On December 1, 2017 12:16:55 AM GMT+01:00, Jakub Jelinek <ja...@redhat.com>
wrote:
>Hi!
>
>A nested switch that can fallthrough (either because it has break stmts
>or because it doesn't have default: and doesn't cover all cases) isn't
>unfortunately reported with -Wimplicit-fallthrough, because we first
>gimplify the nested switch and then we just see a label added
>implicitly
>for break; or for the default: case if it was missing and the cases
>don't
>cover all possible values and punt on that.
>
>The following patch fixes it by telling the -Wimplicit-fallthrough
>code about the special labels added for break; or missing default:
>through a new SWITCH_BREAK_LABEL_P flag. Additionally it makes sure
>that GIMPLE_LABEL is emitted still inside of the switch's body sequence
>and if it is a nested switch, it wraps the GIMPLE_SWITCH with the body
>that ends in a GIMPLE_LABEL with SWITCH_BREAK_LABEL_P in a GIMPLE_BIND
>(without vars or blocks). With this, the -Wimplicit-fallthrough code
>can recognize this and treat the whole switch that can fall through as
>a single statement for the purpose of the warning.
>
>Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Richard.
>2017-11-30 Jakub Jelinek <ja...@redhat.com>
>
> PR c/79153
> * tree.h (SWITCH_BREAK_LABEL_P): Define.
> * gimplify.c (collect_fallthrough_labels): Handle GIMPLE_BIND
> starting with a GIMPLE_SWITCH and ending with GIMPLE_LABEL with
> SWITCH_BREAK_LABEL_P set on the label.
> (gimplify_switch_expr): Set SWITCH_BREAK_LABEL_P on the label
> added for default case if it was missing and not all cases covered.
> Wrap GIMPLE_SWITCH and the switch_body_seq into a GIMPLE_BIND if
> switch_body_seq ends with a GIMPLE_LABEL with SWITCH_BREAK_LABEL_P
> set on the label.
> * tree-chrec.c (evolution_function_is_univariate_p): Add return true;
> to avoid -Wimplicit-fallthrough warning.
> * config/i386/i386.c (ix86_expand_special_args_builtin): Add
> FALLTHRU comment to avoid -Wimplicit-fallthrough warning.
>c/
> * c-parser.c: Include tree-iterator.h.
> (c_parser_switch_statement): Emit LABEL_EXPR for the break label
> into SWITCH_BODY instead of after it and set SWITCH_BREAK_LABEL_P
> on it.
>cp/
> * cp-gimplify.c (genericize_switch_stmt): Emit LABEL_EXPR for the
> break label into SWITCH_BODY instead of after it and set
> SWITCH_BREAK_LABEL_P on it.
> * parser.c (cp_parser_objc_expression): Add FALLTHRU comment to avoid
> -Wimplicit-fallthrough warning.
>fortran/
> * match.c (gfc_match): Add FALLTHRU comment to avoid
> -Wimplicit-fallthrough warning.
>testsuite/
> * c-c++-common/Wimplicit-fallthrough-7.c: Adjust expected warning
> line.
> * c-c++-common/Wimplicit-fallthrough-36.c: New test.
>
>--- gcc/tree.h.jj 2017-11-28 22:21:17.000000000 +0100
>+++ gcc/tree.h 2017-11-30 17:55:35.299197618 +0100
>@@ -766,6 +766,11 @@ extern void omp_clause_range_check_faile
> #define FALLTHROUGH_LABEL_P(NODE) \
> (LABEL_DECL_CHECK (NODE)->base.private_flag)
>
>+/* Set on the artificial label created for break; stmt from a switch.
>+ This is used to implement -Wimplicit-fallthrough. */
>+#define SWITCH_BREAK_LABEL_P(NODE) \
>+ (LABEL_DECL_CHECK (NODE)->base.protected_flag)
>+
> /* Nonzero means this expression is volatile in the C sense:
> its address should be of type `volatile WHATEVER *'.
> In other words, the declared item is volatile qualified.
>--- gcc/gimplify.c.jj 2017-11-28 12:11:40.000000000 +0100
>+++ gcc/gimplify.c 2017-11-30 19:04:32.694173903 +0100
>@@ -1897,6 +1897,27 @@ collect_fallthrough_labels (gimple_stmt_
>
> do
> {
>+ if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_BIND)
>+ {
>+ /* Recognize the special GIMPLE_BIND added by gimplify_switch_expr,
>+ which starts on a GIMPLE_SWITCH and ends with a break label.
