On Fri, Apr 22, 2016 at 09:43:31AM -0400, Jason Merrill wrote:
> On 04/22/2016 07:50 AM, Marek Polacek wrote:
> >This PR shows that we generate wrong code with the x ?: y extension in case
> >the
> >first operand contains either predecrement or preincrement. The problem is
> >that we don't emit SAVE_EXPR, thus the operand is evaluated twice, which it
> >should not be.
> >
> >While ++i or --i can be lvalues in C++, i++ or i-- can not. The code in
> >build_conditional_expr_1 has:
> > 4635 /* Make sure that lvalues remain lvalues. See
> > g++.oliva/ext1.C. */
> > 4636 if (real_lvalue_p (arg1))
> > 4637 arg2 = arg1 = stabilize_reference (arg1);
> > 4638 else
> > 4639 arg2 = arg1 = save_expr (arg1);
> >so for ++i/--i we call stabilize_reference, but that doesn't know anything
> >about PREINCREMENT_EXPR or PREDECREMENT_EXPR and just returns the same
> >expression, so SAVE_EXPR isn't created.
> >
> >I think one fix would be to teach stabilize_reference what to do with those,
> >similarly to how we handle COMPOUND_EXPR there.
>
> Your change will turn the expression into an rvalue, so that isn't enough.
Oops.
> We need to turn the expression into some sort of _REF before passing it to
> stabilize_reference, perhaps by factoring out the cast-to-reference code
> from force_paren_expr. This should probably be part of a
> cp_stabilize_reference function that replaces all uses of
> stabilize_reference in the front end.
Thanks, this magic seems to work. So something like the following? I didn't
put the cast-to-reference code into its separate function because it didn't
seem convenient, but I can work on that, too, if you prefer.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2016-04-22 Marek Polacek <pola...@redhat.com>
PR c++/70744
* call.c (build_conditional_expr_1): Call cp_stabilize_reference
instead of stabilize_reference.
(build_over_call): Likewise.
* cp-tree.h (cp_stabilize_reference): Declare.
* tree.c (cp_stabilize_reference): New function.
* typeck.c (cp_build_unary_op): Call cp_stabilize_reference instead of
stabilize_reference.
(unary_complex_lvalue): Likewise.
(cp_build_modify_expr): Likewise.
* g++.dg/ext/cond2.C: New test.
diff --git gcc/cp/call.c gcc/cp/call.c
index 11f2d42..476e806 100644
--- gcc/cp/call.c
+++ gcc/cp/call.c
@@ -4634,7 +4634,7 @@ 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 (real_lvalue_p (arg1))
- arg2 = arg1 = stabilize_reference (arg1);
+ arg2 = arg1 = cp_stabilize_reference (arg1);
else
arg2 = arg1 = save_expr (arg1);
}
@@ -7644,8 +7644,9 @@ build_over_call (struct z_candidate *cand, int flags,
tsubst_flags_t complain)
|| (TREE_CODE (arg) == TARGET_EXPR
&& !unsafe_copy_elision_p (fa, arg)))
{
- tree to = stabilize_reference (cp_build_indirect_ref (fa, RO_NULL,
- complain));
+ tree to = cp_stabilize_reference (cp_build_indirect_ref (fa,
+ RO_NULL,
+ complain));
val = build2 (INIT_EXPR, DECL_CONTEXT (fn), to, arg);
return val;
@@ -7655,7 +7656,7 @@ build_over_call (struct z_candidate *cand, int flags,
tsubst_flags_t complain)
&& trivial_fn_p (fn)
&& !DECL_DELETED_FN (fn))
{
- tree to = stabilize_reference
+ tree to = cp_stabilize_reference
(cp_build_indirect_ref (argarray[0], RO_NULL, complain));
tree type = TREE_TYPE (to);
tree as_base = CLASSTYPE_AS_BASE (type);
diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
index ec92718..0e46ae1 100644
--- gcc/cp/cp-tree.h
+++ gcc/cp/cp-tree.h
@@ -6494,6 +6494,7 @@ extern cp_lvalue_kind real_lvalue_p
(const_tree);
extern cp_lvalue_kind lvalue_kind (const_tree);
extern bool lvalue_or_rvalue_with_address_p (const_tree);
extern bool xvalue_p (const_tree);
+extern tree cp_stabilize_reference (tree);
extern bool builtin_valid_in_constant_expr_p (const_tree);
