On 9/18/23 12:12, Patrick Palka wrote:
Jason pointed out that even implicit loads of volatile references need
to undergo lvalue-to-rvalue conversion, but we currently emit a warning
in this case and discard the load. This patch changes this behavior so
that we don't issue a warning, and preserve the load.
gcc/cp/ChangeLog:
* cvt.cc (convert_to_void) <case INDIRECT_REF>: Remove warning
for an implicit load of a volatile reference. Simplify as if
is_reference is false. Check REFERENCE_REF_P in the test
guarding the -Wunused-value diagnostic.
gcc/testsuite/ChangeLog:
* g++.dg/expr/discarded1a.C: No longer expect warning for
implicit load of a volatile reference.
* g++.old-deja/g++.bugs/900428_01.C: Likewise.
* g++.dg/expr/volatile2.C: New test.
---
gcc/cp/cvt.cc | 56 ++-----------------
gcc/testsuite/g++.dg/expr/discarded1a.C | 1 -
gcc/testsuite/g++.dg/expr/volatile2.C | 12 ++++
.../g++.old-deja/g++.bugs/900428_01.C | 26 ++++-----
4 files changed, 30 insertions(+), 65 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/expr/volatile2.C
diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index 4424670356c..1cb6c1222c2 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -1251,12 +1251,9 @@ convert_to_void (tree expr, impl_conv_void implicit,
tsubst_flags_t complain)
{
tree type = TREE_TYPE (expr);
int is_volatile = TYPE_VOLATILE (type);
- if (is_volatile)
- complete_type (type);
- int is_complete = COMPLETE_TYPE_P (type);
/* Can't load the value if we don't know the type. */
- if (is_volatile && !is_complete)
+ if (is_volatile && !COMPLETE_TYPE_P (complete_type (type)))
{
if (complain & tf_warning)
switch (implicit)
@@ -1298,50 +1295,7 @@ convert_to_void (tree expr, impl_conv_void implicit,
tsubst_flags_t complain)
gcc_unreachable ();
}
}
- /* Don't load the value if this is an implicit dereference, or if
- the type needs to be handled by ctors/dtors. */
- else if (is_volatile && is_reference)
- {
- if (complain & tf_warning)
- switch (implicit)
- {
- case ICV_CAST:
- warning_at (loc, 0, "conversion to void will not access "
- "object of type %qT", type);
- break;
- case ICV_SECOND_OF_COND:
- warning_at (loc, 0, "implicit dereference will not access "
- "object of type %qT in second operand of "
- "conditional expression", type);
- break;
- case ICV_THIRD_OF_COND:
- warning_at (loc, 0, "implicit dereference will not access "
- "object of type %qT in third operand of "
- "conditional expression", type);
- break;
- case ICV_RIGHT_OF_COMMA:
- warning_at (loc, 0, "implicit dereference will not access "
- "object of type %qT in right operand of "
- "comma operator", type);
- break;
- case ICV_LEFT_OF_COMMA:
- warning_at (loc, 0, "implicit dereference will not access "
- "object of type %qT in left operand of comma "
- "operator", type);
- break;
- case ICV_STATEMENT:
- warning_at (loc, 0, "implicit dereference will not access "
- "object of type %qT in statement", type);
- break;
- case ICV_THIRD_IN_FOR:
- warning_at (loc, 0, "implicit dereference will not access "
- "object of type %qT in for increment
expression",
- type);
- break;
- default:
- gcc_unreachable ();
- }
- }
+ /* Don't load the value if the type needs to be handled by cdtors. */
else if (is_volatile && TREE_ADDRESSABLE (type))
{
if (complain & tf_warning)
@@ -1386,7 +1340,7 @@ convert_to_void (tree expr, impl_conv_void implicit,
tsubst_flags_t complain)
gcc_unreachable ();
}
}
- if (is_reference || !is_volatile || !is_complete || TREE_ADDRESSABLE
(type))
+ if (!is_volatile || !COMPLETE_TYPE_P (type))
{
/* Emit a warning (if enabled) when the "effect-less" INDIRECT_REF
operation is stripped off. Note that we don't warn about
@@ -1397,8 +1351,8 @@ convert_to_void (tree expr, impl_conv_void implicit,
tsubst_flags_t complain)
if (warn_unused_value
&& implicit != ICV_CAST
&& (complain & tf_warning)
