[2/2,middle-end/102276] Adding -Wtrivial-auto-var-init and update documentation.

  Hi,

This is the 2nd patch for fixing pr102276.

Adding -Wtrivial-auto-var-init and update documentation.

Adding a new warning option -Wtrivial-auto-var-init to report cases when
-ftrivial-auto-var-init cannot initialize the auto variable. At the same
time, update documentation for -ftrivial-auto-var-init to connect it with
the new warning option -Wtrivial-auto-var-init,  and add documentation
for -Wtrivial-auto-var-init.

Bootstraped and regression tested on both x86 and aarch64.

Okay for committing?

thanks.

Qing.

==============================
From 4346890b8f4258489c4841f1992ba3ce816d7689 Mon Sep 17 00:00:00 2001
From: Qing Zhao <qing.zhao@oracle.com>
Date: Fri, 18 Feb 2022 15:53:15 +0000
Subject: [PATCH 2/2] Adding -Wtrivial-auto-var-init and update documentation.

Adding a new warning option -Wtrivial-auto-var-init to report cases when
-ftrivial-auto-var-init cannot initialize the auto variable. At the same
time, update documentation for -ftrivial-auto-var-init to connect it with
the new warning option -Wtrivial-auto-var-init,  and add documentation
for -Wtrivial-auto-var-init.

2022-02-18 Qing Zhao  <qing.zhao@oracle.com>
gcc/ChangeLog:

	* common.opt (-Wtrivial-auto-var-init): New option.
	* doc/invoke.texi (-Wtrivial-auto-var-init): Document new option.
	(-ftrivial-auto-var-init): Update option;
	* gimplify.cc (maybe_warn_switch_unreachable): Rename...
	(maybe_warn_switch_unreachable_and_auto_init): ...to this.
	(gimplify_switch_expr): Call new function.

gcc/testsuite/ChangeLog:

	* gcc.dg/auto-init-pr102276-3.c: New test.
	* gcc.dg/auto-init-pr102276-4.c: New test.
---
 gcc/common.opt                              |   4 +
 gcc/doc/invoke.texi                         |  14 ++-
 gcc/gimplify.cc                             | 100 +++++++++++++++-----
 gcc/testsuite/gcc.dg/auto-init-pr102276-3.c |  40 ++++++++
 gcc/testsuite/gcc.dg/auto-init-pr102276-4.c |  40 ++++++++
 5 files changed, 175 insertions(+), 23 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
 create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
  

On Sat, 19 Feb 2022, Qing Zhao wrote:

> Hi,
> 
> This is the 2nd patch for fixing pr102276.
> 
> Adding -Wtrivial-auto-var-init and update documentation.
> 
> Adding a new warning option -Wtrivial-auto-var-init to report cases when
> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
> time, update documentation for -ftrivial-auto-var-init to connect it with
> the new warning option -Wtrivial-auto-var-init,  and add documentation
> for -Wtrivial-auto-var-init.
> 
> Bootstraped and regression tested on both x86 and aarch64.
> 
> Okay for committing?
> 
> thanks.
> 
> Qing.
> 
> ==============================
> From 4346890b8f4258489c4841f1992ba3ce816d7689 Mon Sep 17 00:00:00 2001
> From: Qing Zhao <qing.zhao@oracle.com>
> Date: Fri, 18 Feb 2022 15:53:15 +0000
> Subject: [PATCH 2/2] Adding -Wtrivial-auto-var-init and update documentation.
> 
> Adding a new warning option -Wtrivial-auto-var-init to report cases when
> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
> time, update documentation for -ftrivial-auto-var-init to connect it with
> the new warning option -Wtrivial-auto-var-init,  and add documentation
> for -Wtrivial-auto-var-init.
> 
> 2022-02-18 Qing Zhao  <qing.zhao@oracle.com>
> gcc/ChangeLog:
> 
> 	* common.opt (-Wtrivial-auto-var-init): New option.
> 	* doc/invoke.texi (-Wtrivial-auto-var-init): Document new option.
> 	(-ftrivial-auto-var-init): Update option;
> 	* gimplify.cc (maybe_warn_switch_unreachable): Rename...
> 	(maybe_warn_switch_unreachable_and_auto_init): ...to this.
> 	(gimplify_switch_expr): Call new function.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.dg/auto-init-pr102276-3.c: New test.
> 	* gcc.dg/auto-init-pr102276-4.c: New test.
> ---
>  gcc/common.opt                              |   4 +
>  gcc/doc/invoke.texi                         |  14 ++-
>  gcc/gimplify.cc                             | 100 +++++++++++++++-----
>  gcc/testsuite/gcc.dg/auto-init-pr102276-3.c |  40 ++++++++
>  gcc/testsuite/gcc.dg/auto-init-pr102276-4.c |  40 ++++++++
>  5 files changed, 175 insertions(+), 23 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>  create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
> 
> diff --git a/gcc/common.opt b/gcc/common.opt
> index c21e5273ae3..22c95dbfa49 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -801,6 +801,10 @@ Wtrampolines
>  Common Var(warn_trampolines) Warning
>  Warn whenever a trampoline is generated.
>  
> +Wtrivial-auto-var-init
> +Common Var(warn_trivial_auto_var_init) Warning Init(0)
> +Warn about where -ftrivial-auto-var-init cannot initialize the auto variable.
> +

Warn about cases where ... initialize a variable.