>+ Handle that as a single statement that can fall through. */
>+ gbind *bind = as_a <gbind *> (gsi_stmt (*gsi_p));
>+ gimple *first = gimple_seq_first_stmt (gimple_bind_body (bind));
>+ gimple *last = gimple_seq_last_stmt (gimple_bind_body (bind));
>+ if (last
>+ && gimple_code (first) == GIMPLE_SWITCH
>+ && gimple_code (last) == GIMPLE_LABEL)
>+ {
>+ tree label = gimple_label_label (as_a <glabel *> (last));
>+ if (SWITCH_BREAK_LABEL_P (label))
>+ {
>+ prev = bind;
>+ gsi_next (gsi_p);
>+ continue;
>+ }
>+ }
>+ }
> if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_BIND
> || gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_TRY)
> {
>@@ -2315,6 +2336,7 @@ gimplify_switch_expr (tree *expr_p, gimp
> preprocess_case_label_vec_for_gimple (labels, index_type,
> &default_case);
>
>+ bool add_bind = false;
> if (!default_case)
> {
> glabel *new_default;
>@@ -2322,14 +2344,46 @@ gimplify_switch_expr (tree *expr_p, gimp
> default_case
> = build_case_label (NULL_TREE, NULL_TREE,
> create_artificial_label (UNKNOWN_LOCATION));
>+ if (old_in_switch_expr)
>+ {
>+ SWITCH_BREAK_LABEL_P (CASE_LABEL (default_case)) = 1;
>+ add_bind = true;
>+ }
> new_default = gimple_build_label (CASE_LABEL (default_case));
> gimplify_seq_add_stmt (&switch_body_seq, new_default);
> }
>+ else if (old_in_switch_expr)
>+ {
>+ gimple *last = gimple_seq_last_stmt (switch_body_seq);
>+ if (last && gimple_code (last) == GIMPLE_LABEL)
>+ {
>+ tree label = gimple_label_label (as_a <glabel *> (last));
>+ if (SWITCH_BREAK_LABEL_P (label))
>+ add_bind = true;
>+ }
>+ }
>
> switch_stmt = gimple_build_switch (SWITCH_COND (switch_expr),
>- default_case, labels);
>- gimplify_seq_add_stmt (pre_p, switch_stmt);
>- gimplify_seq_add_seq (pre_p, switch_body_seq);
>+ default_case, labels);
>+ /* For the benefit of -Wimplicit-fallthrough, if switch_body_seq
>+ ends with a GIMPLE_LABEL holding SWITCH_BREAK_LABEL_P LABEL_DECL,
>+ wrap the GIMPLE_SWITCH up to that GIMPLE_LABEL into a GIMPLE_BIND,
>+ so that we can easily find the start and end of the switch
>+ statement. */
>+ if (add_bind)
>+ {
>+ gimple_seq bind_body = NULL;
>+ gimplify_seq_add_stmt (&bind_body, switch_stmt);
>+ gimple_seq_add_seq (&bind_body, switch_body_seq);
>+ gbind *bind = gimple_build_bind (NULL_TREE, bind_body, NULL_TREE);
>+ gimple_set_location (bind, EXPR_LOCATION (switch_expr));
>+ gimplify_seq_add_stmt (pre_p, bind);
>+ }
>+ else
>+ {
>+ gimplify_seq_add_stmt (pre_p, switch_stmt);
>+ gimplify_seq_add_seq (pre_p, switch_body_seq);
>+ }
> labels.release ();
> }
> else
>--- gcc/tree-chrec.c.jj 2017-10-11 22:37:51.000000000 +0200
>+++ gcc/tree-chrec.c 2017-11-30 20:39:01.613902149 +0100
>@@ -1161,6 +1161,7 @@ evolution_function_is_univariate_p (cons
> return false;
> break;
> }
>+ return true;
>
> default:
> return true;
>--- gcc/config/i386/i386.c.jj 2017-11-30 09:42:46.000000000 +0100
>+++ gcc/config/i386/i386.c 2017-11-30 20:40:02.484133842 +0100
>@@ -34985,6 +34985,7 @@ ix86_expand_special_args_builtin (const
> default:
> break;
> }
>+ /* FALLTHRU */
> case V64QI_FTYPE_PCCHAR_V64QI_UDI:
> case V32QI_FTYPE_PCCHAR_V32QI_USI:
> case V16QI_FTYPE_PCCHAR_V16QI_UHI:
>--- gcc/c/c-parser.c.jj 2017-11-30 12:13:49.000000000 +0100
>+++ gcc/c/c-parser.c 2017-11-30 18:35:03.735146924 +0100
>@@ -67,6 +67,7 @@ along with GCC; see the file COPYING3.
> #include "run-rtl-passes.h"
> #include "intl.h"
> #include "c-family/name-hint.h"
>+#include "tree-iterator.h"
>
> /* We need to walk over decls with incomplete struct/union/enum types
> after parsing the whole translation unit.
