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c++: Use empty field in constexpr eval. 

In discussion of PR98463, Jakub noted that cxx_fold_indirect_ref_1 was
bailing out early for empty bases even when we do have fields for them (in
C++17 mode or later).  This corrects that.

gcc/cp/ChangeLog:

	* constexpr.c (cxx_fold_indirect_ref_1): Only set *empty_base if we
	don't find a field.
This commit is contained in:
Jason Merrill 2021-01-25 17:02:57 -05:00
parent a0fdff3cf3
commit bc99c54de5
1 changed files with 18 additions and 20 deletions
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38
gcc/cp/constexpr.c
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@ -4734,28 +4734,17 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx, location_t loc, tree type,
{
tree optype = TREE_TYPE (op);
unsigned HOST_WIDE_INT const_nunits;
if (off == 0)
{
if (similar_type_p (optype, type))
return op;
/* Also handle conversion to an empty base class, which
is represented with a NOP_EXPR. */
/* *(foo *)&complexfoo => __real__ complexfoo */
else if (TREE_CODE (optype) == COMPLEX_TYPE
&& similar_type_p (type, TREE_TYPE (optype)))
return build1_loc (loc, REALPART_EXPR, type, op);
}
/* ((foo*)&complexfoo)[1] => __imag__ complexfoo */
if (off == 0 && similar_type_p (optype, type))
return op;
else if (TREE_CODE (optype) == COMPLEX_TYPE
&& similar_type_p (type, TREE_TYPE (optype))
&& tree_to_uhwi (TYPE_SIZE_UNIT (type)) == off)
return build1_loc (loc, IMAGPART_EXPR, type, op);
if (is_empty_class (type)
&& CLASS_TYPE_P (optype)
&& DERIVED_FROM_P (type, optype))
&& similar_type_p (type, TREE_TYPE (optype)))
{
*empty_base = true;
return op;
/* *(foo *)&complexfoo => __real__ complexfoo */
if (off == 0)
return build1_loc (loc, REALPART_EXPR, type, op);
/* ((foo*)&complexfoo)[1] => __imag__ complexfoo */
else if (tree_to_uhwi (TYPE_SIZE_UNIT (type)) == off)
return build1_loc (loc, IMAGPART_EXPR, type, op);
}
/* ((foo*)&vectorfoo)[x] => BIT_FIELD_REF<vectorfoo,...> */
else if (VECTOR_TYPE_P (optype)
@ -4834,6 +4823,15 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx, location_t loc, tree type,
return ret;
}
}
/* Also handle conversion to an empty base class, which
is represented with a NOP_EXPR. */
if (is_empty_class (type)
&& CLASS_TYPE_P (optype)
&& DERIVED_FROM_P (type, optype))
{
*empty_base = true;
return op;
}
}
return NULL_TREE;