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c++: Fix up tsubst of BIT_CAST_EXPR [PR98329] 

As the testcase shows, calling cp_build_bit_cast in tsubst_copy doesn't seem
to be a good idea, because tsubst_copy might not really make the operand
non-dependent, but as processing_template_decl can be 0,
type_dependent_expression_p will return false and then cp_build_bit_cast
assumes the type is non-NULL and non-dependent.
So, this patch just follows what is done e.g. for NOP_EXPR etc. and just
builds some tree in tsubst_copy, and only calls the semantics.c function
from tsubst_copy_and_build.

2021-01-07  Jakub Jelinek  <jakub@redhat.com>

	PR c++/98329
	* pt.c (tsubst_copy) <case BIT_CAST_EXPR>: Don't call
	cp_build_bit_cast here, instead just build_min a BIT_CAST_EXPR and set
	its location.
	(tsubst_copy_and_build): Handle BIT_CAST_EXPR.

	* g++.dg/cpp2a/bit-cast10.C: New test.
This commit is contained in:
Jakub Jelinek 2021-01-07 23:00:28 +01:00
parent 178f0afce3
commit aa4db31dd2
2 changed files with 52 additions and 1 deletions
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11
gcc/cp/pt.c
View File

@ -16796,7 +16796,9 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
{
tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
tree op0 = tsubst_copy (TREE_OPERAND (t, 0), args, complain, in_decl);
return cp_build_bit_cast (EXPR_LOCATION (t), type, op0, complain);
r = build_min (BIT_CAST_EXPR, type, op0);
SET_EXPR_LOCATION (r, EXPR_LOCATION (t));
return r;
}
case SIZEOF_EXPR:
@ -19631,6 +19633,13 @@ tsubst_copy_and_build (tree t,
RETURN (r);
}
case BIT_CAST_EXPR:
{
tree type = tsubst (TREE_TYPE (t), args, complain, in_decl);
tree op0 = RECUR (TREE_OPERAND (t, 0));
RETURN (cp_build_bit_cast (EXPR_LOCATION (t), type, op0, complain));
}
case POSTDECREMENT_EXPR:
case POSTINCREMENT_EXPR:
op1 = tsubst_non_call_postfix_expression (TREE_OPERAND (t, 0),

42
gcc/testsuite/g++.dg/cpp2a/bit-cast10.C Normal file
View File

@ -0,0 +1,42 @@
// PR c++/98329
// { dg-do compile { target c++20 } }
template <typename To, typename From>
constexpr To
foo (const From &from)
{
return __builtin_bit_cast (To, &from);
}
template <typename To, typename From>
constexpr To
bar (const From &from)
{
return __builtin_bit_cast (To, *from);
}
template <typename To, typename From>
constexpr To
baz (const From &from)
{
return __builtin_bit_cast (To, **from);
}
template <typename To, typename From>
constexpr To
qux (const From &from)
{
return __builtin_bit_cast (To, -from);
}
void
test ()
{
int i = 0;
int *j = &i;
int **k = &j;
foo <char *> (i);
bar <int> (j);
baz <int> (k);
qux <int> (i);
}