>@@ -5846,14 +5847,15 @@ c_parser_switch_statement (c_parser *par
>if (!open_brace_p && c_parser_peek_token (parser)->type !=
>CPP_SEMICOLON)
>warn_for_multistatement_macros (loc_after_labels, next_loc, switch_loc,
> RID_SWITCH);
>- c_finish_case (body, ce.original_type);
> if (c_break_label)
> {
> location_t here = c_parser_peek_token (parser)->location;
> tree t = build1 (LABEL_EXPR, void_type_node, c_break_label);
> SET_EXPR_LOCATION (t, here);
>- add_stmt (t);
>+ SWITCH_BREAK_LABEL_P (c_break_label) = 1;
>+ append_to_statement_list_force (t, &body);
> }
>+ c_finish_case (body, ce.original_type);
> c_break_label = save_break;
> add_stmt (c_end_compound_stmt (switch_loc, block, flag_isoc99));
> c_parser_maybe_reclassify_token (parser);
>--- gcc/cp/cp-gimplify.c.jj 2017-11-28 22:23:34.000000000 +0100
>+++ gcc/cp/cp-gimplify.c 2017-11-30 19:26:36.432776337 +0100
>@@ -330,11 +330,13 @@ genericize_switch_stmt (tree *stmt_p, in
> cp_walk_tree (&type, cp_genericize_r, data, NULL);
> *walk_subtrees = 0;
>
>+ if (TREE_USED (break_block))
>+ SWITCH_BREAK_LABEL_P (break_block) = 1;
>+ finish_bc_block (&body, bc_break, break_block);
> *stmt_p = build2_loc (stmt_locus, SWITCH_EXPR, type, cond, body);
> SWITCH_ALL_CASES_P (*stmt_p) = SWITCH_STMT_ALL_CASES_P (stmt);
> gcc_checking_assert (!SWITCH_STMT_NO_BREAK_P (stmt)
> || !TREE_USED (break_block));
>- finish_bc_block (stmt_p, bc_break, break_block);
> }
>
> /* Genericize a CONTINUE_STMT node *STMT_P. */
>--- gcc/cp/parser.c.jj 2017-11-30 09:42:44.000000000 +0100
>+++ gcc/cp/parser.c 2017-11-30 20:40:37.868687216 +0100
>@@ -29003,6 +29003,7 @@ cp_parser_objc_expression (cp_parser* pa
> default:
> break;
> }
>+ /* FALLTHRU */
> default:
> error_at (kwd->location,
> "misplaced %<@%D%> Objective-C++ construct",
>--- gcc/fortran/match.c.jj 2017-10-28 09:00:47.000000000 +0200
>+++ gcc/fortran/match.c 2017-11-30 20:41:45.464834013 +0100
>@@ -1240,6 +1240,7 @@ loop:
> default:
> gfc_internal_error ("gfc_match(): Bad match code %c", c);
> }
>+ /* FALLTHRU */
>
> default:
>
>--- gcc/testsuite/c-c++-common/Wimplicit-fallthrough-7.c.jj 2017-04-28
>22:17:03.000000000 +0200
>+++ gcc/testsuite/c-c++-common/Wimplicit-fallthrough-7.c 2017-11-30
>19:14:47.535557117 +0100
>@@ -51,9 +51,9 @@ f (int i)
> {
> case 1:
> {
>- switch (i + 2)
>+ switch (i + 2) /* { dg-warning "statement may fall through" } */
> case 4:
>- bar (1); /* { dg-warning "statement may fall through" } */
>+ bar (1);
> case 5:
> bar (5);
> return;
>--- gcc/testsuite/c-c++-common/Wimplicit-fallthrough-36.c.jj 2017-11-30
>19:11:32.029979082 +0100
>+++ gcc/testsuite/c-c++-common/Wimplicit-fallthrough-36.c 2017-11-30
>19:11:07.000000000 +0100
>@@ -0,0 +1,72 @@
>+/* PR c/79153 */
>+/* { dg-do compile } */
>+/* { dg-options "-Wimplicit-fallthrough" } */
>+
>+int
>+test (int v1, int v2)
>+{
>+ switch (v1)
>+ {
>+ case 3:
>+ switch (v2) /* { dg-warning "this statement may fall through" }
>*/
>+ {
>+ case 1:
>+ return 28;
>+ case 2:
>+ return 38;
>+ case 3:
>+ return 88;
>+ default:
>+ break;
>+ }
>+ case 4: /* { dg-message "here" } */
>+ return 168;
>+ case 5:
>+ switch (v2) /* { dg-warning "this statement may fall through" }
>*/
>+ {
>+ case 4:
>+ break;
>+ case 5:
>+ return 38;
>+ case 6:
>+ return 88;
>+ }
>+ case 6: /* { dg-message "here" } */
>+ return 169;
>+ case 7:
>+ switch (v2) /* { dg-warning "this statement may fall through" }
>*/
>+ {
>+ case 7:
>+ return 38;
>+ case 8:
>+ return 88;
>+ }
>+ case 8: /* { dg-message "here" } */
>+ return 170;
>+ case 9:
>+ switch (v2) /* { dg-bogus "this statement may fall through" } */
>+ {
>+ case 9:
>+ return 38;
>+ case 10:
>+ return 88;
>+ default:
>+ return 89;
>+ }
>+ case 10:
>+ return 171;
>+ case 11:
>+ switch (v2) /* { dg-bogus "this statement may fall through" } */
>+ {
>+ case -__INT_MAX__ - 1 ... 31:
>+ return 38;
>+ case 32:
>+ return 88;
>+ case 33 ... __INT_MAX__:
>+ return 89;
>+ }
>+ case 12:
>+ return 172;
>+ }
>+ return -1;
>+}
>
> Jakub
