Use a single comparison for index-based alias checks
authorRichard Sandiford <richard.sandiford@arm.com>
Sat, 16 Nov 2019 11:43:31 +0000 (11:43 +0000)
committerRichard Sandiford <rsandifo@gcc.gnu.org>
Sat, 16 Nov 2019 11:43:31 +0000 (11:43 +0000)
This patch rewrites the index-based alias checks to use conditions
of the form:

  (unsigned T) (a - b + bias) <= limit

E.g. before the patch:

  struct s { int x[100]; };

  void
  f1 (struct s *s1, int a, int b)
  {
    for (int i = 0; i < 32; ++i)
      s1->x[i + a] += s1->x[i + b];
  }

used:

        add     w3, w1, 3
        cmp     w3, w2
        add     w3, w2, 3
        ccmp    w1, w3, 0, ge
        ble     .L2

whereas after the patch it uses:

        sub     w3, w1, w2
        add     w3, w3, 3
        cmp     w3, 6
        bls     .L2

The patch also fixes the seg_len1 and seg_len2 negation for cases in
which seg_len is a "negative unsigned" value narrower than 64 bits,
like it is for 32-bit targets.  Previously we'd end up with values
like 0xffffffff000000001 instead of 1.

2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
* tree-data-ref.c (create_intersect_range_checks_index): Rewrite
the index tests to have the form (unsigned T) (B - A + bias) <= limit.

gcc/testsuite/
* gcc.dg/vect/vect-alias-check-18.c: New test.
* gcc.dg/vect/vect-alias-check-19.c: Likewise.
* gcc.dg/vect/vect-alias-check-20.c: Likewise.

From-SVN: r278354

gcc/ChangeLog
gcc/testsuite/ChangeLog
gcc/testsuite/gcc.dg/vect/vect-alias-check-18.c [new file with mode: 0644]
gcc/testsuite/gcc.dg/vect/vect-alias-check-19.c [new file with mode: 0644]
gcc/testsuite/gcc.dg/vect/vect-alias-check-20.c [new file with mode: 0644]
gcc/tree-data-ref.c

index c194a0aa58c597379da72ffb88ac3f72e4486d99..e99cfe70d1018c9c85d0b2b7c5a640444de21ef3 100644 (file)
@@ -1,3 +1,8 @@
+2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>
+
+       * tree-data-ref.c (create_intersect_range_checks_index): Rewrite
+       the index tests to have the form (unsigned T) (B - A + bias) <= limit.
+
 2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>
 
        * tree-data-ref.c (create_intersect_range_checks_index)
index c701507ec3e7001bc7b97523673c19caf8bf734c..ef5bd71af8e9b3617cd2e14386644a496179a03b 100644 (file)
@@ -1,3 +1,9 @@
+2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>
+
+       * gcc.dg/vect/vect-alias-check-18.c: New test.
+       * gcc.dg/vect/vect-alias-check-19.c: Likewise.
+       * gcc.dg/vect/vect-alias-check-20.c: Likewise.
+
 2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>
 
