On Thu, 24 Feb 2022, Qing Zhao wrote:
>
>
> > On Feb 24, 2022, at 4:16 AM, Richard Biener <rguent...@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.z...@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.z...@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 <rguent...@suse.de>
> > SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> > Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