extern tree build_min (enum tree_code, tree, ...);
extern tree build_min_nt_loc (location_t, enum tree_code,
diff --git gcc/cp/tree.c gcc/cp/tree.c
index 112c8c7..44e3893 100644
--- gcc/cp/tree.c
+++ gcc/cp/tree.c
@@ -296,6 +296,31 @@ xvalue_p (const_tree ref)
return (lvalue_kind (ref) == clk_rvalueref);
}
+/* C++-specific version of stabilize_reference. For preincrement and
+ predecrement expressions we need to turn the expression into some
+ sort of _REF before passing it to stabilize_reference. */
+
+tree
+cp_stabilize_reference (tree ref)
+{
+ if (TREE_CODE (ref) == PREINCREMENT_EXPR
+ || TREE_CODE (ref) == PREDECREMENT_EXPR)
+ {
+ cp_lvalue_kind kind = lvalue_kind (ref);
+ if ((kind & ~clk_class) != clk_none)
+ {
+ tree type = unlowered_expr_type (ref);
+ bool rval = !!(kind & clk_rvalueref);
+ type = cp_build_reference_type (type, rval);
+ /* This inhibits warnings in, eg, cxx_mark_addressable
+ (c++/60955). */
+ warning_sentinel s (extra_warnings);
+ ref = build_static_cast (type, ref, tf_error);
+ }
+ }
+ return stabilize_reference (ref);
+}
+
/* Test whether DECL is a builtin that may appear in a
constant-expression. */
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index cef5604..7e12009 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -5912,7 +5912,7 @@ cp_build_unary_op (enum tree_code code, tree xarg, int
noconvert,
{
tree real, imag;
- arg = stabilize_reference (arg);
+ arg = cp_stabilize_reference (arg);
real = cp_build_unary_op (REALPART_EXPR, arg, 1, complain);
imag = cp_build_unary_op (IMAGPART_EXPR, arg, 1, complain);
real = cp_build_unary_op (code, real, 1, complain);
@@ -6112,7 +6112,7 @@ unary_complex_lvalue (enum tree_code code, tree arg)
tree lvalue = TREE_OPERAND (arg, 0);
if (TREE_SIDE_EFFECTS (lvalue))
{
- lvalue = stabilize_reference (lvalue);
+ lvalue = cp_stabilize_reference (lvalue);
arg = build2 (TREE_CODE (arg), TREE_TYPE (arg),
lvalue, TREE_OPERAND (arg, 1));
}
@@ -7496,7 +7496,7 @@ cp_build_modify_expr (tree lhs, enum tree_code
modifycode, tree rhs,
case PREINCREMENT_EXPR:
if (TREE_SIDE_EFFECTS (TREE_OPERAND (lhs, 0)))
lhs = build2 (TREE_CODE (lhs), TREE_TYPE (lhs),
- stabilize_reference (TREE_OPERAND (lhs, 0)),
+ cp_stabilize_reference (TREE_OPERAND (lhs, 0)),
TREE_OPERAND (lhs, 1));
newrhs = cp_build_modify_expr (TREE_OPERAND (lhs, 0),
modifycode, rhs, complain);
@@ -7516,7 +7516,7 @@ cp_build_modify_expr (tree lhs, enum tree_code
modifycode, tree rhs,
case MODIFY_EXPR:
if (TREE_SIDE_EFFECTS (TREE_OPERAND (lhs, 0)))
lhs = build2 (TREE_CODE (lhs), TREE_TYPE (lhs),
- stabilize_reference (TREE_OPERAND (lhs, 0)),
+ cp_stabilize_reference (TREE_OPERAND (lhs, 0)),
TREE_OPERAND (lhs, 1));
newrhs = cp_build_modify_expr (TREE_OPERAND (lhs, 0), modifycode, rhs,
complain);
@@ -7665,7 +7665,7 @@ cp_build_modify_expr (tree lhs, enum tree_code
modifycode, tree rhs,
not intervene between the lvalue-to-rvalue conversion and the
side effect associated with any single compound assignment
operator. -- end note ] */
- lhs = stabilize_reference (lhs);
+ lhs = cp_stabilize_reference (lhs);
rhs = rvalue (rhs);
rhs = stabilize_expr (rhs, &init);
newrhs = cp_build_binary_op (input_location,
diff --git gcc/testsuite/g++.dg/ext/cond2.C gcc/testsuite/g++.dg/ext/cond2.C
index e69de29..d9f1d59 100644
--- gcc/testsuite/g++.dg/ext/cond2.C
+++ gcc/testsuite/g++.dg/ext/cond2.C
@@ -0,0 +1,28 @@
+// PR c++/70744
+// { dg-do run }
+// { dg-options "" }
+
+static void
+fn1 (void)
+{
+ int x = 2;
+ ++x ? : 42;
+ if (x != 3)
+ __builtin_abort ();
+ --x ? : 42;
+ if (x != 2)
+ __builtin_abort ();
+ x++ ? : 42;
+ if (x != 3)
+ __builtin_abort ();
+ x-- ? : 42;
+ if (x != 2)
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+ fn1 ();
+ return 0;
+}
Marek