        * gcc.dg/vect/vect-alias-check-1.c: Test for the type of alias check.
diff --git a/gcc/testsuite/gcc.dg/vect/vect-alias-check-18.c b/gcc/testsuite/gcc.dg/vect/vect-alias-check-18.c
new file mode 100644 (file)
index 0000000..e9fd31a
--- /dev/null
@@ -0,0 +1,64 @@
+#define N 200
+#define DIST 32
+
+typedef signed char sc;
+typedef unsigned char uc;
+typedef signed short ss;
+typedef unsigned short us;
+typedef int si;
+typedef unsigned int ui;
+typedef signed long long sll;
+typedef unsigned long long ull;
+
+#define FOR_EACH_TYPE(M) \
+  M (sc) M (uc) \
+  M (ss) M (us) \
+  M (si) M (ui) \
+  M (sll) M (ull) \
+  M (float) M (double)
+
+#define TEST_VALUE(I) ((I) * 11 / 2)
+
+#define ADD_TEST(TYPE)                         \
+  TYPE a_##TYPE[N * 2];                                \
+  void __attribute__((noinline, noclone))      \
+  test_##TYPE (int x, int y)                   \
+  {                                            \
+    for (int i = 0; i < N; ++i)                        \
+      a_##TYPE[x - i] += a_##TYPE[y - i];      \
+  }
+
+#define DO_TEST(TYPE)                                          \
+  for (int i = 0; i < DIST * 2; ++i)                           \
+    {                                                          \
+      for (int j = 0; j < N + DIST * 2; ++j)                   \
+       a_##TYPE[j] = TEST_VALUE (j);                           \
+      test_##TYPE (i + N - 1, DIST + N - 1);                   \
+      for (int j = 0; j < N + DIST * 2; ++j)                   \
+       {                                                       \
+         TYPE expected;                                        \
+         if (j < i || j >= i + N)                              \
+           expected = TEST_VALUE (j);                          \
+         else if (i >= DIST)                                   \
+           expected = ((TYPE) TEST_VALUE (j)                   \
+                       + (TYPE) TEST_VALUE (j + DIST - i));    \
+         else                                                  \
+           expected = ((TYPE) TEST_VALUE (j)                   \
+                       + a_##TYPE[j + DIST - i]);              \
+         if (expected != a_##TYPE[j])                          \
+           __builtin_abort ();                                 \
+       }                                                       \
+    }
+
+FOR_EACH_TYPE (ADD_TEST)
+
+int
+main (void)
+{
+  FOR_EACH_TYPE (DO_TEST)
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump {flags: *WAR\n} "vect" { target vect_int } } } */
+/* { dg-final { scan-tree-dump "using an index-based overlap test" "vect" } } */
+/* { dg-final { scan-tree-dump-not "using an address-based" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-alias-check-19.c b/gcc/testsuite/gcc.dg/vect/vect-alias-check-19.c
new file mode 100644 (file)
index 0000000..583e296
--- /dev/null
@@ -0,0 +1,62 @@
+#define N 200
+#define DIST 32
+
+typedef signed char sc;
+typedef unsigned char uc;
+typedef signed short ss;
+typedef unsigned short us;
+typedef int si;
+typedef unsigned int ui;
+typedef signed long long sll;
+typedef unsigned long long ull;
+
+#define FOR_EACH_TYPE(M) \
+  M (sc) M (uc) \
+  M (ss) M (us) \
+  M (si) M (ui) \
+  M (sll) M (ull) \
+  M (float) M (double)
+
+#define ADD_TEST(TYPE)                         \
+  TYPE a_##TYPE[N * 2];                                \
+  void __attribute__((noinline, noclone))      \
+  test_##TYPE (int x, int y)                   \
+  {                                            \
+    for (int i = 0; i < N; ++i)                        \
+      {                                                \
+       a_##TYPE[i + x] = i;                    \
+       a_##TYPE[i + y] = 42 - i * 2;           \
+      }                                                \
+  }
+
+#define DO_TEST(TYPE)                                          \
+  for (int i = 0; i < DIST * 2; ++i)                           \
+    {                                                          \
+      __builtin_memset (a_##TYPE, 0, sizeof (a_##TYPE));       \
+      test_##TYPE (DIST, i);                                   \
+      for (int j = 0; j < N + DIST * 2; ++j)                   \
+       {                                                       \
+         TYPE expected = 0;                                    \
+         if (i > DIST && j >= i && j < i + N)                  \
+           expected = 42 - (j - i) * 2;                        \
+         if (j >= DIST && j < DIST + N)                        \
+           expected = j - DIST;                                \
+         if (i <= DIST && j >= i && j < i + N)                 \
+           expected = 42 - (j - i) * 2;                        \
+         if (expected != a_##TYPE[j])                          \
+           __builtin_abort ();                                 \
+       }                                                       \
+    }
+
+FOR_EACH_TYPE (ADD_TEST)
+
+int
+main (void)
+{
+  FOR_EACH_TYPE (DO_TEST)
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump {flags: *WAW\n} "vect" { target vect_int } } } */
+/* { dg-final { scan-tree-dump "using an index-based overlap test" "vect" } } */
+/* { dg-final { scan-tree-dump-not "using an address-based" "vect" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/vect-alias-check-20.c b/gcc/testsuite/gcc.dg/vect/vect-alias-check-20.c
new file mode 100644 (file)
index 0000000..8a699eb
--- /dev/null
@@ -0,0 +1,66 @@
+#define N 200
+#define DIST 32
+
+typedef signed char sc;
+typedef unsigned char uc;
+typedef signed short ss;
+typedef unsigned short us;
+typedef int si;
+typedef unsigned int ui;
+typedef signed long long sll;
+typedef unsigned long long ull;
+
+#define FOR_EACH_TYPE(M) \
+  M (sc) M (uc) \
+  M (ss) M (us) \
+  M (si) M (ui) \
+  M (sll) M (ull) \
+  M (float) M (double)
+
+#define TEST_VALUE(I) ((I) * 11 / 2)
+
+#define ADD_TEST(TYPE)                         \
+  TYPE a_##TYPE[N * 2];                                \
+  TYPE __attribute__((noinline, noclone))      \
+  test_##TYPE (int x, int y)                   \
+  {                                            \
+    TYPE res = 0;                              \
+    for (int i = 0; i < N; ++i)                        \
+      {                                                \
+       a_##TYPE[i + x] = i;                    \
+       res += a_##TYPE[i + y];                 \
+      }                                                \
+    return res;                                        \
+  }
+
+#define DO_TEST(TYPE)                                          \
+  for (int i = 0; i < DIST * 2; ++i)                           \
+    {                                                          \
+      for (int j = 0; j < N + DIST * 2; ++j)                   \
+       a_##TYPE[j] = TEST_VALUE (j);                           \
+      TYPE res = test_##TYPE (DIST, i);                                \
+      for (int j = 0; j < N; ++j)                              \
+       if (a_##TYPE[j + DIST] != (TYPE) j)                     \
+         __builtin_abort ();                                   \
+      TYPE expected_res = 0;                                   \
+      for (int j = i; j < i + N; ++j)                          \
+       if (i <= DIST && j >= DIST && j < DIST + N)             \
+         expected_res += j - DIST;                             \
+       else                                                    \
+         expected_res += TEST_VALUE (j);                       \
+      if (expected_res != res)                                 \
+       __builtin_abort ();                                     \
+    }
+
+FOR_EACH_TYPE (ADD_TEST)
+
+int
+main (void)
+{
+  FOR_EACH_TYPE (DO_TEST)
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump {flags: *RAW\n} "vect" { target vect_int } } } */
+/* { dg-final { scan-tree-dump "using an index-based overlap test" "vect" } } */
+/* { dg-final { scan-tree-dump-not "using an address-based" "vect" } } */
index 527cb5eca9c76efe358b3b19ff865f9a228d427b..4dfa33404e3da0b15f395678987fa326d08e6ea9 100644 (file)
@@ -1743,7 +1743,9 @@ prune_runtime_alias_test_list (vec<dr_with_seg_len_pair_t> *alias_pairs,
 
