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[PATCH] c++: Fix spurious fallthrough warning on break
- From: Siddhesh Poyarekar <siddhesh at sourceware dot org>
- To: gcc-patches at gcc dot gnu dot org
- Date: Mon, 19 Feb 2018 21:59:00 +0530
- Subject: [PATCH] c++: Fix spurious fallthrough warning on break
- Authentication-results: sourceware.org; auth=none
The C++ frontend generates a break that results in the fallthrough
warning misfiring in nested switch blocks where cases in the inner
switch block return, rendering the break pointless. The fallthrough
detection in finish_break_stmt does not work either because the
condition is encoded as an IF_STMT and not a COND_EXPR.
Fix this by adding a condition for IF_STMT in the
langhooks.block_may_fallthru for C++. Fix tested on x86_64. Full
testsuite run is in progress.
Siddhesh
gcc/cp
* cp-objcp-common.c (cxx_block_may_fallthru): Add case for
IF_STMT.
gcc/testsuite
* g++.dg/nested-switch.C: New test case.
---
gcc/cp/cp-objcp-common.c | 5 +++++
gcc/testsuite/g++.dg/nested-switch.C | 30 ++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/nested-switch.C
diff --git a/gcc/cp/cp-objcp-common.c b/gcc/cp/cp-objcp-common.c
index a45dda4d012..5289a89e486 100644
--- a/gcc/cp/cp-objcp-common.c
+++ b/gcc/cp/cp-objcp-common.c
@@ -349,6 +349,11 @@ cxx_block_may_fallthru (const_tree stmt)
case THROW_EXPR:
return false;
+ case IF_STMT:
+ if (block_may_fallthru (THEN_CLAUSE (stmt)))
+ return true;
+ return block_may_fallthru (ELSE_CLAUSE (stmt));
+
case SWITCH_STMT:
return (!SWITCH_STMT_ALL_CASES_P (stmt)
|| !SWITCH_STMT_NO_BREAK_P (stmt)
diff --git a/gcc/testsuite/g++.dg/nested-switch.C b/gcc/testsuite/g++.dg/nested-switch.C
new file mode 100644
index 00000000000..46412dd293f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/nested-switch.C
@@ -0,0 +1,30 @@
+// Verify that there are no spurious warnings in nested switch statements due
+// to the unnecessary break in the inner switch block.
+// { dg-do compile }
+// { dg-options "-Werror=implicit-fallthrough" } */
+
+int
+foo (int c1, int c2, int c3)
+{
+ switch (c2)
+ {
+ case 0:
+ switch (c3) {
+ case 0:
+ if (c1)
+ return 1;
+ else
+ return 2;
+ break;
+
+ default:
+ return 3;
+ }
+
+ case 1:
+ return 4;
+ default:
+ return 5;
+ break;
+ }
+}
--
2.14.3