>  Wtype-limits
>  Common Var(warn_type_limits) Warning EnabledBy(Wextra)
>  Warn if a comparison is always true or always false due to the limited range of the data type.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index e1a00c80307..c61a5b4b4a5 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -399,7 +399,7 @@ Objective-C and Objective-C++ Dialects}.
>  -Wswitch  -Wno-switch-bool  -Wswitch-default  -Wswitch-enum @gol
>  -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand @gol
>  -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
> --Wtsan -Wtype-limits  -Wundef @gol
> +-Wtrivial-auto-var-init -Wtsan -Wtype-limits  -Wundef @gol
>  -Wuninitialized  -Wunknown-pragmas @gol
>  -Wunsuffixed-float-constants  -Wunused @gol
>  -Wunused-but-set-parameter  -Wunused-but-set-variable @gol
> @@ -6953,6 +6953,14 @@ This warning is enabled by default for C and C++ programs.
>  Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
>  built-in functions are used.  These functions changed semantics in GCC 4.4.
>  
> +@item -Wtrivial-auto-var-init
> +@opindex Wtrivial-auto-var-init
> +@opindex Wno-trivial-auto-var-init
> +Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic
> +variable.  A common situation is an automatic variable that is declared
> +between the controlling expression and the first case lable of a @code{switch}
> +statement.
> +
>  @item -Wunused-but-set-parameter
>  @opindex Wunused-but-set-parameter
>  @opindex Wno-unused-but-set-parameter
> @@ -12314,6 +12322,10 @@ initializer as uninitialized, @option{-Wuninitialized} and
>  warning messages on such automatic variables.
>  With this option, GCC will also initialize any padding of automatic variables
>  that have structure or union types to zeroes.
> +However, the current implementation cannot initialize automatic variables that
> +are declared between the controlling expression and the first case of a
> +@code{switch} statement.  Using @option{-Wtrivial-auto-var-init} to report all
> +such cases.
>  
>  The three values of @var{choice} are:
>  
> diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
> index 4e3bbf5314d..7e52794691f 100644
> --- a/gcc/gimplify.cc
> +++ b/gcc/gimplify.cc
> @@ -2079,13 +2079,59 @@ warn_switch_unreachable_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
>    return NULL_TREE;
>  }
>  
> +/* Callback for walk_gimple_seq.  */
> +
> +static tree
> +warn_switch_unreachable_auto_init_r (gimple_stmt_iterator *gsi_p,
> +				     bool *handled_ops_p,
> +				     struct walk_stmt_info *)
> +{
> +  gimple *stmt = gsi_stmt (*gsi_p);
> +
> +  *handled_ops_p = true;
> +  switch (gimple_code (stmt))
> +    {
> +    case GIMPLE_TRY:
> +    case GIMPLE_BIND:
> +    case GIMPLE_CATCH:
> +    case GIMPLE_EH_FILTER:
> +    case GIMPLE_TRANSACTION:
> +      /* Walk the sub-statements.  */
> +      *handled_ops_p = false;
> +      break;
> +    case GIMPLE_CALL:
> +      if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)
> +	  && flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> +	{
> +	  /* Get the variable name from the 3rd argument of call.  */
> +	  tree var_name = gimple_call_arg (stmt, 2);
> +	  var_name = TREE_OPERAND (TREE_OPERAND (var_name, 0), 0);
> +	  const char *var_name_str = TREE_STRING_POINTER (var_name);
> +
> +	  warning_at (gimple_location (stmt), OPT_Wtrivial_auto_var_init,
> +		      "%qs cannot be initialized with"
> +		      "%<-ftrivial-auto-var_init%>",
> +		      var_name_str);
> +	}
> +      break;
> +    case GIMPLE_LABEL:
> +      /* Stop till the first Label.  */
> +      return integer_zero_node;
> +    default:
> +      break;
> +    }
> +  return NULL_TREE;
> +}
> +
>  /* Possibly warn about unreachable statements between switch's controlling
> -   expression and the first case.  SEQ is the body of a switch expression.  */
> +   expression and the first case.  Also warn about -ftrivial-auto-var-init
> +   cannot initialize the auto variable under such situation.
> +   SEQ is the body of a switch expression.  */
>  
>  static void
> -maybe_warn_switch_unreachable (gimple_seq seq)
> +maybe_warn_switch_unreachable_and_auto_init (gimple_seq seq)
>  {
> -  if (!warn_switch_unreachable
> +  if ((!warn_switch_unreachable && !warn_trivial_auto_var_init)
>        /* This warning doesn't play well with Fortran when optimizations
>  	 are on.  */
>        || lang_GNU_Fortran ()
> @@ -2093,26 +2139,36 @@ maybe_warn_switch_unreachable (gimple_seq seq)
>      return;
>  
>    struct walk_stmt_info wi;
> -  memset (&wi, 0, sizeof (wi));
> -  walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
> -  gimple *stmt = (gimple *) wi.info;
>  
> -  if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
> +  if (warn_switch_unreachable)
>      {
> -      if (gimple_code (stmt) == GIMPLE_GOTO
> -	  && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
> -	  && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
> -	/* Don't warn for compiler-generated gotos.  These occur
> -	   in Duff's devices, for example.  */
> -	;
> -      else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> -		&& (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
> -	/* Don't warn for compiler-generated initializations for
> -	  -ftrivial-auto-var-init.  */
> -	;
> -      else
> -	warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
> -		    "statement will never be executed");
> +      memset (&wi, 0, sizeof (wi));
> +      walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
> +      gimple *stmt = (gimple *) wi.info;
> +
> +      if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
> +	{
> +	  if (gimple_code (stmt) == GIMPLE_GOTO
> +	      && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
> +	      && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
> +	  /* Don't warn for compiler-generated gotos.  These occur
> +	     in Duff's devices, for example.  */
> +	    ;
> +	  else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> +		   && (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
> +	  /* Don't warn for compiler-generated initializations for
> +	     -ftrivial-auto-var-init.  */
> +	    ;
> +	  else
> +	    warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
> +			"statement will never be executed");
> +	}
> +    }

Hmm.  I'd re-organize the code to emit both the Wswitch-unreachable 
and -Wtrivial_auto_var_init diagnostic from the existing
warn_switch_unreachable_r callback.  You can use wi.info to keep
track whether a Wswitch-unreachable diagnostic was already emitted
(and if -Wtrivial_auto_var_init is not enabled abort the walk)
for example.

Thanks,
Richard.

> +  if (warn_trivial_auto_var_init)
> +    {
> +      memset (&wi, 0, sizeof (wi));
> +      walk_gimple_seq (seq, warn_switch_unreachable_auto_init_r, NULL, &wi);
>      }
>  }
>  
> @@ -2646,7 +2702,7 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
>        gimplify_stmt (&SWITCH_BODY (switch_expr), &switch_body_seq);
>  
>        gimplify_ctxp->in_switch_expr = old_in_switch_expr;
> -      maybe_warn_switch_unreachable (switch_body_seq);
> +      maybe_warn_switch_unreachable_and_auto_init (switch_body_seq);
>        maybe_warn_implicit_fallthrough (switch_body_seq);
>        /* Only do this for the outermost GIMPLE_SWITCH.  */
>        if (!gimplify_ctxp->in_switch_expr)
> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
> new file mode 100644
> index 00000000000..f113f46e29d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
> @@ -0,0 +1,40 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=zero" } */
> +
> +int g(int *, int *);
> +int f()
> +{
> +    switch (0) {
> +        int x;  /* { dg-warning "cannot be initialized with" } */
> +        int y;  /* { dg-warning "cannot be initialized with" } */
> +        default:
> +        return g(&x, &y);
> +    }
> +}
> +
> +int g1(int, int);
> +int f1()
> +{
> +    switch (0) {
> +        int x; /* { dg-warning "cannot be initialized with" } */
> +        int y; /* { dg-warning "cannot be initialized with" } */
> +        default:
> +        return g1(x, y);
> +    }
> +}
> +
> +struct S
> +{
> +  char a;
> +  int b;
> +};
> +int g2(int);
> +int f2(int input)
> +{
> +    switch (0) {
> +        struct S x; /* { dg-warning "cannot be initialized with" } */
> +        struct S y; /* { dg-warning "cannot be initialized with" } */
> +        default:
> +        return g2(input) + x.b + y.b;
> +    }
> +}
> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
> new file mode 100644
> index 00000000000..662e0d1182e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
> @@ -0,0 +1,40 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=pattern" } */
> +
> +int g(int *, int *);
> +int f()
> +{
> +    switch (0) {
> +        int x;  /* { dg-warning "cannot be initialized with" } */
> +        int y;  /* { dg-warning "cannot be initialized with" } */
> +        default:
> +        return g(&x, &y);
> +    }
> +}
> +
> +int g1(int, int);
> +int f1()
> +{
> +    switch (0) {
> +        int x; /* { dg-warning "cannot be initialized with" } */
> +        int y; /* { dg-warning "cannot be initialized with" } */
> +        default:
> +        return g1(x, y);
> +    }
> +}
> +
> +struct S
> +{
> +  char a;
> +  int b;
> +};
> +int g2(int);
> +int f2(int input)
> +{
> +    switch (0) {
> +        struct S x; /* { dg-warning "cannot be initialized with" } */
> +        struct S y; /* { dg-warning "cannot be initialized with" } */
> +        default:
> +        return g2(input) + x.b + y.b;
> +    }
> +}
>
  

