Hi,
This patch fixes an issue in the C frontend wherein the result of a
cast-expression sometimes retains the type qualifiers of the operand
type. It is incorrect for a cast-expression to have a qualified type
because cast-expressions are rvalues.
This incorrect semantics can be seen through use of the typeof()
operator:
const int x;
typeof ((int) x) y = 0; /* y erroneously has the type const int */
y = 1; /* error */
const int x;
typeof ((const int) x) y = 0; /* y erroneously has the type const int */
y = 1; /* error */
I think that in either of these two cases, y should have type int.
Instead it currently has type const int because x's type qualifiers are
retained "through" the cast-expression.
Note that the current behavior is not only wrong, but inconsistently
wrong: if one replaces "(int)" with "(long)" and "(const int)" with
"(const long)" in the above examples then neither of them emit an error:
const int x;
typeof ((long) x) y = 0; /* y is a long */
y = 1; /* OK. */
const int x;
typeof ((const long) x) y = 0; /* y is a long */
y = 1; /* OK. */
The wrong behavior is only observed when the unqualified operand type is
equal to the unqualified new type.
This patch makes the semantics of type-casting more consistent and more
correct. All the patch does is to make sure that the FE calls convert()
on the operand of the cast-expression even when the TYPE_MAIN_VARIANT of
the operand type and that of the new type happen to be the same.
Bootstrapped and regtested on x86_64-unknown-linux-gnu. No new testcase
is added because an existing testcase already contains the important
cases; the existing testcase is then adjusted to expect the new correct
behavior. Is this patch OK for trunk?
2014-08-17 Patrick Palka ppa...@gcc.gnu.org
* c-typeck.c (build_c_cast): Do a conversion even when the
TYPE_MAIN_VARIANTs are the same.
2014-08-17 Patrick Palka ppa...@gcc.gnu.org
* gcc.dg/pr13519-1.c: Adjust.
---
gcc/c/c-typeck.c | 2 ++
gcc/testsuite/gcc.dg/pr13519-1.c | 6 +++---
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 0ed92c6..e6745be 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -4947,6 +4947,8 @@ build_c_cast (location_t loc, tree type, tree expr)
|| TREE_CODE (type) == UNION_TYPE)
pedwarn (loc, OPT_Wpedantic,
"ISO C forbids casting nonscalar to the same type");
+
+ value = convert (type, value);
}
else if (TREE_CODE (type) == UNION_TYPE)
{
diff --git a/gcc/testsuite/gcc.dg/pr13519-1.c b/gcc/testsuite/gcc.dg/pr13519-1.c
index 907165f..1117a0e 100644
--- a/gcc/testsuite/gcc.dg/pr13519-1.c
+++ b/gcc/testsuite/gcc.dg/pr13519-1.c
@@ -14,9 +14,9 @@ void fn(void)
{ __typeof__(n) a1; a1=0; }
{ __typeof__(c) a2; a2=0; } /* { dg-error "read-only" "correct error" } */
{ __typeof__((int)n) a3; a3=0; }
- { __typeof__((int)c) a4; a4=0; } /* { dg-bogus "read-only" "bogus error" {
xfail *-*-* } } */
- { __typeof__((const int)n) a5; a5=0; } /* { dg-error "read-only" "correct
error" { xfail *-*-* } } */
- { __typeof__((const int)c) a6; a6=0; } /* { dg-error "read-only" "correct
error" } */
+ { __typeof__((int)c) a4; a4=0; } /* { dg-bogus "read-only" "bogus error" } */
+ { __typeof__((const int)n) a5; a5=0; }
+ { __typeof__((const int)c) a6; a6=0; }
{ __typeof__(0) a7; a7=0; }
{ __typeof__(1) a8; a8=0; }
--
2.1.0
