Hi!
While in C++11, builtins returning two results, one of them by dereferencing
a pointer argument can't be constexpr, in my understanding in C++14
generalized constexprs they can.
So, this patch tweaks cxx_eval_builtin_function_call so that it handles how
builtins.c folds these builtins (i.e. COMPOUND_EXPR with first operand
being *arg = const1 and second operand const2, optionally all wrapped into a
NON_LVALUE_EXPR.
In addition, I've noticed that the lval argument is passed down to
evaluation of arguments, that doesn't make sense to me, IMHO arguments
should be always evakyated as rvalues (and for non-builtins they are).
sincos (which has stores 2 results through pointers) is folded earlier into
cexpi and thus worked already before.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2016-07-15 Jakub Jelinek <ja...@redhat.com>
PR c++/50060
* constexpr.c (cxx_eval_builtin_function_call): Pass false as lval
when evaluating call arguments, make the lval argument nameless. For
C++14 and later, if new_call is COMPOUND_EXPR with a assignment and
constant, evaluate the assignment and return the constant.
* g++.dg/cpp1y/constexpr-50060.C: New test.
--- gcc/cp/constexpr.c.jj 2016-07-11 22:18:01.000000000 +0200
+++ gcc/cp/constexpr.c 2016-07-15 15:27:50.820085561 +0200
@@ -1078,8 +1078,7 @@ get_nth_callarg (tree t, int n)
static tree
cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
- bool lval,
- bool *non_constant_p, bool *overflow_p)
+ bool, bool *non_constant_p, bool *overflow_p)
{
const int nargs = call_expr_nargs (t);
tree *args = (tree *) alloca (nargs * sizeof (tree));
@@ -1105,7 +1104,7 @@ cxx_eval_builtin_function_call (const co
for (i = 0; i < nargs; ++i)
{
args[i] = cxx_eval_constant_expression (&new_ctx, CALL_EXPR_ARG (t, i),
- lval, &dummy1, &dummy2);
+ false, &dummy1, &dummy2);
if (bi_const_p)
/* For __built_in_constant_p, fold all expressions with constant values
even if they aren't C++ constant-expressions. */
@@ -1119,6 +1118,27 @@ cxx_eval_builtin_function_call (const co
/* Fold away the NOP_EXPR from fold_builtin_n. */
new_call = fold (new_call);
force_folding_builtin_constant_p = save_ffbcp;
+
+ if (cxx_dialect >= cxx14)
+ {
+ tree r = new_call;
+ if (TREE_CODE (r) == NON_LVALUE_EXPR)
+ r = TREE_OPERAND (r, 0);
+ if (TREE_CODE (r) == COMPOUND_EXPR
+ && TREE_CODE (TREE_OPERAND (r, 0)) == MODIFY_EXPR
+ && reduced_constant_expression_p (TREE_OPERAND (TREE_OPERAND (r, 0),
+ 1)))
+ {
+ /* The frexp, modf, remquo and lgamma_r builtins (and their variants)
+ with &var as last argument are folded into
+ (var = const1), const2, sometimes wrapped into
+ NON_LVALUE_EXPR. */
+ cxx_eval_constant_expression (&new_ctx, TREE_OPERAND (r, 0),
+ false, non_constant_p, overflow_p);
+ new_call = TREE_OPERAND (r, 1);
+ }
+ }
+
VERIFY_CONSTANT (new_call);
return new_call;
}
--- gcc/testsuite/g++.dg/cpp1y/constexpr-50060.C.jj 2016-07-15
15:34:12.469124944 +0200
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-50060.C 2016-07-15
15:59:36.285303078 +0200
@@ -0,0 +1,100 @@
+// PR c++/50060
+// { dg-do compile { target c++14 } }
+
+// sincos and lgamma_r aren't available in -std=c++14,
+// only in -std=gnu++14. Use __builtin_* in that case.
+extern "C" void sincos (double, double *, double *);
+extern "C" double frexp (double, int *);
+extern "C" double modf (double, double *);
+extern "C" double remquo (double, double, int *);
+extern "C" double lgamma_r (double, int *);
+
+constexpr double
+f0 (double x)
+{
+ double y {};
+ double z {};
+ __builtin_sincos (x, &y, &z);
+ return y;
+}
+
+constexpr double
+f1 (double x)
+{
+ double y {};
+ double z {};
+ __builtin_sincos (x, &y, &z);
+ return z;
+}
+
+constexpr double
+f2 (double x)
+{
+ int y {};
+ return frexp (x, &y);
+}
+
+constexpr int
+f3 (double x)
+{
+ int y {};
+ frexp (x, &y);
+ return y;
+}
+
+constexpr double
+f4 (double x)
+{
+ double y {};
+ return modf (x, &y);
+}
+
+constexpr double
+f5 (double x)
+{
+ double y {};
+ modf (x, &y);
+ return y;
+}
+
+constexpr double
+f6 (double x, double y)
+{
+ int z {};
+ return remquo (x, y, &z);
+}
+
+constexpr int
+f7 (double x, double y)
+{
+ int z {};
+ remquo (x, y, &z);
+ return z;
+}
+
+constexpr double
+f8 (double x)
+{
+ int y {};
+ return __builtin_lgamma_r (x, &y);
+}
+
+constexpr int
+f9 (double x)
+{
+ int y {};
+ __builtin_lgamma_r (x, &y);
+ return y;
+}
+
+static_assert (f0 (0.0) == 0.0, "");
+static_assert (f1 (0.0) == 1.0, "");
+static_assert (f2 (6.5) == 0.8125, "");
+static_assert (f3 (6.5) == 3, "");
+static_assert (f4 (-7.25) == -0.25, "");
+static_assert (f5 (-7.25) == -7.0, "");
+static_assert (f6 (3.0, 2.0) == -1.0, "");
+static_assert (f7 (3.0, 2.0) == 2, "");
+static_assert (f8 (0.75) >= 0.20 && f8 (0.75) <= 0.21, "");
+static_assert (f8 (0.75) >= 0.20 && f8 (0.75) <= 0.21, "");
+static_assert (f9 (0.75) == 1, "");
Jakub