> On Feb 24, 2022, at 4:16 AM, Richard Biener <rguenther@suse.de> wrote:
> 
> On Sat, 19 Feb 2022, Qing Zhao wrote:
> 
>> Hi,
>> 
>> This is the 2nd patch for fixing pr102276.
>> 
>> Adding -Wtrivial-auto-var-init and update documentation.
>> 
>> Adding a new warning option -Wtrivial-auto-var-init to report cases when
>> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
>> time, update documentation for -ftrivial-auto-var-init to connect it with
>> the new warning option -Wtrivial-auto-var-init,  and add documentation
>> for -Wtrivial-auto-var-init.
>> 
>> Bootstraped and regression tested on both x86 and aarch64.
>> 
>> Okay for committing?
>> 
>> thanks.
>> 
>> Qing.
>> 
>> ==============================
>> From 4346890b8f4258489c4841f1992ba3ce816d7689 Mon Sep 17 00:00:00 2001
>> From: Qing Zhao <qing.zhao@oracle.com>
>> Date: Fri, 18 Feb 2022 15:53:15 +0000
>> Subject: [PATCH 2/2] Adding -Wtrivial-auto-var-init and update documentation.
>> 
>> Adding a new warning option -Wtrivial-auto-var-init to report cases when
>> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
>> time, update documentation for -ftrivial-auto-var-init to connect it with
>> the new warning option -Wtrivial-auto-var-init,  and add documentation
>> for -Wtrivial-auto-var-init.
>> 
>> 2022-02-18 Qing Zhao  <qing.zhao@oracle.com>
>> gcc/ChangeLog:
>> 
>> 	* common.opt (-Wtrivial-auto-var-init): New option.
>> 	* doc/invoke.texi (-Wtrivial-auto-var-init): Document new option.
>> 	(-ftrivial-auto-var-init): Update option;
>> 	* gimplify.cc (maybe_warn_switch_unreachable): Rename...
>> 	(maybe_warn_switch_unreachable_and_auto_init): ...to this.
>> 	(gimplify_switch_expr): Call new function.
>> 
>> gcc/testsuite/ChangeLog:
>> 
>> 	* gcc.dg/auto-init-pr102276-3.c: New test.
>> 	* gcc.dg/auto-init-pr102276-4.c: New test.
>> ---
>> gcc/common.opt                              |   4 +
>> gcc/doc/invoke.texi                         |  14 ++-
>> gcc/gimplify.cc                             | 100 +++++++++++++++-----
>> gcc/testsuite/gcc.dg/auto-init-pr102276-3.c |  40 ++++++++
>> gcc/testsuite/gcc.dg/auto-init-pr102276-4.c |  40 ++++++++
>> 5 files changed, 175 insertions(+), 23 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
>> 
>> diff --git a/gcc/common.opt b/gcc/common.opt
>> index c21e5273ae3..22c95dbfa49 100644
>> --- a/gcc/common.opt
>> +++ b/gcc/common.opt
>> @@ -801,6 +801,10 @@ Wtrampolines
>> Common Var(warn_trampolines) Warning
>> Warn whenever a trampoline is generated.
>> 
>> +Wtrivial-auto-var-init
>> +Common Var(warn_trivial_auto_var_init) Warning Init(0)
>> +Warn about where -ftrivial-auto-var-init cannot initialize the auto variable.
>> +
> 
> Warn about cases where ... initialize a variable.

Okay. 

> 
>> Wtype-limits
>> Common Var(warn_type_limits) Warning EnabledBy(Wextra)
>> Warn if a comparison is always true or always false due to the limited range of the data type.
>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>> index e1a00c80307..c61a5b4b4a5 100644
>> --- a/gcc/doc/invoke.texi
>> +++ b/gcc/doc/invoke.texi
>> @@ -399,7 +399,7 @@ Objective-C and Objective-C++ Dialects}.
>> -Wswitch  -Wno-switch-bool  -Wswitch-default  -Wswitch-enum @gol
>> -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand @gol
>> -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
>> --Wtsan -Wtype-limits  -Wundef @gol
>> +-Wtrivial-auto-var-init -Wtsan -Wtype-limits  -Wundef @gol
>> -Wuninitialized  -Wunknown-pragmas @gol
>> -Wunsuffixed-float-constants  -Wunused @gol
>> -Wunused-but-set-parameter  -Wunused-but-set-variable @gol
>> @@ -6953,6 +6953,14 @@ This warning is enabled by default for C and C++ programs.
>> Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
>> built-in functions are used.  These functions changed semantics in GCC 4.4.
>> 
>> +@item -Wtrivial-auto-var-init
>> +@opindex Wtrivial-auto-var-init
>> +@opindex Wno-trivial-auto-var-init
>> +Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic
>> +variable.  A common situation is an automatic variable that is declared
>> +between the controlling expression and the first case lable of a @code{switch}
>> +statement.
>> +
>> @item -Wunused-but-set-parameter
>> @opindex Wunused-but-set-parameter
>> @opindex Wno-unused-but-set-parameter
>> @@ -12314,6 +12322,10 @@ initializer as uninitialized, @option{-Wuninitialized} and
>> warning messages on such automatic variables.
>> With this option, GCC will also initialize any padding of automatic variables
>> that have structure or union types to zeroes.
>> +However, the current implementation cannot initialize automatic variables that
>> +are declared between the controlling expression and the first case of a
>> +@code{switch} statement.  Using @option{-Wtrivial-auto-var-init} to report all
>> +such cases.
>> 
>> The three values of @var{choice} are:
>> 
>> diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
>> index 4e3bbf5314d..7e52794691f 100644
>> --- a/gcc/gimplify.cc
>> +++ b/gcc/gimplify.cc
>> @@ -2079,13 +2079,59 @@ warn_switch_unreachable_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
>>   return NULL_TREE;
>> }
>> 
>> +/* Callback for walk_gimple_seq.  */
>> +
>> +static tree
>> +warn_switch_unreachable_auto_init_r (gimple_stmt_iterator *gsi_p,
>> +				     bool *handled_ops_p,
>> +				     struct walk_stmt_info *)
>> +{
>> +  gimple *stmt = gsi_stmt (*gsi_p);
>> +
>> +  *handled_ops_p = true;
>> +  switch (gimple_code (stmt))
>> +    {
>> +    case GIMPLE_TRY:
>> +    case GIMPLE_BIND:
>> +    case GIMPLE_CATCH:
>> +    case GIMPLE_EH_FILTER:
>> +    case GIMPLE_TRANSACTION:
>> +      /* Walk the sub-statements.  */
>> +      *handled_ops_p = false;
>> +      break;
>> +    case GIMPLE_CALL:
>> +      if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)
>> +	  && flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
>> +	{
>> +	  /* Get the variable name from the 3rd argument of call.  */
>> +	  tree var_name = gimple_call_arg (stmt, 2);
>> +	  var_name = TREE_OPERAND (TREE_OPERAND (var_name, 0), 0);
>> +	  const char *var_name_str = TREE_STRING_POINTER (var_name);
>> +
>> +	  warning_at (gimple_location (stmt), OPT_Wtrivial_auto_var_init,
>> +		      "%qs cannot be initialized with"
>> +		      "%<-ftrivial-auto-var_init%>",
>> +		      var_name_str);
>> +	}
>> +      break;
>> +    case GIMPLE_LABEL:
>> +      /* Stop till the first Label.  */
>> +      return integer_zero_node;
>> +    default:
>> +      break;
>> +    }
>> +  return NULL_TREE;
>> +}
>> +
>> /* Possibly warn about unreachable statements between switch's controlling
>> -   expression and the first case.  SEQ is the body of a switch expression.  */
>> +   expression and the first case.  Also warn about -ftrivial-auto-var-init
>> +   cannot initialize the auto variable under such situation.
>> +   SEQ is the body of a switch expression.  */
>> 
>> static void
>> -maybe_warn_switch_unreachable (gimple_seq seq)
>> +maybe_warn_switch_unreachable_and_auto_init (gimple_seq seq)
>> {
>> -  if (!warn_switch_unreachable
>> +  if ((!warn_switch_unreachable && !warn_trivial_auto_var_init)
>>       /* This warning doesn't play well with Fortran when optimizations
>> 	 are on.  */
>>       || lang_GNU_Fortran ()
>> @@ -2093,26 +2139,36 @@ maybe_warn_switch_unreachable (gimple_seq seq)
>>     return;
>> 
>>   struct walk_stmt_info wi;
>> -  memset (&wi, 0, sizeof (wi));
>> -  walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
>> -  gimple *stmt = (gimple *) wi.info;
>> 
>> -  if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
>> +  if (warn_switch_unreachable)
>>     {
>> -      if (gimple_code (stmt) == GIMPLE_GOTO
>> -	  && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
>> -	  && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
>> -	/* Don't warn for compiler-generated gotos.  These occur
>> -	   in Duff's devices, for example.  */
>> -	;
>> -      else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
>> -		&& (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
>> -	/* Don't warn for compiler-generated initializations for
>> -	  -ftrivial-auto-var-init.  */
>> -	;
>> -      else
>> -	warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
>> -		    "statement will never be executed");
>> +      memset (&wi, 0, sizeof (wi));
>> +      walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
>> +      gimple *stmt = (gimple *) wi.info;
>> +
>> +      if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
>> +	{
>> +	  if (gimple_code (stmt) == GIMPLE_GOTO
>> +	      && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
>> +	      && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
>> +	  /* Don't warn for compiler-generated gotos.  These occur
>> +	     in Duff's devices, for example.  */
>> +	    ;
>> +	  else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
>> +		   && (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
>> +	  /* Don't warn for compiler-generated initializations for
>> +	     -ftrivial-auto-var-init.  */
>> +	    ;
>> +	  else
>> +	    warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
>> +			"statement will never be executed");
>> +	}
>> +    }
> 
> Hmm.  I'd re-organize the code to emit both the Wswitch-unreachable 
> and -Wtrivial_auto_var_init diagnostic from the existing
> warn_switch_unreachable_r callback.  You can use wi.info to keep
> track whether a Wswitch-unreachable diagnostic was already emitted
> (and if -Wtrivial_auto_var_init is not enabled abort the walk)
> for example.

