@@ -2250,9 +2250,9 @@ last_stmt_in_scope (gimple *stmt)
}
}
-/* Collect interesting labels in LABELS and return the statement preceding
- another case label, or a user-defined label. Store a location useful
- to give warnings at *PREVLOC (usually the location of the returned
+/* Collect labels that may fall through into LABELS and return the statement
+ preceding another case label, or a user-defined label. Store a location
+ useful to give warnings at *PREVLOC (usually the location of the returned
statement or of its surrounding scope). */
static gimple *
@@ -2331,8 +2331,12 @@ collect_fallthrough_labels (gimple_stmt_iterator *gsi_p,
if (gsi_end_p (*gsi_p))
break;
- struct label_entry l = { false_lab, if_loc };
- labels->safe_push (l);
+ /* A dead label can't fall through. */
+ if (!UNUSED_LABEL_P (false_lab))
+ {
+ struct label_entry l = { false_lab, if_loc };
+ labels->safe_push (l);
+ }
/* Go to the last statement of the then branch. */
gsi_prev (gsi_p);
@@ -2359,6 +2363,17 @@ collect_fallthrough_labels (gimple_stmt_iterator *gsi_p,
labels->safe_push (l);
}
}
+ /* This case is about
+ if (1 != 0) goto <D.2022>; else goto <D.2023>;
+ <D.2022>:
+ n = n + 1; // #1
+ <D.2023>: // #2
+ <D.1988>: // #3
+ where #2 is UNUSED_LABEL_P and we want to warn about #1 falling
+ through to #3. So set PREV to #1. */
+ else if (UNUSED_LABEL_P (false_lab))
+ prev = gsi_stmt (*gsi_p);
+
/* And move back. */
gsi_next (gsi_p);
}
@@ -4461,9 +4476,19 @@ gimplify_cond_expr (tree *expr_p, gimple_seq *pre_p, fallback_t fallback)
if (TREE_OPERAND (expr, 1) == NULL_TREE
&& !have_else_clause_p
&& TREE_OPERAND (expr, 2) != NULL_TREE)
- label_cont = label_true;
+ {
+ /* For if (0) {} else { code; } tell -Wimplicit-fallthrough
+ handling that label_cont == label_true can be only reached
+ through fallthrough from { code; }. */
+ if (integer_zerop (COND_EXPR_COND (expr)))
+ UNUSED_LABEL_P (label_true) = 1;
+ label_cont = label_true;
+ }
else
{
+ bool then_side_effects
+ = (TREE_OPERAND (expr, 1)
+ && TREE_SIDE_EFFECTS (TREE_OPERAND (expr, 1)));
gimplify_seq_add_stmt (&seq, gimple_build_label (label_true));
have_then_clause_p = gimplify_stmt (&TREE_OPERAND (expr, 1), &seq);
/* For if (...) { code; } else {} or
@@ -4477,6 +4502,16 @@ gimplify_cond_expr (tree *expr_p, gimple_seq *pre_p, fallback_t fallback)
gimple *g;
label_cont = create_artificial_label (UNKNOWN_LOCATION);
+ /* For if (0) { non-side-effect-code } else { code }
+ tell -Wimplicit-fallthrough handling that label_cont can
+ be only reached through fallthrough from { code }. */
+ if (integer_zerop (COND_EXPR_COND (expr)))
+ {
+ UNUSED_LABEL_P (label_true) = 1;
+ if (!then_side_effects)
+ UNUSED_LABEL_P (label_cont) = 1;
+ }
+
g = gimple_build_goto (label_cont);
/* GIMPLE_COND's are very low level; they have embedded
@@ -4493,6 +4528,13 @@ gimplify_cond_expr (tree *expr_p, gimple_seq *pre_p, fallback_t fallback)
}
if (!have_else_clause_p)
{
+ /* For if (1) { code } or if (1) { code } else { non-side-effect-code }
+ tell -Wimplicit-fallthrough handling that label_false can be only
+ reached through fallthrough from { code }. */
+ if (integer_nonzerop (COND_EXPR_COND (expr))
+ && (TREE_OPERAND (expr, 2) == NULL_TREE
+ || !TREE_SIDE_EFFECTS (TREE_OPERAND (expr, 2))))
+ UNUSED_LABEL_P (label_false) = 1;
gimplify_seq_add_stmt (&seq, gimple_build_label (label_false));
have_else_clause_p = gimplify_stmt (&TREE_OPERAND (expr, 2), &seq);
}
new file mode 100644
@@ -0,0 +1,140 @@
+/* PR middle-end/103597 */
+/* { dg-do compile } */
+/* { dg-options "-Wimplicit-fallthrough" } */
+
+#define E(c, e) if (c) e
+
+int
+fn0 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ E (1, return 0);
+ case 1:
+ return -1;
+ }
+ return 0;
+}
+
+int
+fn1 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ E (1, goto out);
+ case 1:
+ return -1;
+ }
+out:
+ return 0;
+}
+
+int
