:9:9: internal compiler error: in expand_expr_addr_expr_1, at expr.c:8437
>> 0xe237aa expand_expr_addr_expr_1
>> 	../../latest-gcc/gcc/expr.c:8437
>> 0xe24059 expand_expr_addr_expr
>> 	../../latest-gcc/gcc/expr.c:8525
>> 0xe32b56 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
>> 	../../latest-gcc/gcc/expr.c:11741
>> 0xe2da52 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
>> 	../../latest-gcc/gcc/expr.c:10777
>> 0xe24706 expand_expr_real(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
>> 	../../latest-gcc/gcc/expr.c:8713
>> 0xc13f15 expand_expr
>> 	../../latest-gcc/gcc/expr.h:301
>> 0xc17acb get_memory_rtx
>> 	../../latest-gcc/gcc/builtins.c:1370
>> 0xc2223d expand_builtin_memset_args
>> 	../../latest-gcc/gcc/builtins.c:4102
>> 0xc21a20 expand_builtin_memset(tree_node*, rtx_def*, machine_mode)
>> 	../../latest-gcc/gcc/builtins.c:3886
>> 0xfb5c85 expand_DEFERRED_INIT
>> 	../../latest-gcc/gcc/internal-fn.c:3031
>> 
>> 
>> So, did I do anything wrong?
>> 
>> Qing
> 
> -- 
> Richard Biener <rguenther@suse.de>
> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)



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