Okay. Will try this.

A question here: for the current -Wswitch-unreachable, the warning will be emit only once for the first unreachable stmt. 
Shall we emit warning for each unreachable stmt instead?

thanks.

Qing
> 
> Thanks,
> Richard.
> 
>> +  if (warn_trivial_auto_var_init)
>> +    {
>> +      memset (&wi, 0, sizeof (wi));
>> +      walk_gimple_seq (seq, warn_switch_unreachable_auto_init_r, NULL, &wi);
>>     }
>> }
>> 
>> @@ -2646,7 +2702,7 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
>>       gimplify_stmt (&SWITCH_BODY (switch_expr), &switch_body_seq);
>> 
>>       gimplify_ctxp->in_switch_expr = old_in_switch_expr;
>> -      maybe_warn_switch_unreachable (switch_body_seq);
>> +      maybe_warn_switch_unreachable_and_auto_init (switch_body_seq);
>>       maybe_warn_implicit_fallthrough (switch_body_seq);
>>       /* Only do this for the outermost GIMPLE_SWITCH.  */
>>       if (!gimplify_ctxp->in_switch_expr)
>> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>> new file mode 100644
>> index 00000000000..f113f46e29d
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>> @@ -0,0 +1,40 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=zero" } */
>> +
>> +int g(int *, int *);
>> +int f()
>> +{
>> +    switch (0) {
>> +        int x;  /* { dg-warning "cannot be initialized with" } */
>> +        int y;  /* { dg-warning "cannot be initialized with" } */
>> +        default:
>> +        return g(&x, &y);
>> +    }
>> +}
>> +
>> +int g1(int, int);
>> +int f1()
>> +{
>> +    switch (0) {
>> +        int x; /* { dg-warning "cannot be initialized with" } */
>> +        int y; /* { dg-warning "cannot be initialized with" } */
>> +        default:
>> +        return g1(x, y);
>> +    }
>> +}
>> +
>> +struct S
>> +{
>> +  char a;
>> +  int b;
>> +};
>> +int g2(int);
>> +int f2(int input)
>> +{
>> +    switch (0) {
>> +        struct S x; /* { dg-warning "cannot be initialized with" } */
>> +        struct S y; /* { dg-warning "cannot be initialized with" } */
>> +        default:
>> +        return g2(input) + x.b + y.b;
>> +    }
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
>> new file mode 100644
>> index 00000000000..662e0d1182e
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
>> @@ -0,0 +1,40 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=pattern" } */
>> +
>> +int g(int *, int *);
>> +int f()
>> +{
>> +    switch (0) {
>> +        int x;  /* { dg-warning "cannot be initialized with" } */
>> +        int y;  /* { dg-warning "cannot be initialized with" } */
>> +        default:
>> +        return g(&x, &y);
>> +    }
>> +}
>> +
>> +int g1(int, int);
>> +int f1()
>> +{
>> +    switch (0) {
>> +        int x; /* { dg-warning "cannot be initialized with" } */
>> +        int y; /* { dg-warning "cannot be initialized with" } */
>> +        default:
>> +        return g1(x, y);
>> +    }
>> +}
>> +
>> +struct S
>> +{
>> +  char a;
>> +  int b;
>> +};
>> +int g2(int);
>> +int f2(int input)
>> +{
>> +    switch (0) {
>> +        struct S x; /* { dg-warning "cannot be initialized with" } */
>> +        struct S y; /* { dg-warning "cannot be initialized with" } */
>> +        default:
>> +        return g2(input) + x.b + y.b;
>> +    }
>> +}
>> 
> 
> -- 
> Richard Biener <rguenther@suse.de>
> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
  

On Thu, 24 Feb 2022, Qing Zhao wrote:

