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C++ PATCH for c++/86184, rejects-valid with ?: and omitted operand
- From: Marek Polacek <polacek at redhat dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>, Jason Merrill <jason at redhat dot com>
- Date: Thu, 21 Jun 2018 14:22:31 -0400
- Subject: C++ PATCH for c++/86184, rejects-valid with ?: and omitted operand
The following testcase is rejected because, for this line:
bool b = X() ?: false;
arg2 is missing and arg1 is a TARGET_EXPR. A TARGET_EXPR is a class
prvalue so we wrap it in a SAVE_EXPR. Later when building 'this' we
call build_this (SAVE_EXPR <TARGET_EXPR <...>>) which triggers lvalue_error:
5856 cp_lvalue_kind kind = lvalue_kind (arg);
5857 if (kind == clk_none)
5858 {
5859 if (complain & tf_error)
5860 lvalue_error (input_location, lv_addressof);
because all SAVE_EXPRs are non-lvalue.
Since
a) cp_build_addr_expr_1 can process xvalues and class prvalues,
b) TARGET_EXPRs are only evaluated once (gimplify_target_expr),
I thought we could do the following. The testcase ensures that
with the omitted operand we only construct X once.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2018-06-21 Marek Polacek <polacek@redhat.com>
PR c++/86184
* call.c (build_conditional_expr_1): Don't wrap TARGET_EXPRs
in a SAVE_EXPR.
* g++.dg/ext/cond3.C: New test.
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -4806,6 +4806,10 @@ build_conditional_expr_1 (location_t loc, tree arg1, tree arg2, tree arg3,
/* Make sure that lvalues remain lvalues. See g++.oliva/ext1.C. */
if (lvalue_p (arg1))
arg2 = arg1 = cp_stabilize_reference (arg1);
+ else if (TREE_CODE (arg1) == TARGET_EXPR)
+ /* TARGET_EXPRs are only expanded once, don't wrap it in a SAVE_EXPR,
+ rendering it clk_none of clk_class. */
+ arg2 = arg1;
else
arg2 = arg1 = cp_save_expr (arg1);
}
--- gcc/testsuite/g++.dg/ext/cond3.C
+++ gcc/testsuite/g++.dg/ext/cond3.C
@@ -0,0 +1,20 @@
+// PR c++/86184
+// { dg-do run }
+// { dg-options "" }
+
+int j;
+struct X {
+ X() { j++; }
+ operator bool() { return true; }
+};
+
+/* Only create X once. */
+bool b = X() ?: false;
+bool b2 = X() ? X() : false;
+
+int
+main ()
+{
+ if (j != 3)
+ __builtin_abort ();
+}