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[PATCH] to gimplify_cond_expr for PR c++/86485 - -Wmaybe-unused with empty class ?:
- From: Jason Merrill <jason at redhat dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Tue, 5 Mar 2019 17:20:24 -0500
- Subject: [PATCH] to gimplify_cond_expr for PR c++/86485 - -Wmaybe-unused with empty class ?:
Well, this sent me down rather a rabbit hole of empty class handling.
The main problem in this testcase is that the front end expects an rvalue
COND_EXPR to initialize a single temporary from one of the arms. But
because gimplify_cond_expr used MODIFY_EXPR, instead the arms would each
create their own temporary and then copy that into the common temporary.
So, let's use INIT_EXPR instead. Other issues I came across will wait for
stage 1.
Tested x86_64-pc-linux-gnu, applying to trunk.
* gimplify.c (gimplify_cond_expr): Use INIT_EXPR.
---
gcc/gimplify.c | 4 ++--
gcc/testsuite/g++.dg/init/empty2.C | 12 ++++++++++++
gcc/ChangeLog | 5 +++++
3 files changed, 19 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/init/empty2.C
diff --git a/gcc/gimplify.c b/gcc/gimplify.c
index 983635ba21f..fa85b1c86de 100644
--- a/gcc/gimplify.c
+++ b/gcc/gimplify.c
@@ -4024,11 +4024,11 @@ gimplify_cond_expr (tree *expr_p, gimple_seq *pre_p, fallback_t fallback)
/* Build the new then clause, `tmp = then_;'. But don't build the
assignment if the value is void; in C++ it can be if it's a throw. */
if (!VOID_TYPE_P (TREE_TYPE (then_)))
- TREE_OPERAND (expr, 1) = build2 (MODIFY_EXPR, type, tmp, then_);
+ TREE_OPERAND (expr, 1) = build2 (INIT_EXPR, type, tmp, then_);
/* Similarly, build the new else clause, `tmp = else_;'. */
if (!VOID_TYPE_P (TREE_TYPE (else_)))
- TREE_OPERAND (expr, 2) = build2 (MODIFY_EXPR, type, tmp, else_);
+ TREE_OPERAND (expr, 2) = build2 (INIT_EXPR, type, tmp, else_);
TREE_TYPE (expr) = void_type_node;
recalculate_side_effects (expr);
diff --git a/gcc/testsuite/g++.dg/init/empty2.C b/gcc/testsuite/g++.dg/init/empty2.C
new file mode 100644
index 00000000000..f0d8e3fec01
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/empty2.C
@@ -0,0 +1,12 @@
+// PR c++/86485
+// { dg-additional-options -Wmaybe-uninitialized }
+
+struct E {};
+struct S { S () {} E e; };
+void foo (S);
+
+void
+bar (bool b)
+{
+ foo (b ? S () : S ());
+}
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 405bc38fb75..df50f599d1a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2019-03-02 Jason Merrill <jason@redhat.com>
+
+ PR c++/86485 - -Wmaybe-unused with empty class ?:
+ * gimplify.c (gimplify_cond_expr): Use INIT_EXPR.
+
2019-03-05 Jakub Jelinek <jakub@redhat.com>
PR target/89587
base-commit: cd5a9ed1f359703439b230d251e0a2bbfd49d100
--
2.20.1