> 
> 
> > On Feb 24, 2022, at 4:16 AM, Richard Biener <rguenther@suse.de> wrote:
> > 
> > On Sat, 19 Feb 2022, Qing Zhao wrote:
> > 
> >> Hi,
> >> 
> >> This is the 2nd patch for fixing pr102276.
> >> 
> >> Adding -Wtrivial-auto-var-init and update documentation.
> >> 
> >> Adding a new warning option -Wtrivial-auto-var-init to report cases when
> >> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
> >> time, update documentation for -ftrivial-auto-var-init to connect it with
> >> the new warning option -Wtrivial-auto-var-init,  and add documentation
> >> for -Wtrivial-auto-var-init.
> >> 
> >> Bootstraped and regression tested on both x86 and aarch64.
> >> 
> >> Okay for committing?
> >> 
> >> thanks.
> >> 
> >> Qing.
> >> 
> >> ==============================
> >> From 4346890b8f4258489c4841f1992ba3ce816d7689 Mon Sep 17 00:00:00 2001
> >> From: Qing Zhao <qing.zhao@oracle.com>
> >> Date: Fri, 18 Feb 2022 15:53:15 +0000
> >> Subject: [PATCH 2/2] Adding -Wtrivial-auto-var-init and update documentation.
> >> 
> >> Adding a new warning option -Wtrivial-auto-var-init to report cases when
> >> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
> >> time, update documentation for -ftrivial-auto-var-init to connect it with
> >> the new warning option -Wtrivial-auto-var-init,  and add documentation
> >> for -Wtrivial-auto-var-init.
> >> 
> >> 2022-02-18 Qing Zhao  <qing.zhao@oracle.com>
> >> gcc/ChangeLog:
> >> 
> >> 	* common.opt (-Wtrivial-auto-var-init): New option.
> >> 	* doc/invoke.texi (-Wtrivial-auto-var-init): Document new option.
> >> 	(-ftrivial-auto-var-init): Update option;
> >> 	* gimplify.cc (maybe_warn_switch_unreachable): Rename...
> >> 	(maybe_warn_switch_unreachable_and_auto_init): ...to this.
> >> 	(gimplify_switch_expr): Call new function.
> >> 
> >> gcc/testsuite/ChangeLog:
> >> 
> >> 	* gcc.dg/auto-init-pr102276-3.c: New test.
> >> 	* gcc.dg/auto-init-pr102276-4.c: New test.
> >> ---
> >> gcc/common.opt                              |   4 +
> >> gcc/doc/invoke.texi                         |  14 ++-
> >> gcc/gimplify.cc                             | 100 +++++++++++++++-----
> >> gcc/testsuite/gcc.dg/auto-init-pr102276-3.c |  40 ++++++++
> >> gcc/testsuite/gcc.dg/auto-init-pr102276-4.c |  40 ++++++++
> >> 5 files changed, 175 insertions(+), 23 deletions(-)
> >> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
> >> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
> >> 
> >> diff --git a/gcc/common.opt b/gcc/common.opt
> >> index c21e5273ae3..22c95dbfa49 100644
> >> --- a/gcc/common.opt
> >> +++ b/gcc/common.opt
> >> @@ -801,6 +801,10 @@ Wtrampolines
> >> Common Var(warn_trampolines) Warning
> >> Warn whenever a trampoline is generated.
> >> 
> >> +Wtrivial-auto-var-init
> >> +Common Var(warn_trivial_auto_var_init) Warning Init(0)
> >> +Warn about where -ftrivial-auto-var-init cannot initialize the auto variable.
> >> +
> > 
> > Warn about cases where ... initialize a variable.
> 
> Okay. 
> 
> > 
> >> Wtype-limits
> >> Common Var(warn_type_limits) Warning EnabledBy(Wextra)
> >> Warn if a comparison is always true or always false due to the limited range of the data type.
> >> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> >> index e1a00c80307..c61a5b4b4a5 100644
> >> --- a/gcc/doc/invoke.texi
> >> +++ b/gcc/doc/invoke.texi
> >> @@ -399,7 +399,7 @@ Objective-C and Objective-C++ Dialects}.
> >> -Wswitch  -Wno-switch-bool  -Wswitch-default  -Wswitch-enum @gol
> >> -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand @gol
> >> -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
> >> --Wtsan -Wtype-limits  -Wundef @gol
> >> +-Wtrivial-auto-var-init -Wtsan -Wtype-limits  -Wundef @gol
> >> -Wuninitialized  -Wunknown-pragmas @gol
> >> -Wunsuffixed-float-constants  -Wunused @gol
> >> -Wunused-but-set-parameter  -Wunused-but-set-variable @gol
> >> @@ -6953,6 +6953,14 @@ This warning is enabled by default for C and C++ programs.
> >> Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
> >> built-in functions are used.  These functions changed semantics in GCC 4.4.
> >> 
> >> +@item -Wtrivial-auto-var-init
> >> +@opindex Wtrivial-auto-var-init
> >> +@opindex Wno-trivial-auto-var-init
> >> +Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic
> >> +variable.  A common situation is an automatic variable that is declared
> >> +between the controlling expression and the first case lable of a @code{switch}
> >> +statement.
> >> +
> >> @item -Wunused-but-set-parameter
> >> @opindex Wunused-but-set-parameter
> >> @opindex Wno-unused-but-set-parameter
> >> @@ -12314,6 +12322,10 @@ initializer as uninitialized, @option{-Wuninitialized} and
> >> warning messages on such automatic variables.
> >> With this option, GCC will also initialize any padding of automatic variables
> >> that have structure or union types to zeroes.
> >> +However, the current implementation cannot initialize automatic variables that
> >> +are declared between the controlling expression and the first case of a
> >> +@code{switch} statement.  Using @option{-Wtrivial-auto-var-init} to report all
> >> +such cases.
> >> 
> >> The three values of @var{choice} are:
> >> 
> >> diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
> >> index 4e3bbf5314d..7e52794691f 100644
> >> --- a/gcc/gimplify.cc
> >> +++ b/gcc/gimplify.cc
> >> @@ -2079,13 +2079,59 @@ warn_switch_unreachable_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
> >>   return NULL_TREE;
> >> }
> >> 
> >> +/* Callback for walk_gimple_seq.  */
> >> +
> >> +static tree
> >> +warn_switch_unreachable_auto_init_r (gimple_stmt_iterator *gsi_p,
> >> +				     bool *handled_ops_p,
> >> +				     struct walk_stmt_info *)
> >> +{
> >> +  gimple *stmt = gsi_stmt (*gsi_p);
> >> +
> >> +  *handled_ops_p = true;
> >> +  switch (gimple_code (stmt))
> >> +    {
> >> +    case GIMPLE_TRY:
> >> +    case GIMPLE_BIND:
> >> +    case GIMPLE_CATCH:
> >> +    case GIMPLE_EH_FILTER:
> >> +    case GIMPLE_TRANSACTION:
> >> +      /* Walk the sub-statements.  */
> >> +      *handled_ops_p = false;
> >> +      break;
> >> +    case GIMPLE_CALL:
> >> +      if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)
> >> +	  && flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> >> +	{
> >> +	  /* Get the variable name from the 3rd argument of call.  */
> >> +	  tree var_name = gimple_call_arg (stmt, 2);
> >> +	  var_name = TREE_OPERAND (TREE_OPERAND (var_name, 0), 0);
> >> +	  const char *var_name_str = TREE_STRING_POINTER (var_name);
> >> +
> >> +	  warning_at (gimple_location (stmt), OPT_Wtrivial_auto_var_init,
> >> +		      "%qs cannot be initialized with"
> >> +		      "%<-ftrivial-auto-var_init%>",
> >> +		      var_name_str);
> >> +	}
> >> +      break;
> >> +    case GIMPLE_LABEL:
> >> +      /* Stop till the first Label.  */
> >> +      return integer_zero_node;
> >> +    default:
> >> +      break;
> >> +    }
> >> +  return NULL_TREE;
> >> +}
> >> +
> >> /* Possibly warn about unreachable statements between switch's controlling
> >> -   expression and the first case.  SEQ is the body of a switch expression.  */
> >> +   expression and the first case.  Also warn about -ftrivial-auto-var-init
> >> +   cannot initialize the auto variable under such situation.
> >> +   SEQ is the body of a switch expression.  */
> >> 
> >> static void
> >> -maybe_warn_switch_unreachable (gimple_seq seq)
> >> +maybe_warn_switch_unreachable_and_auto_init (gimple_seq seq)
> >> {
> >> -  if (!warn_switch_unreachable
> >> +  if ((!warn_switch_unreachable && !warn_trivial_auto_var_init)
> >>       /* This warning doesn't play well with Fortran when optimizations
> >> 	 are on.  */
> >>       || lang_GNU_Fortran ()
> >> @@ -2093,26 +2139,36 @@ maybe_warn_switch_unreachable (gimple_seq seq)
> >>     return;
> >> 
> >>   struct walk_stmt_info wi;
> >> -  memset (&wi, 0, sizeof (wi));
> >> -  walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
> >> -  gimple *stmt = (gimple *) wi.info;
> >> 
> >> -  if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
> >> +  if (warn_switch_unreachable)
> >>     {
> >> -      if (gimple_code (stmt) == GIMPLE_GOTO
> >> -	  && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
> >> -	  && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
> >> -	/* Don't warn for compiler-generated gotos.  These occur
> >> -	   in Duff's devices, for example.  */
> >> -	;
> >> -      else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> >> -		&& (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
> >> -	/* Don't warn for compiler-generated initializations for
> >> -	  -ftrivial-auto-var-init.  */
> >> -	;
> >> -      else
> >> -	warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
> >> -		    "statement will never be executed");
> >> +      memset (&wi, 0, sizeof (wi));
> >> +      walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
> >> +      gimple *stmt = (gimple *) wi.info;
> >> +
> >> +      if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
> >> +	{
> >> +	  if (gimple_code (stmt) == GIMPLE_GOTO
> >> +	      && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
> >> +	      && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
> >> +	  /* Don't warn for compiler-generated gotos.  These occur
> >> +	     in Duff's devices, for example.  */
> >> +	    ;
> >> +	  else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> >> +		   && (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
> >> +	  /* Don't warn for compiler-generated initializations for
> >> +	     -ftrivial-auto-var-init.  */
> >> +	    ;
> >> +	  else
> >> +	    warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
> >> +			"statement will never be executed");
> >> +	}
> >> +    }
> > 
> > Hmm.  I'd re-organize the code to emit both the Wswitch-unreachable 
> > and -Wtrivial_auto_var_init diagnostic from the existing
> > warn_switch_unreachable_r callback.  You can use wi.info to keep
> > track whether a Wswitch-unreachable diagnostic was already emitted
> > (and if -Wtrivial_auto_var_init is not enabled abort the walk)
> > for example.
> 
> Okay. Will try this.
> 
> A question here: for the current -Wswitch-unreachable, the warning will be emit only once for the first unreachable stmt. 
> Shall we emit warning for each unreachable stmt instead?

