fold-const: Handle bitfields in native_encode_initializer [PR93121]

When working on __builtin_bit_cast that needs to handle bitfields too,
I've made the following change to handle at least some bitfields in
native_encode_initializer (those that have integral representative).

2020-07-20  Jakub Jelinek  <jakub@redhat.com>

	PR libstdc++/93121
	* fold-const.c (native_encode_initializer): Handle bit-fields.

	* gcc.dg/tree-ssa/pr93121-1.c: New test.

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 67a379f..cfae846 100644 (file)
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -8047,6 +8047,7 @@ native_encode_initializer (tree init, unsigned char *ptr, int len,
              tree field = ce->index;
              tree val = ce->value;
              HOST_WIDE_INT pos, fieldsize;
+             unsigned HOST_WIDE_INT bpos = 0, epos = 0;
 
              if (field == NULL_TREE)
                return 0;
@@ -8066,15 +8067,122 @@ native_encode_initializer (tree init, unsigned char *ptr, int len,
              if (fieldsize == 0)
                continue;
 
+             if (DECL_BIT_FIELD (field))
+               {
+                 if (!tree_fits_uhwi_p (DECL_FIELD_BIT_OFFSET (field)))
+                   return 0;
+                 fieldsize = TYPE_PRECISION (TREE_TYPE (field));
+                 bpos = tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field));
+                 if (bpos % BITS_PER_UNIT)
+                   bpos %= BITS_PER_UNIT;
+                 else
+                   bpos = 0;
+                 fieldsize += bpos;
+                 epos = fieldsize % BITS_PER_UNIT;
+                 fieldsize += BITS_PER_UNIT - 1;
+                 fieldsize /= BITS_PER_UNIT;
+               }
+
              if (off != -1 && pos + fieldsize <= off)
                continue;
 
-             if (DECL_BIT_FIELD (field))
-               return 0;
-
              if (val == NULL_TREE)
                continue;
 
+             if (DECL_BIT_FIELD (field))
+               {
+                 /* FIXME: Handle PDP endian.  */
+                 if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)
+                   return 0;
+
+                 tree repr = DECL_BIT_FIELD_REPRESENTATIVE (field);
+                 if (repr == NULL_TREE
+                     || TREE_CODE (val) != INTEGER_CST
+                     || !INTEGRAL_TYPE_P (TREE_TYPE (repr)))
+                   return 0;
+
+                 HOST_WIDE_INT rpos = int_byte_position (repr);
+                 if (rpos > pos)
+                   return 0;
+                 wide_int w = wi::to_wide (val,
+                                           TYPE_PRECISION (TREE_TYPE (repr)));
+                 int diff = (TYPE_PRECISION (TREE_TYPE (repr))
+                             - TYPE_PRECISION (TREE_TYPE (field)));
+                 HOST_WIDE_INT bitoff = (pos - rpos) * BITS_PER_UNIT + bpos;
+                 if (!BYTES_BIG_ENDIAN)
+                   w = wi::lshift (w, bitoff);
+                 else
+                   w = wi::lshift (w, diff - bitoff);
+                 val = wide_int_to_tree (TREE_TYPE (repr), w);
+
+                 unsigned char buf[MAX_BITSIZE_MODE_ANY_INT
+                                   / BITS_PER_UNIT + 1];
+                 int l = native_encode_int (val, buf, sizeof buf, 0);
+                 if (l * BITS_PER_UNIT != TYPE_PRECISION (TREE_TYPE (repr)))
+                   return 0;
+
+                 if (ptr == NULL)
+                   continue;
+
+                 /* If the bitfield does not start at byte boundary, handle
+                    the partial byte at the start.  */
+                 if (bpos
+                     && (off == -1 || (pos >= off && len >= 1)))
+                   {
+                     if (!BYTES_BIG_ENDIAN)
+                       {
+                         int mask = (1 << bpos) - 1;
+                         buf[pos - rpos] &= ~mask;
+                         buf[pos - rpos] |= ptr[pos - o] & mask;
+                       }
+                     else
+                       {
+                         int mask = (1 << (BITS_PER_UNIT - bpos)) - 1;
+                         buf[pos - rpos] &= mask;
+                         buf[pos - rpos] |= ptr[pos - o] & ~mask;
+                       }
+                   }
+                 /* If the bitfield does not end at byte boundary, handle
+                    the partial byte at the end.  */
+                 if (epos
+                     && (off == -1
+                         || pos + fieldsize <= (HOST_WIDE_INT) off + len))
+                   {
+                     if (!BYTES_BIG_ENDIAN)
+                       {
+                         int mask = (1 << epos) - 1;
+                         buf[pos - rpos + fieldsize - 1] &= mask;
+                         buf[pos - rpos + fieldsize - 1]
+                           |= ptr[pos + fieldsize - 1 - o] & ~mask;
+                       }
+                      else
+                       {
+                         int mask = (1 << (BITS_PER_UNIT - epos)) - 1;
+                         buf[pos - rpos + fieldsize - 1] &= ~mask;
+                         buf[pos - rpos + fieldsize - 1]
+                           |= ptr[pos + fieldsize - 1 - o] & mask;
+                       }
+                   }
+                 if (off == -1
+                     || (pos >= off
+                         && (pos + fieldsize <= (HOST_WIDE_INT) off + len)))
+                   memcpy (ptr + pos - o, buf + (pos - rpos), fieldsize);
+                 else
+                   {
+                     /* Partial overlap.  */
+                     HOST_WIDE_INT fsz = fieldsize;
+                     if (pos < off)
+                       {
+                         fsz -= (off - pos);
+                         pos = off;
+                       }
+                     if (pos + fsz > (HOST_WIDE_INT) off + len)
+                       fsz = (HOST_WIDE_INT) off + len - pos;
+                     memcpy (ptr + pos - off, buf + (pos - rpos), fsz);
+                   }
+                 continue;
+               }
+
              if (off == -1
                  || (pos >= off
                      && (pos + fieldsize <= (HOST_WIDE_INT) off + len)))