- && !warning_suppressed_p (expr, OPT_Wunused_value)
- && !is_reference)
+ && !warning_suppressed_p (expr, OPT_Wunused_value)
+ && !REFERENCE_REF_P (expr))
warning_at (loc, OPT_Wunused_value, "value computed is not
used");
expr = TREE_OPERAND (expr, 0);
if (TREE_CODE (expr) == CALL_EXPR
diff --git a/gcc/testsuite/g++.dg/expr/discarded1a.C
b/gcc/testsuite/g++.dg/expr/discarded1a.C
index 1c4dff4553e..4754f32f716 100644
--- a/gcc/testsuite/g++.dg/expr/discarded1a.C
+++ b/gcc/testsuite/g++.dg/expr/discarded1a.C
@@ -12,6 +12,5 @@ extern volatile Holder<Incomplete, 2>* c;
int main() {
a; // { dg-message "required from here" }
b; // { dg-message "required from here" }
- // { dg-warning "implicit dereference will not access object" "" { target
*-*-* } .-1 }
*c; // { dg-message "required from here" }
}
diff --git a/gcc/testsuite/g++.dg/expr/volatile2.C
b/gcc/testsuite/g++.dg/expr/volatile2.C
new file mode 100644
index 00000000000..62e609aee2f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/expr/volatile2.C
@@ -0,0 +1,12 @@
+// Verify we preserve implicit loads of volatile references in a
+// discarded-value expression.
+// { dg-additional-options "-O -fdump-tree-original -fdump-tree-optimized" }
+// { dg-final { scan-tree-dump {\*a} "original" } }
+// { dg-final { scan-tree-dump {\*a} "optimized" } }
+
+struct A { int m; };
+extern volatile A& a;
+
+int main() {
+ a;
+}
diff --git a/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C
b/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C
index a806ef0706e..2b82c64ff73 100644
--- a/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C
+++ b/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C
@@ -46,16 +46,16 @@ void int_test (int i, int *p, volatile int *vp, int &r,
volatile int &vr)
(void)(i ? r : j); // ok, no warning
(void)((void)1, r); // ok, no warning
- vr; // { dg-warning "" } reference not accessed
- (void)vr; // { dg-warning "" } reference not accessed
- (void)(i ? vj : vr); // { dg-warning "" } reference not accessed
- (void)(i ? vr : vj); // { dg-warning "" } reference not accessed
- (void)((void)1, vr); // { dg-warning "" } reference not accessed
+ vr; // ok, no warning
+ (void)vr; // ok, no warning
+ (void)(i ? vj : vr); // ok, no warning
+ (void)(i ? vr : vj); // ok, no warning
+ (void)((void)1, vr); // ok, no warning
*ip_fn (); // ok, no warning
*vip_fn (); // ok, no warning
ir_fn (); // ok, no warning
- vir_fn (); // { dg-warning "" } reference not accessed
+ vir_fn (); // ok, no warning
This should still warn (and not load), a function call is not one of the
forms in https://eel.is/c++draft/expr#context-2. We still need the
warnings you're removing for expression forms that aren't on that list.
}
struct S;
@@ -128,16 +128,16 @@ void complete_test (int i, T *p, volatile T *vp, T &r,
volatile T &vr)
(void)(i ? r : j); // ok, no warning
(void)((void)1, r); // ok, no warning
- vr; // { dg-warning "" } reference not accessed
- (void)vr; // { dg-warning "" } reference not accessed
- (void)(i ? vj : vr); // { dg-warning "" } reference not accessed
- (void)(i ? vr : vj); // { dg-warning "" } reference not accessed
- (void)((void)1, vr); // { dg-warning "" } reference not accessed
+ vr; // ok, no warning
+ (void)vr; // ok, no warning
+ (void)(i ? vj : vr); // ok, no warning
+ (void)(i ? vr : vj); // ok, no warning
+ (void)((void)1, vr); // ok, no warning
*tp_fn (); // ok, no warning
*vtp_fn (); // ok, no warning
tr_fn (); // ok, no warning
- vtr_fn (); // ok, no warning{ dg-warning "" } reference
not accessed
+ vtr_fn (); // ok, no warning
Likewise.
}
void extern_test ()
@@ -160,5 +160,5 @@ void extern_test ()
esr; // ok, no warning
vesr; // { dg-warning "" } incomplete not
accessed
etr; // ok, no warning
- vetr; // { dg-warning "" } reference not
accessed
+ vetr; // ok, no warning
}