No, only for the first one.  But we might want to diagnose all
not auto-init variables.

Richard.

> thanks.
> 
> Qing
> > 
> > Thanks,
> > Richard.
> > 
> >> +  if (warn_trivial_auto_var_init)
> >> +    {
> >> +      memset (&wi, 0, sizeof (wi));
> >> +      walk_gimple_seq (seq, warn_switch_unreachable_auto_init_r, NULL, &wi);
> >>     }
> >> }
> >> 
> >> @@ -2646,7 +2702,7 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
> >>       gimplify_stmt (&SWITCH_BODY (switch_expr), &switch_body_seq);
> >> 
> >>       gimplify_ctxp->in_switch_expr = old_in_switch_expr;
> >> -      maybe_warn_switch_unreachable (switch_body_seq);
> >> +      maybe_warn_switch_unreachable_and_auto_init (switch_body_seq);
> >>       maybe_warn_implicit_fallthrough (switch_body_seq);
> >>       /* Only do this for the outermost GIMPLE_SWITCH.  */
> >>       if (!gimplify_ctxp->in_switch_expr)
> >> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
> >> new file mode 100644
> >> index 00000000000..f113f46e29d
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
> >> @@ -0,0 +1,40 @@
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=zero" } */
> >> +
> >> +int g(int *, int *);
> >> +int f()
> >> +{
> >> +    switch (0) {
> >> +        int x;  /* { dg-warning "cannot be initialized with" } */
> >> +        int y;  /* { dg-warning "cannot be initialized with" } */
> >> +        default:
> >> +        return g(&x, &y);
> >> +    }
> >> +}
> >> +
> >> +int g1(int, int);
> >> +int f1()
> >> +{
> >> +    switch (0) {
> >> +        int x; /* { dg-warning "cannot be initialized with" } */
> >> +        int y; /* { dg-warning "cannot be initialized with" } */
> >> +        default:
> >> +        return g1(x, y);
> >> +    }
> >> +}
> >> +
> >> +struct S
> >> +{
> >> +  char a;
> >> +  int b;
> >> +};
> >> +int g2(int);
> >> +int f2(int input)
> >> +{
> >> +    switch (0) {
> >> +        struct S x; /* { dg-warning "cannot be initialized with" } */
> >> +        struct S y; /* { dg-warning "cannot be initialized with" } */
> >> +        default:
> >> +        return g2(input) + x.b + y.b;
> >> +    }
> >> +}
> >> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
> >> new file mode 100644
> >> index 00000000000..662e0d1182e
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
> >> @@ -0,0 +1,40 @@
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=pattern" } */
> >> +
> >> +int g(int *, int *);
> >> +int f()
> >> +{
> >> +    switch (0) {
> >> +        int x;  /* { dg-warning "cannot be initialized with" } */
> >> +        int y;  /* { dg-warning "cannot be initialized with" } */
> >> +        default:
> >> +        return g(&x, &y);
> >> +    }
> >> +}
> >> +
> >> +int g1(int, int);
> >> +int f1()
> >> +{
> >> +    switch (0) {
> >> +        int x; /* { dg-warning "cannot be initialized with" } */
> >> +        int y; /* { dg-warning "cannot be initialized with" } */
> >> +        default:
> >> +        return g1(x, y);
> >> +    }
> >> +}
> >> +
> >> +struct S
> >> +{
> >> +  char a;
> >> +  int b;
> >> +};
> >> +int g2(int);
> >> +int f2(int input)
> >> +{
> >> +    switch (0) {
> >> +        struct S x; /* { dg-warning "cannot be initialized with" } */
> >> +        struct S y; /* { dg-warning "cannot be initialized with" } */
> >> +        default:
> >> +        return g2(input) + x.b + y.b;
> >> +    }
> >> +}
> >> 
> > 
> > -- 
> > Richard Biener <rguenther@suse.de>
> > SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> > Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
> 
>
  

