On Tue, 1 Mar 2022, Qing Zhao wrote:
> Hi,
>
> This is the 2nd version of the patch based on the discussion on the initial
> version.
>
> Compared to the previous version, the major changes in this version are:
>
> 1. Merged two patches into one;
> 2. Re-organize the code to emit both Wswitch-unreachable and
> Wtrivial-auto-var-init
> Messages inside existing “warn_switch_unreachable_r”;
> 3. Avoid emitting Wswitch-unreachable for the following 3 cases:
>
> 1) call to .DEFERRED_INIT
> 2) call to __builtin_clear_padding if the 2nd argument is present and non-zero
> 3) a gimple assign store right after the .DEFERRED_INIT call that has the LHS
> as RHS
>
>
> Bootstraped and regression tested on both x86 and aarch64.
>
> Okay for committing?
OK.
Thanks,
Richard.
> thanks.
>
> Qing.
>
> ========================
> From ca0193f48c8ae11719aa932db065bb24d4d649d7 Mon Sep 17 00:00:00 2001
> From: Qing Zhao <qing.z...@oracle.com>
> Date: Mon, 28 Feb 2022 21:45:55 +0000
> Subject: [PATCH] Don't emit switch-unreachable warnings for
> -ftrivial-auto-var-init (PR102276) At the same time, adding
> -Wtrivial-auto-var-init and update documentation.
>
> for the following testing case:
> 1 int g(int *);
> 2 int f1()
> 3 {
> 4 switch (0) {
> 5 int x;
> 6 default:
> 7 return g(&x);
> 8 }
> 9 }
> compiling with -O -ftrivial-auto-var-init causes spurious warning:
> warning: statement will never be executed [-Wswitch-unreachable]
> 5 | int x;
> | ^
> This is due to the compiler-generated initialization at the point of
> the declaration.
>
> We could avoid the warning to exclude the following cases:
>
> when
> flag_auto_var_init > AUTO_INIT_UNINITIALIZED
> And
> 1) call to .DEFERRED_INIT
> 2) call to __builtin_clear_padding if the 2nd argument is present and non-zero
> 3) a gimple assign store right after the .DEFERRED_INIT call that has the LHS
> as RHS
>
> However, we still need to warn users about the incapability of the option
> -ftrivial-auto-var-init by adding a new warning option -Wtrivial-auto-var-init
> to report cases when it 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.
>
> 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 (emit_warn_switch_unreachable): New function.
> (warn_switch_unreachable_r): Rename to ...
> (warn_switch_unreachable_and_auto_init_r): This.
> (maybe_warn_switch_unreachable): Rename to ...
> (maybe_warn_switch_unreachable_and_auto_init): This.
> (gimplify_switch_expr): Update calls to renamed function.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/auto-init-pr102276-1.c: New test.
> * gcc.dg/auto-init-pr102276-2.c: New test.
> * 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 | 111 +++++++++++++++-----
> gcc/testsuite/gcc.dg/auto-init-pr102276-1.c | 38 +++++++
> gcc/testsuite/gcc.dg/auto-init-pr102276-2.c | 38 +++++++
> gcc/testsuite/gcc.dg/auto-init-pr102276-3.c | 40 +++++++
> gcc/testsuite/gcc.dg/auto-init-pr102276-4.c | 40 +++++++
> 7 files changed, 259 insertions(+), 26 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-1.c
> create mode 100644 gcc/testsuite/gcc.dg/auto-init-pr102276-2.c
> 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..8b6513de47c 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 cases where -ftrivial-auto-var-init cannot initialize an auto
> 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 ec291c06542..63a3c5b7c7e 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 label 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 f570daa015a..2364d2e5182 100644
> --- a/gcc/gimplify.cc
> +++ b/gcc/gimplify.cc
> @@ -2029,13 +2029,55 @@ gimplify_statement_list (tree *expr_p, gimple_seq
> *pre_p)
> return GS_ALL_DONE;
> }
>
> +
> +/* Emit warning for the unreachable statment STMT if needed.
> + Return the gimple itself when the warning is emitted, otherwise
> + return NULL. */
> +static gimple *
> +emit_warn_switch_unreachable (gimple *stmt)
> +{
> + 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. */
> + return NULL;
> + else if ((flag_auto_var_init > AUTO_INIT_UNINITIALIZED)
> + && ((gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
> + || (gimple_call_builtin_p (stmt, BUILT_IN_CLEAR_PADDING)
> + && (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 1)))
> + || (is_gimple_assign (stmt)
> + && gimple_assign_single_p (stmt)
> + && (TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME)
> + && gimple_call_internal_p (
> + SSA_NAME_DEF_STMT (gimple_assign_rhs1 (stmt)),
> + IFN_DEFERRED_INIT))))
> + /* Don't warn for compiler-generated initializations for
> + -ftrivial-auto-var-init.
