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

[Richard Biener <rguenther@suse.de>]

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

> 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>
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