> On Feb 25, 2022, at 6:43 AM, Richard Biener <rguenther@suse.de> wrote:
> 
> On Thu, 24 Feb 2022, Qing Zhao wrote:
> 
>> 
>> 
>>> On Feb 24, 2022, at 4:16 AM, Richard Biener <rguenther@suse.de> wrote:
>>> 
>>> On Sat, 19 Feb 2022, Qing Zhao wrote:
>>> 
>>>> Hi,
>>>> 
>>>> This is the 2nd patch for fixing pr102276.
>>>> 
>>>> Adding -Wtrivial-auto-var-init and update documentation.
>>>> 
>>>> Adding a new warning option -Wtrivial-auto-var-init to report cases when
>>>> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
>>>> time, update documentation for -ftrivial-auto-var-init to connect it with
>>>> the new warning option -Wtrivial-auto-var-init,  and add documentation
>>>> for -Wtrivial-auto-var-init.
>>>> 
>>>> Bootstraped and regression tested on both x86 and aarch64.
>>>> 
>>>> Okay for committing?
>>>> 
>>>> thanks.
>>>> 
>>>> Qing.
>>>> 
>>>> ==============================
>>>> From 4346890b8f4258489c4841f1992ba3ce816d7689 Mon Sep 17 00:00:00 2001
>>>> From: Qing Zhao <qing.zhao@oracle.com>
>>>> Date: Fri, 18 Feb 2022 15:53:15 +0000
>>>> Subject: [PATCH 2/2] Adding -Wtrivial-auto-var-init and update documentation.
>>>> 
>>>> Adding a new warning option -Wtrivial-auto-var-init to report cases when
>>>> -ftrivial-auto-var-init cannot initialize the auto variable. At the same
>>>> time, update documentation for -ftrivial-auto-var-init to connect it with
>>>> the new warning option -Wtrivial-auto-var-init,  and add documentation
>>>> for -Wtrivial-auto-var-init.
>>>> 
>>>> 2022-02-18 Qing Zhao  <qing.zhao@oracle.com>
>>>> gcc/ChangeLog:
>>>> 
>>>> 	* common.opt (-Wtrivial-auto-var-init): New option.
>>>> 	* doc/invoke.texi (-Wtrivial-auto-var-init): Document new option.
>>>> 	(-ftrivial-auto-var-init): Update option;
>>>> 	* gimplify.cc (maybe_warn_switch_unreachable): Rename...
>>>> 	(maybe_warn_switch_unreachable_and_auto_init): ...to this.
>>>> 	(gimplify_switch_expr): Call new function.
>>>> 
>>>> gcc/testsuite/ChangeLog:
>>>> 
>>>> 	* gcc.dg/auto-init-pr102276-3.c: New test.
>>>> 	* gcc.dg/auto-init-pr102276-4.c: New test.
>>>> ---
>>>> gcc/common.opt                              |   4 +
>>>> gcc/doc/invoke.texi                         |  14 ++-
>>>> gcc/gimplify.cc                             | 100 +++++++++++++++-----
>>>> gcc/testsuite/gcc.dg/auto-init-pr102276-3.c |  40 ++++++++
>>>> gcc/testsuite/gcc.dg/auto-init-pr102276-4.c |  40 ++++++++
>>>> 5 files changed, 175 insertions(+), 23 deletions(-)
>>>> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>>>> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
>>>> 
>>>> diff --git a/gcc/common.opt b/gcc/common.opt
>>>> index c21e5273ae3..22c95dbfa49 100644
>>>> --- a/gcc/common.opt
>>>> +++ b/gcc/common.opt
>>>> @@ -801,6 +801,10 @@ Wtrampolines
>>>> Common Var(warn_trampolines) Warning
>>>> Warn whenever a trampoline is generated.
>>>> 
>>>> +Wtrivial-auto-var-init
>>>> +Common Var(warn_trivial_auto_var_init) Warning Init(0)
>>>> +Warn about where -ftrivial-auto-var-init cannot initialize the auto variable.
>>>> +
>>> 
>>> Warn about cases where ... initialize a variable.
>> 
>> Okay. 
>> 
>>> 
>>>> Wtype-limits
>>>> Common Var(warn_type_limits) Warning EnabledBy(Wextra)
>>>> Warn if a comparison is always true or always false due to the limited range of the data type.
>>>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>>>> index e1a00c80307..c61a5b4b4a5 100644
>>>> --- a/gcc/doc/invoke.texi
>>>> +++ b/gcc/doc/invoke.texi
>>>> @@ -399,7 +399,7 @@ Objective-C and Objective-C++ Dialects}.
>>>> -Wswitch  -Wno-switch-bool  -Wswitch-default  -Wswitch-enum @gol
>>>> -Wno-switch-outside-range  -Wno-switch-unreachable  -Wsync-nand @gol
>>>> -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
>>>> --Wtsan -Wtype-limits  -Wundef @gol
>>>> +-Wtrivial-auto-var-init -Wtsan -Wtype-limits  -Wundef @gol
>>>> -Wuninitialized  -Wunknown-pragmas @gol
>>>> -Wunsuffixed-float-constants  -Wunused @gol
>>>> -Wunused-but-set-parameter  -Wunused-but-set-variable @gol
>>>> @@ -6953,6 +6953,14 @@ This warning is enabled by default for C and C++ programs.
>>>> Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
>>>> built-in functions are used.  These functions changed semantics in GCC 4.4.
>>>> 
>>>> +@item -Wtrivial-auto-var-init
>>>> +@opindex Wtrivial-auto-var-init
>>>> +@opindex Wno-trivial-auto-var-init
>>>> +Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic
>>>> +variable.  A common situation is an automatic variable that is declared
>>>> +between the controlling expression and the first case lable of a @code{switch}
>>>> +statement.
>>>> +
>>>> @item -Wunused-but-set-parameter
>>>> @opindex Wunused-but-set-parameter
>>>> @opindex Wno-unused-but-set-parameter
>>>> @@ -12314,6 +12322,10 @@ initializer as uninitialized, @option{-Wuninitialized} and
>>>> warning messages on such automatic variables.
>>>> With this option, GCC will also initialize any padding of automatic variables
>>>> that have structure or union types to zeroes.
>>>> +However, the current implementation cannot initialize automatic variables that
>>>> +are declared between the controlling expression and the first case of a
>>>> +@code{switch} statement.  Using @option{-Wtrivial-auto-var-init} to report all
>>>> +such cases.
>>>> 
>>>> The three values of @var{choice} are:
>>>> 
>>>> diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
>>>> index 4e3bbf5314d..7e52794691f 100644
>>>> --- a/gcc/gimplify.cc
>>>> +++ b/gcc/gimplify.cc
>>>> @@ -2079,13 +2079,59 @@ warn_switch_unreachable_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
>>>>  return NULL_TREE;
>>>> }
>>>> 
>>>> +/* Callback for walk_gimple_seq.  */
>>>> +
>>>> +static tree
>>>> +warn_switch_unreachable_auto_init_r (gimple_stmt_iterator *gsi_p,
>>>> +				     bool *handled_ops_p,
>>>> +				     struct walk_stmt_info *)
>>>> +{
>>>> +  gimple *stmt = gsi_stmt (*gsi_p);
>>>> +
>>>> +  *handled_ops_p = true;
>>>> +  switch (gimple_code (stmt))
>>>> +    {
>>>> +    case GIMPLE_TRY:
>>>> +    case GIMPLE_BIND:
>>>> +    case GIMPLE_CATCH:
>>>> +    case GIMPLE_EH_FILTER:
>>>> +    case GIMPLE_TRANSACTION:
>>>> +      /* Walk the sub-statements.  */
>>>> +      *handled_ops_p = false;
>>>> +      break;
>>>> +    case GIMPLE_CALL:
>>>> +      if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)
>>>> +	  && flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
>>>> +	{
>>>> +	  /* Get the variable name from the 3rd argument of call.  */
>>>> +	  tree var_name = gimple_call_arg (stmt, 2);
>>>> +	  var_name = TREE_OPERAND (TREE_OPERAND (var_name, 0), 0);
>>>> +	  const char *var_name_str = TREE_STRING_POINTER (var_name);
>>>> +
>>>> +	  warning_at (gimple_location (stmt), OPT_Wtrivial_auto_var_init,
>>>> +		      "%qs cannot be initialized with"
>>>> +		      "%<-ftrivial-auto-var_init%>",
>>>> +		      var_name_str);
>>>> +	}
>>>> +      break;
>>>> +    case GIMPLE_LABEL:
>>>> +      /* Stop till the first Label.  */
>>>> +      return integer_zero_node;
>>>> +    default:
>>>> +      break;
>>>> +    }
>>>> +  return NULL_TREE;
>>>> +}
>>>> +
>>>> /* Possibly warn about unreachable statements between switch's controlling
>>>> -   expression and the first case.  SEQ is the body of a switch expression.  */
>>>> +   expression and the first case.  Also warn about -ftrivial-auto-var-init
>>>> +   cannot initialize the auto variable under such situation.
>>>> +   SEQ is the body of a switch expression.  */
>>>> 
>>>> static void
>>>> -maybe_warn_switch_unreachable (gimple_seq seq)
>>>> +maybe_warn_switch_unreachable_and_auto_init (gimple_seq seq)
>>>> {
>>>> -  if (!warn_switch_unreachable
>>>> +  if ((!warn_switch_unreachable && !warn_trivial_auto_var_init)
>>>>      /* This warning doesn't play well with Fortran when optimizations
>>>> 	 are on.  */
>>>>      || lang_GNU_Fortran ()
>>>> @@ -2093,26 +2139,36 @@ maybe_warn_switch_unreachable (gimple_seq seq)
>>>>    return;
>>>> 
>>>>  struct walk_stmt_info wi;
>>>> -  memset (&wi, 0, sizeof (wi));
>>>> -  walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
>>>> -  gimple *stmt = (gimple *) wi.info;
>>>> 
>>>> -  if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
>>>> +  if (warn_switch_unreachable)
>>>>    {
>>>> -      if (gimple_code (stmt) == GIMPLE_GOTO
>>>> -	  && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
>>>> -	  && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
>>>> -	/* Don't warn for compiler-generated gotos.  These occur
>>>> -	   in Duff's devices, for example.  */
>>>> -	;
>>>> -      else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
>>>> -		&& (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
>>>> -	/* Don't warn for compiler-generated initializations for
>>>> -	  -ftrivial-auto-var-init.  */
>>>> -	;
>>>> -      else
>>>> -	warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
>>>> -		    "statement will never be executed");
>>>> +      memset (&wi, 0, sizeof (wi));
>>>> +      walk_gimple_seq (seq, warn_switch_unreachable_r, NULL, &wi);
>>>> +      gimple *stmt = (gimple *) wi.info;
>>>> +
>>>> +      if (stmt && gimple_code (stmt) != GIMPLE_LABEL)
>>>> +	{
>>>> +	  if (gimple_code (stmt) == GIMPLE_GOTO
>>>> +	      && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
>>>> +	      && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
>>>> +	  /* Don't warn for compiler-generated gotos.  These occur
>>>> +	     in Duff's devices, for example.  */
>>>> +	    ;
>>>> +	  else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
>>>> +		   && (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)))
>>>> +	  /* Don't warn for compiler-generated initializations for
>>>> +	     -ftrivial-auto-var-init.  */
>>>> +	    ;
>>>> +	  else
>>>> +	    warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
>>>> +			"statement will never be executed");
>>>> +	}
>>>> +    }
>>> 
>>> Hmm.  I'd re-organize the code to emit both the Wswitch-unreachable 
>>> and -Wtrivial_auto_var_init diagnostic from the existing
>>> warn_switch_unreachable_r callback.  You can use wi.info to keep
>>> track whether a Wswitch-unreachable diagnostic was already emitted
>>> (and if -Wtrivial_auto_var_init is not enabled abort the walk)
>>> for example.
>> 
>> Okay. Will try this.
>> 
>> A question here: for the current -Wswitch-unreachable, the warning will be emit only once for the first unreachable stmt. 
>> Shall we emit warning for each unreachable stmt instead?
> 
> No, only for the first one.  But we might want to diagnose all
> not auto-init variables.

