* [PATCH] Fix cxx_eval_bit_field_ref (PR c++/49136)
@ 2011-05-25 9:04 Jakub Jelinek
0 siblings, 0 replies; only message in thread
From: Jakub Jelinek @ 2011-05-25 9:04 UTC (permalink / raw)
To: gcc-patches
Hi!
optimize_bit_field_compare during folding can create BIT_FIELD_REFs
that reference more than a single bitfield, then mask the right bits from
it. The following patch changes cxx_eval_bit_field_ref to be able to read
the multiple fields from the constructor.
Bootstrapped/regtested on x86_64-linux and i686-linux, acked by Jason in
bugzilla, committed to trunk/4.6.
2011-05-25 Jakub Jelinek <jakub@redhat.com>
PR c++/49136
* semantics.c (cxx_eval_bit_field_ref): Handle the
case when BIT_FIELD_REF doesn't cover only a single field.
* g++.dg/cpp0x/constexpr-bitfield2.C: New test.
* g++.dg/cpp0x/constexpr-bitfield3.C: New test.
--- gcc/cp/semantics.c.jj 2011-05-20 08:14:06.000000000 +0200
+++ gcc/cp/semantics.c 2011-05-24 18:57:00.000000000 +0200
@@ -6442,6 +6442,9 @@ cxx_eval_bit_field_ref (const constexpr_
bool *non_constant_p)
{
tree orig_whole = TREE_OPERAND (t, 0);
+ tree retval, fldval, utype, mask;
+ bool fld_seen = false;
+ HOST_WIDE_INT istart, isize;
tree whole = cxx_eval_constant_expression (call, orig_whole,
allow_non_constant, addr,
non_constant_p);
@@ -6462,12 +6465,47 @@ cxx_eval_bit_field_ref (const constexpr_
return t;
start = TREE_OPERAND (t, 2);
+ istart = tree_low_cst (start, 0);
+ isize = tree_low_cst (TREE_OPERAND (t, 1), 0);
+ utype = TREE_TYPE (t);
+ if (!TYPE_UNSIGNED (utype))
+ utype = build_nonstandard_integer_type (TYPE_PRECISION (utype), 1);
+ retval = build_int_cst (utype, 0);
FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (whole), i, field, value)
{
- if (bit_position (field) == start)
+ tree bitpos = bit_position (field);
+ if (bitpos == start && DECL_SIZE (field) == TREE_OPERAND (t, 1))
return value;
+ if (TREE_CODE (TREE_TYPE (field)) == INTEGER_TYPE
+ && TREE_CODE (value) == INTEGER_CST
+ && host_integerp (bitpos, 0)
+ && host_integerp (DECL_SIZE (field), 0))
+ {
+ HOST_WIDE_INT bit = tree_low_cst (bitpos, 0);
+ HOST_WIDE_INT sz = tree_low_cst (DECL_SIZE (field), 0);
+ HOST_WIDE_INT shift;
+ if (bit >= istart && bit + sz <= istart + isize)
+ {
+ fldval = fold_convert (utype, value);
+ mask = build_int_cst_type (utype, -1);
+ mask = fold_build2 (LSHIFT_EXPR, utype, mask,
+ size_int (TYPE_PRECISION (utype) - sz));
+ mask = fold_build2 (RSHIFT_EXPR, utype, mask,
+ size_int (TYPE_PRECISION (utype) - sz));
+ fldval = fold_build2 (BIT_AND_EXPR, utype, fldval, mask);
+ shift = bit - istart;
+ if (BYTES_BIG_ENDIAN)
+ shift = TYPE_PRECISION (utype) - shift - sz;
+ fldval = fold_build2 (LSHIFT_EXPR, utype, fldval,
+ size_int (shift));
+ retval = fold_build2 (BIT_IOR_EXPR, utype, retval, fldval);
+ fld_seen = true;
+ }
+ }
}
- gcc_unreachable();
+ if (fld_seen)
+ return fold_convert (TREE_TYPE (t), retval);
+ gcc_unreachable ();
return error_mark_node;
}
--- gcc/testsuite/g++.dg/cpp0x/constexpr-bitfield2.C.jj 2011-05-24 14:37:39.000000000 +0200
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-bitfield2.C 2011-05-24 14:36:43.000000000 +0200
@@ -0,0 +1,19 @@
+// PR c++/49136
+// { dg-do compile }
+// { dg-options "-std=c++0x" }
+
+struct day
+{
+ unsigned d : 5;
+ unsigned n : 3;
+ constexpr explicit day (int dd) : d(dd), n(7) {}
+};
+
+struct date {
+ int d;
+ constexpr date (day dd) : d(dd.n != 7 ? 7 : dd.d) {}
+};
+
+constexpr day d(0);
+constexpr date dt(d);
+static_assert (dt.d == 0, "Error");
--- gcc/testsuite/g++.dg/cpp0x/constexpr-bitfield3.C.jj 2011-05-24 14:37:43.000000000 +0200
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-bitfield3.C 2011-05-24 14:43:40.000000000 +0200
@@ -0,0 +1,33 @@
+// PR c++/49136
+// { dg-do compile }
+// { dg-options "-std=c++0x" }
+
+struct S
+{
+ unsigned : 1; unsigned s : 27; unsigned : 4;
+ constexpr S (unsigned int x) : s(x) {}
+};
+
+template <typename S>
+struct T
+{
+ unsigned int t;
+ constexpr T (S s) : t(s.s != 7 ? 0 : s.s) {}
+ constexpr T (S s, S s2) : t(s.s != s2.s ? 0 : s.s) {}
+};
+
+constexpr S s (7), s2 (7);
+constexpr T<S> t (s), t2 (s, s2);
+static_assert (t.t == 7, "Error");
+static_assert (t2.t == 7, "Error");
+
+struct U
+{
+ int a : 1; int s : 1;
+ constexpr U (int x, int y) : a (x), s (y) {}
+};
+
+constexpr U u (0, -1), u2 (-1, -1);
+constexpr T<U> t3 (u), t4 (u, u2);
+static_assert (t3.t == 0, "Error");
+static_assert (t4.t == -1, "Error");
Jakub
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