Hi!
We claim we support P0415R1 (constexpr complex), but e.g.
#include <complex>
constexpr bool
foo ()
{
std::complex<double> a (1.0, 2.0);
a += 3.0;
a.real (6.0);
return a.real () == 6.0 && a.imag () == 2.0;
}
static_assert (foo ());
fails with
test.C:12:20: error: non-constant condition for static assertion
12 | static_assert (foo ());
| ~~~~^~
test.C:12:20: in ‘constexpr’ expansion of ‘foo()’
test.C:8:10: in ‘constexpr’ expansion of
‘a.std::complex<double>::real(6.0e+0)’
test.C:12:20: error: modification of ‘__real__
a.std::complex<double>::_M_value’ is not a constant expression
The problem is we don't handle REALPART_EXPR and IMAGPART_EXPR
in cxx_eval_store_expression.
The following patch attempts to support it (with a requirement
that those are the outermost expressions, ARRAY_REF/COMPONENT_REF
etc. are just not possible on the result of these, BIT_FIELD_REF
would be theoretically possible if trying to extract some bits
from one part of a complex int, but I don't see how it could appear
in the FE trees.
For these references, the code handles value being COMPLEX_CST,
COMPLEX_EXPR or CONSTRUCTOR_NO_CLEARING empty CONSTRUCTOR (what we use
to represent uninitialized values for C++20 and later) and the
code starts by rewriting it to COMPLEX_EXPR, so that we can freely
adjust the individual parts and later on possibly optimize it back
to COMPLEX_CST if both halves are constant.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2022-06-09 Jakub Jelinek <ja...@redhat.com>
PR c++/88174
* constexpr.cc (cxx_eval_store_expression): Handle REALPART_EXPR
and IMAGPART_EXPR.
* g++.dg/cpp1y/constexpr-complex1.C: New test.
--- gcc/cp/constexpr.cc.jj 2022-06-08 08:21:02.973448193 +0200
+++ gcc/cp/constexpr.cc 2022-06-08 17:13:04.986040449 +0200
@@ -5707,6 +5707,20 @@ cxx_eval_store_expression (const constex
}
break;
+ case REALPART_EXPR:
+ gcc_assert (probe == target);
+ vec_safe_push (refs, integer_zero_node);
+ vec_safe_push (refs, TREE_TYPE (probe));
+ probe = TREE_OPERAND (probe, 0);
+ break;
+
+ case IMAGPART_EXPR:
+ gcc_assert (probe == target);
+ vec_safe_push (refs, integer_one_node);
+ vec_safe_push (refs, TREE_TYPE (probe));
+ probe = TREE_OPERAND (probe, 0);
+ break;
+
default:
if (evaluated)
object = probe;
@@ -5749,6 +5763,8 @@ cxx_eval_store_expression (const constex
auto_vec<int> index_pos_hints;
bool activated_union_member_p = false;
bool empty_base = false;
+ int complex_part = -1;
+ tree *complex_expr = NULL;
while (!refs->is_empty ())
{
if (*valp == NULL_TREE)
@@ -5785,14 +5801,36 @@ cxx_eval_store_expression (const constex
*valp = ary_ctor;
}
- /* If the value of object is already zero-initialized, any new ctors for
- subobjects will also be zero-initialized. */
- no_zero_init = CONSTRUCTOR_NO_CLEARING (*valp);
-
enum tree_code code = TREE_CODE (type);
tree reftype = refs->pop();
tree index = refs->pop();
+ if (code == COMPLEX_TYPE)
+ {
+ if (TREE_CODE (*valp) == COMPLEX_CST)
+ *valp = build2 (COMPLEX_EXPR, type, TREE_REALPART (*valp),