> + There are 3 cases:
> + case 1: a call to .DEFERRED_INIT;
> + case 2: a call to __builtin_clear_padding with the 2nd argument is
> + present and non-zero;
> + case 3: a gimple assign store right after the call to .DEFERRED_INIT
> + that has the LHS of .DEFERRED_INIT as the RHS as following:
> + _1 = .DEFERRED_INIT (4, 2, &"i1"[0]);
> + i1 = _1. */
> + return NULL;
> + else
> + warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
> + "statement will never be executed");
> + return stmt;
> +}
> +
> /* Callback for walk_gimple_seq. */
>
> static tree
> -warn_switch_unreachable_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
> - struct walk_stmt_info *wi)
> +warn_switch_unreachable_and_auto_init_r (gimple_stmt_iterator *gsi_p,
> + bool *handled_ops_p,
> + struct walk_stmt_info *wi)
> {
> gimple *stmt = gsi_stmt (*gsi_p);
> + bool unreachable_issued = wi->info != NULL;
>
> *handled_ops_p = true;
> switch (gimple_code (stmt))
> @@ -2046,8 +2088,12 @@ warn_switch_unreachable_r (gimple_stmt_iterator
> *gsi_p, bool *handled_ops_p,
> worse location info. */
> if (gimple_try_eval (stmt) == NULL)
> {
> - wi->info = stmt;
> - return integer_zero_node;
> + if (warn_switch_unreachable && !unreachable_issued)
> + wi->info = emit_warn_switch_unreachable (stmt);
> +
> + /* Stop when auto var init warning is not on. */
> + if (!warn_trivial_auto_var_init)
> + return integer_zero_node;
> }
> /* Fall through. */
> case GIMPLE_BIND:
> @@ -2064,28 +2110,55 @@ warn_switch_unreachable_r (gimple_stmt_iterator
> *gsi_p, bool *handled_ops_p,
> there will be non-debug stmts too, and we'll catch those. */
> break;
>
> + case GIMPLE_LABEL:
> + /* Stop till the first Label. */
> + return integer_zero_node;
> case GIMPLE_CALL:
> if (gimple_call_internal_p (stmt, IFN_ASAN_MARK))
> {
> *handled_ops_p = false;
> break;
> }
> + if (warn_trivial_auto_var_init
> + && flag_auto_var_init > AUTO_INIT_UNINITIALIZED
> + && gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
> + {
> + /* 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;
> + }
> +
> /* Fall through. */
> default:
> - /* Save the first "real" statement (not a decl/lexical scope/...). */
> - wi->info = stmt;
> - return integer_zero_node;
> + /* check the first "real" statement (not a decl/lexical scope/...),
> issue
> + warning if needed. */
> + if (warn_switch_unreachable && !unreachable_issued)
> + wi->info = emit_warn_switch_unreachable (stmt);
> + /* Stop when auto var init warning is not on. */
> + if (!warn_trivial_auto_var_init)
> + return integer_zero_node;
> + 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 ()
> @@ -2093,21 +2166,9 @@ 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 (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
> - 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_and_auto_init_r, NULL, &wi);
> }
>
>
> @@ -2640,7 +2701,7 @@ 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-pr102276-1.c
> b/gcc/testsuite/gcc.dg/auto-init-pr102276-1.c
> new file mode 100644
> index 00000000000..d574926e0c8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-1.c
> @@ -0,0 +1,38 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wall -ftrivial-auto-var-init=zero" } */
> +
> +int g(int *);
> +int f()
> +{
> + switch (0) {
> + int x; /* { dg-bogus "statement will never be executed" } */
> + default:
> + return g(&x);
> + }
> +}
> +
> +int g1(int);
> +int f1()
> +{
> + switch (0) {
> + int x; /* { dg-bogus "statement will never be executed" } */
> + default:
> + return g1(x); /* { dg-warning "is used uninitialized" } */
> + }
> +}
> +
> +struct S
> +{
> + char a;
> + int b;
> +};
> +int g2(int);
> +int f2(int input)
> +{
> + switch (0) {
> + struct S x; /* { dg-bogus "statement will never be executed" } */
> + default:
> + return g2(input) + x.b; /* { dg-warning "is used uninitialized" } */
> + }
> +}
> +
> diff --git a/gcc/testsuite/gcc.dg/auto-init-pr102276-2.c
> b/gcc/testsuite/gcc.dg/auto-init-pr102276-2.c
> new file mode 100644
> index 00000000000..779d3ec3882
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/auto-init-pr102276-2.c
> @@ -0,0 +1,38 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -Wall -ftrivial-auto-var-init=pattern" } */
> +
> +int g(int *);
> +int f()
> +{
> + switch (0) {
> + int x; /* { dg-bogus "statement will never be executed" } */
> + default:
> + return g(&x);
> + }
> +}
> +
> +int g1(int);
> +int f1()
> +{
> + switch (0) {
> + int x; /* { dg-bogus "statement will never be executed" } */
> + default:
> + return g1(x); /* { dg-warning "is used uninitialized" } */
> + }
> +}
> +
> +struct S
> +{
> + char a;
> + int b;
> +};
> +int g2(int);
> +int f2(int input)
> +{
> + switch (0) {
> + struct S x; /* { dg-bogus "statement will never be executed" } */
> + default:
> + return g2(input) + x.b; /* { dg-warning "is used uninitialized" } */
> + }
> +}
> +
> 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 <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
