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c++: Fix for decltype and bit-fields [PR95009]

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Here, decltype deduces the wrong type for certain expressions involving
bit-fields.  Unlike in C, in C++ bit-field width is explicitly not part
of the type, so I think decltype should never deduce to 'int:N'.  The
problem isn't that we're not calling unlowered_expr_type--we are--it's
that is_bitfield_expr_with_lowered_type only handles certain codes, but
not others.  For example, += works fine but ++ does not.

This also fixes decltype-bitfield2.C where we were crashing (!), but
unfortunately it does not fix 84516 or 70733 where the problem is likely
a missing call to unlowered_expr_type.  It occurs to me now that typeof
likely has had the same issue, but this patch should fix that too.

	PR c++/95009

gcc/cp/ChangeLog:

	* typeck.c (is_bitfield_expr_with_lowered_type) <case MODIFY_EXPR>:
	Handle UNARY_PLUS_EXPR, NEGATE_EXPR, NON_LVALUE_EXPR, BIT_NOT_EXPR,
	P*CREMENT_EXPR too.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/decltype-bitfield1.C: New test.
	* g++.dg/cpp0x/decltype-bitfield2.C: New test.
This commit is contained in:
Marek Polacek 2021-12-04 12:07:41 -05:00
parent 7ef68c37b3
commit 3a2257e6b3
3 changed files with 94 additions and 3 deletions
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14
gcc/cp/typeck.c
View file

@ -2209,9 +2209,9 @@ invalid_nonstatic_memfn_p (location_t loc, tree expr, tsubst_flags_t complain)
return false;
}
/* If EXP is a reference to a bitfield, and the type of EXP does not
match the declared type of the bitfield, return the declared type
of the bitfield. Otherwise, return NULL_TREE. */
/* If EXP is a reference to a bit-field, and the type of EXP does not
match the declared type of the bit-field, return the declared type
of the bit-field. Otherwise, return NULL_TREE. */
tree
is_bitfield_expr_with_lowered_type (const_tree exp)
@ -2230,6 +2230,14 @@ is_bitfield_expr_with_lowered_type (const_tree exp)
case MODIFY_EXPR:
case SAVE_EXPR:
case UNARY_PLUS_EXPR:
case PREDECREMENT_EXPR:
case PREINCREMENT_EXPR:
case POSTDECREMENT_EXPR:
case POSTINCREMENT_EXPR:
case NEGATE_EXPR:
case NON_LVALUE_EXPR:
case BIT_NOT_EXPR:
return is_bitfield_expr_with_lowered_type (TREE_OPERAND (exp, 0));
case COMPONENT_REF:

65
gcc/testsuite/g++.dg/cpp0x/decltype-bitfield1.C Normal file
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@ -0,0 +1,65 @@
// PR c++/95009
// { dg-do compile { target c++11 } }
struct false_type { static constexpr bool value = false; };
struct true_type { static constexpr bool value = true; };
template<class T, class U>
struct is_same : false_type {};
template<class T>
struct is_same<T, T> : true_type {};
struct A {
int i : 31;
unsigned long l : 37;
} a;
void
g ()
{
// Careful: pre{in,de}crements are lvalues -> deduce T&. */
static_assert (is_same<decltype(a.i), int>::value, "");
static_assert (is_same<decltype((a.i)), int&>::value, "");
static_assert (is_same<decltype(++a.i), int&>::value, "");
static_assert (is_same<decltype((++a.i)), int&>::value, "");
static_assert (is_same<decltype(a.i++), int>::value, "");
static_assert (is_same<decltype((a.i++)), int>::value, "");
static_assert (is_same<decltype(--a.i), int&>::value, "");
static_assert (is_same<decltype((--a.i)), int&>::value, "");
static_assert (is_same<decltype(a.i--), int>::value, "");
static_assert (is_same<decltype((a.i--)), int>::value, "");
static_assert (is_same<decltype(a.i += 1), int&>::value, "");
static_assert (is_same<decltype((a.i += 1)), int&>::value, "");
static_assert (is_same<decltype(a.i -= 1), int&>::value, "");
static_assert (is_same<decltype((a.i -= 1)), int&>::value, "");
static_assert (is_same<decltype(a.i *= 1), int&>::value, "");
static_assert (is_same<decltype((a.i *= 1)), int&>::value, "");
static_assert (is_same<decltype(+a.i), int>::value, "");
static_assert (is_same<decltype((+a.i)), int>::value, "");
static_assert (is_same<decltype(-a.i), int>::value, "");
static_assert (is_same<decltype((-a.i)), int>::value, "");
static_assert (is_same<decltype(~a.i), int>::value, "");
static_assert (is_same<decltype((~a.i)), int>::value, "");
static_assert (is_same<decltype(a.l), unsigned long>::value, "");
static_assert (is_same<decltype((a.l)), unsigned long&>::value, "");
static_assert (is_same<decltype(++a.l), unsigned long&>::value, "");
static_assert (is_same<decltype((++a.l)), unsigned long&>::value, "");
static_assert (is_same<decltype(a.l++), unsigned long>::value, "");
static_assert (is_same<decltype((a.l++)), unsigned long>::value, "");
static_assert (is_same<decltype(--a.l), unsigned long&>::value, "");
static_assert (is_same<decltype((--a.l)), unsigned long&>::value, "");
static_assert (is_same<decltype(a.l--), unsigned long>::value, "");
static_assert (is_same<decltype((a.l--)), unsigned long>::value, "");
static_assert (is_same<decltype(a.l += 1), unsigned long&>::value, "");
static_assert (is_same<decltype((a.l += 1)), unsigned long&>::value, "");
static_assert (is_same<decltype(a.l -= 1), unsigned long&>::value, "");
static_assert (is_same<decltype((a.l -= 1)), unsigned long&>::value, "");
static_assert (is_same<decltype(a.l *= 1), unsigned long&>::value, "");
static_assert (is_same<decltype((a.l *= 1)), unsigned long&>::value, "");
static_assert (is_same<decltype(+a.l), unsigned long>::value, "");
static_assert (is_same<decltype((+a.l)), unsigned long>::value, "");
static_assert (is_same<decltype(-a.l), unsigned long>::value, "");
static_assert (is_same<decltype((-a.l)), unsigned long>::value, "");
static_assert (is_same<decltype(~a.l), unsigned long>::value, "");
static_assert (is_same<decltype((~a.l)), unsigned long>::value, "");
}

18
gcc/testsuite/g++.dg/cpp0x/decltype-bitfield2.C Normal file
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@ -0,0 +1,18 @@
// PR c++/95009
// { dg-do compile { target c++11 } }
struct A {
int i:31;
};
template<typename>
void f ()
{
}
int main ()
{
A a;
f<decltype(a.i += 1)>();
f<decltype(++a.i)>();
}