+fn2 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ if (1) /* { dg-warning "statement may fall through" "" { target c++ } } */
+ n++; /* { dg-warning "statement may fall through" "" { target c } } */
+ case 1: /* { dg-message "here" } */
+ return -1;
+ }
+ return 0;
+}
+
+int
+fn3 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ if (0) /* { dg-warning "statement may fall through" } */
+ return 0;
+ case 1: /* { dg-message "here" } */
+ return -1;
+ }
+ return 0;
+}
+
+int
+fn4 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ E (0, n++);
+ --n; /* { dg-warning "statement may fall through" } */
+ case 1: /* { dg-message "here" } */
+ return -1;
+ }
+ return 0;
+}
+
+int
+fn5 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ if (1)
+ return 0;
+ else
+ return -1;
+ case 1:
+ return -1;
+ }
+ return 0;
+}
+
+int
+fn6 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ if (1)
+ return 0;
+ else
+ {
+meow:
+ n--; /* { dg-warning "statement may fall through" } */
+ }
+ case 1: /* { dg-message "here" } */
+ return -1;
+ case 2:
+ goto meow;
+ }
+ return 0;
+}
+
+int
+fn7 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ if (1)
+ return 0;
+woof:
+ case 1:
+ return -1;
+ }
+ return 0;
+}
+
+int
+fn8 (int n)
+{
+ switch (n)
+ {
+ case 0:
+ if (1) n++; /* { dg-warning "statement may fall through" } */
+woof: /* { dg-message "here" } */
+ case 1:
+ return -1;
+ }
+ return 0;
+}
@@ -787,6 +787,12 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
#define SWITCH_BREAK_LABEL_P(NODE) \
(LABEL_DECL_CHECK (NODE)->base.protected_flag)
+/* Set on label that is known not to be jumped to, it can be only
+ reached by falling through from previous statements.
+ This is used to implement -Wimplicit-fallthrough. */
+#define UNUSED_LABEL_P(NODE) \
+ (LABEL_DECL_CHECK (NODE)->base.default_def_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.
This patch fixes a wrong -Wimplicit-fallthrough warning for case 0: if (1) // wrong may fallthrough return 0; case 1: which in .gimple looks like <D.1981>: // case 0 if (1 != 0) goto <D.1985>; else goto <D.1986>; <D.1985>: D.1987 = 0; // predicted unlikely by early return (on trees) predictor. return D.1987; <D.1986>: // dead <D.1982>: // case 1 and the warning thinks that <D.1986>: falls through to <D.1982>:. It does not know that <D.1986> is effectively a dead label, only reachable through fallthrough from previous instructions, never jumped to. To that effect, Jakub introduced UNUSED_LABEL_P, which is set on such dead labels. collect_fallthrough_labels has code to deal with cases like case 2: if (e != 10) i++; // this may fallthru, warn else return 44; case 3: which collects labels that may fall through. Here it sees the "goto <D.1990>;" at the end of the then branch and so when the warning reaches ... <D.1990>: // from if-then <D.1984>: // case 3 it knows it should warn about the possible fallthrough. But an UNUSED_LABEL_P is not a label that can fallthrough like that, so it should ignore those. However, we still want to warn about this: case 0: if (1) n++; // falls through case 1: so collect_fallthrough_labels needs to return the "n = n + 1;" statement, rather than the dead label. Co-authored-by: Jakub Jelinek <jakub@redhat.com> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? PR middle-end/103597 gcc/ChangeLog: * gimplify.cc (collect_fallthrough_labels): Don't push UNUSED_LABEL_Ps into labels. Maybe set prev to the statement preceding UNUSED_LABEL_P. (gimplify_cond_expr): Set UNUSED_LABEL_P. * tree.h (UNUSED_LABEL_P): New. gcc/testsuite/ChangeLog: * c-c++-common/Wimplicit-fallthrough-39.c: New test. --- gcc/gimplify.cc | 54 ++++++- .../c-c++-common/Wimplicit-fallthrough-39.c | 140 ++++++++++++++++++ gcc/tree.h | 6 + 3 files changed, 194 insertions(+), 6 deletions(-) create mode 100644 gcc/testsuite/c-c++-common/Wimplicit-fallthrough-39.c base-commit: 1dca4ca1bf2f1b05537a1052e373d8b0ff11e53c