    We can create expression based on index rather than address:
 
-     (i_0 + 4 < j_0 || j_0 + 4 < i_0)
+     (unsigned) (i_0 - j_0 + 3) <= 6
+
+   i.e. the indices are less than 4 apart.
 
    Note evolution step of index needs to be considered in comparison.  */
 
@@ -1780,15 +1782,8 @@ create_intersect_range_checks_index (class loop *loop, tree *cond_expr,
   if (neg_step)
     {
       abs_step = -abs_step;
-      seg_len1 = -seg_len1;
-      seg_len2 = -seg_len2;
-    }
-  else
-    {
-      /* Include the access size in the length, so that we only have one
-        tree addition below.  */
-      seg_len1 += dr_a.access_size;
-      seg_len2 += dr_b.access_size;
+      seg_len1 = (-wi::to_poly_wide (dr_a.seg_len)).force_uhwi ();
+      seg_len2 = (-wi::to_poly_wide (dr_b.seg_len)).force_uhwi ();
     }
 
   /* Infer the number of iterations with which the memory segment is accessed
@@ -1802,16 +1797,13 @@ create_intersect_range_checks_index (class loop *loop, tree *cond_expr,
       || !can_div_trunc_p (seg_len2 + abs_step - 1, abs_step, &niter_len2))
     return false;
 
-  poly_uint64 niter_access1 = 0, niter_access2 = 0;
-  if (neg_step)
-    {
-      /* Divide each access size by the byte step, rounding up.  */
-      if (!can_div_trunc_p (dr_a.access_size - abs_step - 1,
-                           abs_step, &niter_access1)
-         || !can_div_trunc_p (dr_b.access_size + abs_step - 1,
-                              abs_step, &niter_access2))
-       return false;
-    }
+  /* Divide each access size by the byte step, rounding up.  */
+  poly_uint64 niter_access1, niter_access2;
+  if (!can_div_trunc_p (dr_a.access_size + abs_step - 1,
+                       abs_step, &niter_access1)
+      || !can_div_trunc_p (dr_b.access_size + abs_step - 1,
+                          abs_step, &niter_access2))
+    return false;
 