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr93121-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr93121-1.c
new file mode 100644 (file)
index 0000000..4bf40c1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr93121-1.c
@@ -0,0 +1,56 @@
+/* PR libstdc++/93121 */
+/* { dg-do compile { target { ilp32 || lp64 } } } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+union U { int a[3]; short c[6]; struct S { int d; int a : 2; int f : 1; int b : 24; int c : 5; int e; } b; };
+const union U u = { .b = { 0x7efa3412, 3, 0, 0x50eca8, 0xb, 0x1eeffeed } };
+const union U v = { .b = { 0x7efa3412, 1, 1, 0x7feedb, 0x5, 0x1eeffeed } };
+union W { struct T { long long int a, b : 11, c : 3, d : 37, e : 1, f : 10, g : 2, h; } a; int b[6]; short c[12]; long long d[3]; };
+const union W w = { .a = { 0x0feedbacdeadbeefLL, -1011, 2, -0xbacdeadbeLL, -1, 721, 1, 0x0feedbacdeadbeefLL } };
+int a, b, c, d, e, f, g, h, i, j, k, l;
+long long m;
+
+void
+foo ()
+{
+  a = u.a[1];
+  b = v.a[1];
+  c = u.c[2];
+  d = u.c[3];
+  e = v.c[2];
+  f = v.c[3];
+  g = w.b[2];
+  h = w.b[3];
+  i = w.c[4];
+  j = w.c[5];
+  k = w.c[6];
+  l = w.c[7];
+  m = w.d[1];
+}
+
+/* { dg-final { scan-tree-dump-times "a = 1518822723;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "b = 738162397;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "c = 25923;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "d = 23175;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "e = 30429;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "f = 11263;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "g = 1418761229;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "h = 1830622408;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "i = -27635;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "j = 21648;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "k = 5320;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "l = 27933;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "m = 7862463375103529997;" 1 "optimized" { target le } } } */
+/* { dg-final { scan-tree-dump-times "a = -904030965;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "b = 1878907749;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "c = -13795;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "d = -27381;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "e = 28669;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "f = -9371;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "g = -2119529884;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "h = 709385029;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "i = -32342;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "j = -30108;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "k = 10824;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "l = 23365;" 1 "optimized" { target be } } } */
+/* { dg-final { scan-tree-dump-times "m = -9103311533965288635;" 1 "optimized" { target be } } } */