+ TREE_IMAGPART (*valp));
+ else if (TREE_CODE (*valp) == CONSTRUCTOR
+ && CONSTRUCTOR_NELTS (*valp) == 0
+ && CONSTRUCTOR_NO_CLEARING (*valp))
+ {
+ tree r = build_constructor (reftype, NULL);
+ CONSTRUCTOR_NO_CLEARING (r) = 1;
+ *valp = build2 (COMPLEX_EXPR, type, r, r);
+ }
+ gcc_assert (TREE_CODE (*valp) == COMPLEX_EXPR);
+ complex_expr = valp;
+ valp = &TREE_OPERAND (*valp, index != integer_zero_node);
+ gcc_checking_assert (refs->is_empty ());
+ type = reftype;
+ complex_part = index != integer_zero_node;
+ break;
+ }
+
+ /* If the value of object is already zero-initialized, any new ctors for
+ subobjects will also be zero-initialized. */
+ no_zero_init = CONSTRUCTOR_NO_CLEARING (*valp);
+
if (code == RECORD_TYPE && is_empty_field (index))
/* Don't build a sub-CONSTRUCTOR for an empty base or field, as they
have no data and might have an offset lower than previously declared
@@ -5946,6 +5984,24 @@ cxx_eval_store_expression (const constex
= get_or_insert_ctor_field (*valp, indexes[i], index_pos_hints[i]);
valp = &cep->value;
}
+ if (complex_part != -1)
+ {
+ if (TREE_CODE (*valp) == COMPLEX_CST)
+ *valp = build2 (COMPLEX_EXPR, TREE_TYPE (*valp),
+ TREE_REALPART (*valp),
+ TREE_IMAGPART (*valp));
+ else if (TREE_CODE (*valp) == CONSTRUCTOR
+ && CONSTRUCTOR_NELTS (*valp) == 0
+ && CONSTRUCTOR_NO_CLEARING (*valp))
+ {
+ tree r = build_constructor (TREE_TYPE (TREE_TYPE (*valp)), NULL);
+ CONSTRUCTOR_NO_CLEARING (r) = 1;
+ *valp = build2 (COMPLEX_EXPR, TREE_TYPE (*valp), r, r);
+ }
+ gcc_assert (TREE_CODE (*valp) == COMPLEX_EXPR);
+ complex_expr = valp;
+ valp = &TREE_OPERAND (*valp, complex_part);
+ }
}
if (*non_constant_p)
@@ -6016,6 +6072,22 @@ cxx_eval_store_expression (const constex
if (TREE_CODE (TREE_TYPE (elt)) == UNION_TYPE)
CONSTRUCTOR_NO_CLEARING (elt) = false;
}
+ if (complex_expr)
+ {
+ if (tree c = const_binop (COMPLEX_EXPR, TREE_TYPE (*complex_expr),
+ TREE_OPERAND (*complex_expr, 0),
+ TREE_OPERAND (*complex_expr, 1)))
+ *complex_expr = c;
+ else
+ {
+ TREE_CONSTANT (*complex_expr)
+ = (TREE_CONSTANT (TREE_OPERAND (*complex_expr, 0))
+ & TREE_CONSTANT (TREE_OPERAND (*complex_expr, 1)));
+ TREE_SIDE_EFFECTS (*complex_expr)
+ = (TREE_SIDE_EFFECTS (TREE_OPERAND (*complex_expr, 0))
+ | TREE_SIDE_EFFECTS (TREE_OPERAND (*complex_expr, 1)));
+ }
+ }
if (lval)
return target;
--- gcc/testsuite/g++.dg/cpp1y/constexpr-complex1.C.jj 2022-06-08
17:32:39.190148964 +0200
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-complex1.C 2022-06-08
17:29:04.413321741 +0200
@@ -0,0 +1,24 @@
+// PR c++/88174
+// { dg-do compile { target c++14 } }
+
+constexpr bool
+foo (double x, double y, double z, double w)
+{
+ __complex__ double a = 0;
+ __real__ a = x;
+ __imag__ a = y;
+#if __cpp_constexpr >= 201907L
+ __complex__ double b;
+ __real__ b = z;
+#else
+ __complex__ double b = z;
+#endif
+ __imag__ b = w;
+ a += b;
+ a -= b;
+ a *= b;
+ a /= b;
+ return __real__ a == x && __imag__ a == y;
+}
+
+static_assert (foo (1.0, 2.0, 3.0, 4.0), "");
Jakub
