Re: [patch][middle-end/PR102359]Not add initialization for DECL_VALUE_EXPR variables with -ftrivial-auto-var-init

[Richard Biener <rguenther@suse.de>]

On Tue, 5 Oct 2021, Qing Zhao wrote:

> Hi, 
> 
> This is the patch to fix this issue based on our discussion.
> 
> I have tested it on aarch64 with bootstrap and regtests. X86 bootstrap was done, regtests is ongoing.
> 
> Okay for trunk?
> 
> Thanks.
> 
> Qing
> 
> ======================
> From d349ef0145512efe7f9af2c6bbd01f636475bce3 Mon Sep 17 00:00:00 2001
> From: qing zhao <qing.zhao@oracle.com>
> Date: Mon, 4 Oct 2021 15:26:03 -0700
> Subject: [PATCH] middle-end/102359 Not add initialization for variables that
>  have been  initialized by FEs.
> 
> C++ FE creates proxy variables, which have associated DECL_VALUE_EXPR
> and have been initialized by FE. For such auto variable, we should not
> add initialization when -ftrivial-auto-var-init presents.
> 
> gcc/ChangeLog:
> 
> 2021-10-04  qing zhao  <qing.zhao@oracle.com>
> 
> 	* gimplify.c (is_decl_init_by_fe): New function.
> 	(gimplify_decl_expr): Not add initialization for an auto variable
> 	when it has been initialized by frontend.
> 
> gcc/testsuite/ChangeLog:
> 
> 2021-10-04  qing zhao  <qing.zhao@oracle.com>
> 
> 	* g++.dg/pr102359_1.C: New test.
> 	* g++.dg/pr102359_2.C: New test.
> ---
>  gcc/gimplify.c                    | 21 ++++++++++++++++++++-
>  gcc/testsuite/g++.dg/pr102359_1.C | 13 +++++++++++++
>  gcc/testsuite/g++.dg/pr102359_2.C | 13 +++++++++++++
>  3 files changed, 46 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/pr102359_1.C
>  create mode 100644 gcc/testsuite/g++.dg/pr102359_2.C
> 
> diff --git a/gcc/gimplify.c b/gcc/gimplify.c
> index b27776a..d6865ad 100644
> --- a/gcc/gimplify.c
> +++ b/gcc/gimplify.c
> @@ -1819,6 +1819,19 @@ gimple_add_padding_init_for_auto_var (tree decl, bool is_vla,
>    gimplify_seq_add_stmt (seq_p, call);
>  }
>  
> +/* Return true if the DECL is initialized by FE.
> +   If the VAR_DECL has DECL_VALUE_EXPR that was created by FE (usually C++FE),
> +   it's a proxy varaible, and FE already initializd the DECL_VALUE_EXPR of it.
> +*/
> +static bool
> +is_decl_init_by_fe (tree decl, bool is_created_by_fe)
> +{
> +  if (DECL_HAS_VALUE_EXPR_P (decl)
> +      && is_created_by_fe)
> +    return true;
> +  return false;
> +}
> +
>  /* Return true if the DECL need to be automaticly initialized by the
>     compiler.  */
>  static bool
> @@ -1871,8 +1884,13 @@ gimplify_decl_expr (tree *stmt_p, gimple_seq *seq_p)
>    if (VAR_P (decl) && !DECL_EXTERNAL (decl))
>      {
>        tree init = DECL_INITIAL (decl);
> +      bool is_value_expr_created_by_fe = false;

no need for the = false, it's always initialized below.

>        bool is_vla = false;
>  
> +      /* Check whether a decl has FE created VALUE_EXPR here BEFORE 
> +	 gimplify_vla_decl creates VALUE_EXPR for vla decl.  */
> +      is_value_expr_created_by_fe = DECL_HAS_VALUE_EXPR_P (decl);

That looks a bit weird when looking at ...

> +
>        poly_uint64 size;
>        if (!poly_int_tree_p (DECL_SIZE_UNIT (decl), &size)
>  	  || (!TREE_STATIC (decl)
> @@ -1934,7 +1952,8 @@ gimplify_decl_expr (tree *stmt_p, gimple_seq *seq_p)
>        /* When there is no explicit initializer, if the user requested,
>  	 We should insert an artifical initializer for this automatic
>  	 variable.  */
> -      else if (is_var_need_auto_init (decl))
> +      else if (is_var_need_auto_init (decl)
> +	       && !is_decl_init_by_fe (decl, is_value_expr_created_by_fe))

... which just expands to

 if (DECL_HAS_VALUE_EXPR_P (decl) && DECL_HAS_VALUE_EXPR_P (decl))

can you please name 'is_value_expr_created_by_fe' as
'decl_had_value_expr_p' and check && !decl_had_value_expr_p here?
So sth like

diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index b27776af7c8..9013f385f13 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -1872,6 +1872,7 @@ gimplify_decl_expr (tree *stmt_p, gimple_seq *seq_p)
     {
       tree init = DECL_INITIAL (decl);
       bool is_vla = false;
+      bool decl_had_value_expr_p = DECL_HAS_VALUE_EXPR_P (decl);
 
       poly_uint64 size;
       if (!poly_int_tree_p (DECL_SIZE_UNIT (decl), &size)
@@ -1934,7 +1935,8 @@ gimplify_decl_expr (tree *stmt_p, gimple_seq *seq_p)
       /* When there is no explicit initializer, if the user requested,
         We should insert an artifical initializer for this automatic
         variable.  */
-      else if (is_var_need_auto_init (decl))
+      else if (is_var_need_auto_init (decl)
+              && !decl_had_value_expr_p)
        {
          gimple_add_init_for_auto_var (decl,
                                        flag_auto_var_init,

OK with that change.

Thanks,
Richard.


>  	{
>  	  gimple_add_init_for_auto_var (decl,
>  					flag_auto_var_init,
> diff --git a/gcc/testsuite/g++.dg/pr102359_1.C b/gcc/testsuite/g++.dg/pr102359_1.C
> new file mode 100644
> index 0000000..da643cd
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/pr102359_1.C
> @@ -0,0 +1,13 @@
> +/* PR middle-end/102359 ICE gimplification failed since
> +   r12-3433-ga25e0b5e6ac8a77a.  */
> +/* { dg-do compile } */
> +/* { dg-options "-ftrivial-auto-var-init=zero" } */
> +/* { dg-require-effective-target c++17 } */
> +
> +struct A {
> +  double a = 111;
> +  auto foo() {
> +    return [*this] { return a; };
> +  }
> +};
> +int X = A{}.foo()();
> diff --git a/gcc/testsuite/g++.dg/pr102359_2.C b/gcc/testsuite/g++.dg/pr102359_2.C
> new file mode 100644
> index 0000000..d026d72
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/pr102359_2.C
> @@ -0,0 +1,13 @@
> +/* PR middle-end/102359 ICE gimplification failed since
> +   r12-3433-ga25e0b5e6ac8a77a.  */
> +/* { dg-do run} */
> +/* { dg-options "-ftrivial-auto-var-init=zero" } */
> +/* { dg-require-effective-target c++17 } */
> +
> +int main()
> +{
> + int i = 42;
> + auto l = [=]() mutable { return i; };
> + if (l() != i)
> +   __builtin_abort ();
> +}
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)