Okay.

Qing
> 
> Richard.
> 
>> thanks.
>> 
>> Qing
>>> 
>>> Thanks,
>>> Richard.
>>> 
>>>> +  if (warn_trivial_auto_var_init)
>>>> +    {
>>>> +      memset (&wi, 0, sizeof (wi));
>>>> +      walk_gimple_seq (seq, warn_switch_unreachable_auto_init_r, NULL, &wi);
>>>>    }
>>>> }
>>>> 
>>>> @@ -2646,7 +2702,7 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
>>>>      gimplify_stmt (&SWITCH_BODY (switch_expr), &switch_body_seq);
>>>> 
>>>>      gimplify_ctxp->in_switch_expr = old_in_switch_expr;
>>>> -      maybe_warn_switch_unreachable (switch_body_seq);
>>>> +      maybe_warn_switch_unreachable_and_auto_init (switch_body_seq);
>>>>      maybe_warn_implicit_fallthrough (switch_body_seq);
>>>>      /* Only do this for the outermost GIMPLE_SWITCH.  */
>>>>      if (!gimplify_ctxp->in_switch_expr)
>>>> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>>>> new file mode 100644
>>>> index 00000000000..f113f46e29d
>>>> --- /dev/null
>>>> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-3.c
>>>> @@ -0,0 +1,40 @@
>>>> +/* { dg-do compile } */
>>>> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=zero" } */
>>>> +
>>>> +int g(int *, int *);
>>>> +int f()
>>>> +{
>>>> +    switch (0) {
>>>> +        int x;  /* { dg-warning "cannot be initialized with" } */
>>>> +        int y;  /* { dg-warning "cannot be initialized with" } */
>>>> +        default:
>>>> +        return g(&x, &y);
>>>> +    }
>>>> +}
>>>> +
>>>> +int g1(int, int);
>>>> +int f1()
>>>> +{
>>>> +    switch (0) {
>>>> +        int x; /* { dg-warning "cannot be initialized with" } */
>>>> +        int y; /* { dg-warning "cannot be initialized with" } */
>>>> +        default:
>>>> +        return g1(x, y);
>>>> +    }
>>>> +}
>>>> +
>>>> +struct S
>>>> +{
>>>> +  char a;
>>>> +  int b;
>>>> +};
>>>> +int g2(int);
>>>> +int f2(int input)
>>>> +{
>>>> +    switch (0) {
>>>> +        struct S x; /* { dg-warning "cannot be initialized with" } */
>>>> +        struct S y; /* { dg-warning "cannot be initialized with" } */
>>>> +        default:
>>>> +        return g2(input) + x.b + y.b;
>>>> +    }
>>>> +}
>>>> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
>>>> new file mode 100644
>>>> index 00000000000..662e0d1182e
>>>> --- /dev/null
>>>> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-4.c
>>>> @@ -0,0 +1,40 @@
>>>> +/* { dg-do compile } */
>>>> +/* { dg-options "-O2 -Wtrivial-auto-var-init -ftrivial-auto-var-init=pattern" } */
>>>> +
>>>> +int g(int *, int *);
>>>> +int f()
>>>> +{
>>>> +    switch (0) {
>>>> +        int x;  /* { dg-warning "cannot be initialized with" } */
>>>> +        int y;  /* { dg-warning "cannot be initialized with" } */
>>>> +        default:
>>>> +        return g(&x, &y);
>>>> +    }
>>>> +}
>>>> +
>>>> +int g1(int, int);
>>>> +int f1()
>>>> +{
>>>> +    switch (0) {
>>>> +        int x; /* { dg-warning "cannot be initialized with" } */
>>>> +        int y; /* { dg-warning "cannot be initialized with" } */
>>>> +        default:
>>>> +        return g1(x, y);
>>>> +    }
>>>> +}
>>>> +
>>>> +struct S
>>>> +{
>>>> +  char a;
>>>> +  int b;
>>>> +};
>>>> +int g2(int);
>>>> +int f2(int input)
>>>> +{
>>>> +    switch (0) {
>>>> +        struct S x; /* { dg-warning "cannot be initialized with" } */
>>>> +        struct S y; /* { dg-warning "cannot be initialized with" } */
>>>> +        default:
>>>> +        return g2(input) + x.b + y.b;
>>>> +    }
>>>> +}
>>>> 
>>> 
>>> -- 
>>> Richard Biener <rguenther@suse.de>
>>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
>>> Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
>> 
>> 
> 
> -- 
> Richard Biener <rguenther@suse.de>
> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)