wide-int.h has
/* For fixed-precision integers like offset_int and widest_int,
handle the case where the shift value is constant and the
result is a single nonnegative HWI (meaning that we don't
need to worry about val[1]). This is particularly common
for converting a byte count to a bit count.
For variable-precision integers like wide_int, handle HWI
and sub-HWI integers inline. */
if (__builtin_constant_p (xi.precision > HOST_BITS_PER_WIDE_INT)
? (__builtin_constant_p (shift < HOST_BITS_PER_WIDE_INT - 1)
&& xi.len == 1
&& xi.val[0] <= (HOST_WIDE_INT) ((unsigned HOST_WIDE_INT)
HOST_WIDE_INT_MAX >>
shift))
: precision <= HOST_BITS_PER_WIDE_INT)
{
val[0] = xi.ulow () << shift;
result.set_len (1);
}
__builtin_constant_p is miscompiled due to PR c++/65656, which leads
to PR 69399. Backport the PR c++/65656 fix to gcc-5-branch fixes
PR 69399. OK for gcc-5-branch if there is no regression on x86-64?
Thanks.
H.J.
--
We have two desires for interaction of __builtin_constant_p with
constexpr: 1) it should be a constant-expression even if its operands
are not, and 2) we shouldn't fold it to false prematurely when parsing a
constexpr function (c++/54021). We were having trouble with both of
these, and this patch fixes #1 without breaking #2.
gcc/cp/
Backport from mainline
2015-04-28 Jason Merrill <ja...@redhat.com>
PR c++/65656
* constexpr.c (cxx_eval_builtin_function_call): Fix
__builtin_constant_p.
gcc/testsuite/
Backport from mainline
2015-04-28 Jason Merrill <ja...@redhat.com>
PR c++/65656
* g++.dg/cpp0x/constexpr-builtin3.C: New test.
---
gcc/cp/constexpr.c | 32 +++++++++++++++++--------
gcc/testsuite/g++.dg/cpp0x/constexpr-builtin3.C | 6 +++++
2 files changed, 28 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-builtin3.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 4ca99e8..3c9362e 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1024,7 +1024,7 @@ lookup_parameter_binding (const constexpr_call *call,
tree t)
represented by _CST nodes. */
static tree
-cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t,
+cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
bool lval,
bool *non_constant_p, bool *overflow_p)
{
@@ -1032,18 +1032,30 @@ cxx_eval_builtin_function_call (const constexpr_ctx
*ctx, tree t,
tree *args = (tree *) alloca (nargs * sizeof (tree));
tree new_call;
int i;
- for (i = 0; i < nargs; ++i)
+
+ /* Don't fold __builtin_constant_p within a constexpr function. */
+ if (DECL_FUNCTION_CODE (fun) == BUILT_IN_CONSTANT_P
+ && current_function_decl
+ && DECL_DECLARED_CONSTEXPR_P (current_function_decl))
{
- args[i] = cxx_eval_constant_expression (ctx, CALL_EXPR_ARG (t, i),
- lval,
- non_constant_p, overflow_p);
- if (ctx->quiet && *non_constant_p)
- return t;
+ *non_constant_p = true;
+ return t;
}
- if (*non_constant_p)
- return t;
+
+ /* Be permissive for arguments to built-ins; __builtin_constant_p should
+ return constant false for a non-constant argument. */
+ constexpr_ctx new_ctx = *ctx;
+ new_ctx.quiet = true;
+ bool dummy1 = false, dummy2 = false;
+ for (i = 0; i < nargs; ++i)
+ args[i] = cxx_eval_constant_expression (&new_ctx, CALL_EXPR_ARG (t, i),
+ lval, &dummy1, &dummy2);
+
+ bool save_ffbcp = force_folding_builtin_constant_p;
+ force_folding_builtin_constant_p = true;
new_call = fold_build_call_array_loc (EXPR_LOCATION (t), TREE_TYPE (t),
CALL_EXPR_FN (t), nargs, args);
+ force_folding_builtin_constant_p = save_ffbcp;
VERIFY_CONSTANT (new_call);
return new_call;
}
@@ -1226,7 +1238,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
return void_node;
if (is_builtin_fn (fun))
- return cxx_eval_builtin_function_call (ctx, t,
+ return cxx_eval_builtin_function_call (ctx, t, fun,
lval, non_constant_p, overflow_p);
if (!DECL_DECLARED_CONSTEXPR_P (fun))
{
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-builtin3.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-builtin3.C
new file mode 100644
index 0000000..3582525
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-builtin3.C
@@ -0,0 +1,6 @@
+// PR c++/65656
+// { dg-options "-std=c++11 -O" }
+
+int main(int argc, char *argv[]) {
+ constexpr bool x = __builtin_constant_p(argc);
+}
--
2.5.0