   unsigned int i;
   for (i = 0; i < DR_NUM_DIMENSIONS (dr_a.dr); i++)
@@ -1851,38 +1843,87 @@ create_intersect_range_checks_index (class loop *loop, tree *cond_expr,
         index of data reference.  Like segment length, index length is
         linear function of the number of iterations with index_step as
         the coefficient, i.e, niter_len * idx_step.  */
-      tree idx_len1 = fold_build2 (MULT_EXPR, TREE_TYPE (min1), idx_step,
-                                  build_int_cst (TREE_TYPE (min1),
-                                                 niter_len1));
-      tree idx_len2 = fold_build2 (MULT_EXPR, TREE_TYPE (min2), idx_step,
-                                  build_int_cst (TREE_TYPE (min2),
-                                                 niter_len2));
-      tree max1 = fold_build2 (PLUS_EXPR, TREE_TYPE (min1), min1, idx_len1);
-      tree max2 = fold_build2 (PLUS_EXPR, TREE_TYPE (min2), min2, idx_len2);
-      /* Adjust ranges for negative step.  */
+      offset_int abs_idx_step = offset_int::from (wi::to_wide (idx_step),
+                                                 SIGNED);
       if (neg_step)
-       {
-         /* IDX_LEN1 and IDX_LEN2 are negative in this case.  */
-         std::swap (min1, max1);
-         std::swap (min2, max2);
-
-         /* As with the lengths just calculated, we've measured the access
-            sizes in iterations, so multiply them by the index step.  */
-         tree idx_access1
-           = fold_build2 (MULT_EXPR, TREE_TYPE (min1), idx_step,
-                          build_int_cst (TREE_TYPE (min1), niter_access1));
-         tree idx_access2
-           = fold_build2 (MULT_EXPR, TREE_TYPE (min2), idx_step,
-                          build_int_cst (TREE_TYPE (min2), niter_access2));
-
-         /* MINUS_EXPR because the above values are negative.  */
-         max1 = fold_build2 (MINUS_EXPR, TREE_TYPE (max1), max1, idx_access1);
-         max2 = fold_build2 (MINUS_EXPR, TREE_TYPE (max2), max2, idx_access2);
-       }
-      tree part_cond_expr
-       = fold_build2 (TRUTH_OR_EXPR, boolean_type_node,
-           fold_build2 (LE_EXPR, boolean_type_node, max1, min2),
-           fold_build2 (LE_EXPR, boolean_type_node, max2, min1));
+       abs_idx_step = -abs_idx_step;
+      poly_offset_int idx_len1 = abs_idx_step * niter_len1;
+      poly_offset_int idx_len2 = abs_idx_step * niter_len2;
+      poly_offset_int idx_access1 = abs_idx_step * niter_access1;
+      poly_offset_int idx_access2 = abs_idx_step * niter_access2;
+
+      gcc_assert (known_ge (idx_len1, 0)
+                 && known_ge (idx_len2, 0)
+                 && known_ge (idx_access1, 0)
+                 && known_ge (idx_access2, 0));
+
+      /* Each access has the following pattern, with lengths measured
+        in units of INDEX:
+
+             <-- idx_len -->
+             <--- A: -ve step --->
+             +-----+-------+-----+-------+-----+
+             | n-1 | ..... |  0  | ..... | n-1 |
+             +-----+-------+-----+-------+-----+
+                           <--- B: +ve step --->
+                           <-- idx_len -->
+                           |
+                          min
+
+        where "n" is the number of scalar iterations covered by the segment
+        and where each access spans idx_access units.
+
+        A is the range of bytes accessed when the step is negative,
+        B is the range when the step is positive.
+
+        When checking for general overlap, we need to test whether
+        the range:
+
+          [min1 + low_offset1, min2 + high_offset1 + idx_access1 - 1]
+
+        overlaps:
+
+          [min2 + low_offset2, min2 + high_offset2 + idx_access2 - 1]
+
+        where:
+
+           low_offsetN = +ve step ? 0 : -idx_lenN;
+          high_offsetN = +ve step ? idx_lenN : 0;
+
+        This is equivalent to testing whether:
+
+          min1 + low_offset1 <= min2 + high_offset2 + idx_access2 - 1
+          && min2 + low_offset2 <= min1 + high_offset1 + idx_access1 - 1
+
+        Converting this into a single test, there is an overlap if:
+
+          0 <= min2 - min1 + bias <= limit
+
+        where  bias = high_offset2 + idx_access2 - 1 - low_offset1
+              limit = (high_offset1 - low_offset1 + idx_access1 - 1)
+                    + (high_offset2 - low_offset2 + idx_access2 - 1)
+         i.e. limit = idx_len1 + idx_access1 - 1 + idx_len2 + idx_access2 - 1
+
+        Combining the tests requires limit to be computable in an unsigned
+        form of the index type; if it isn't, we fall back to the usual
+        pointer-based checks.  */
+      poly_offset_int limit = (idx_len1 + idx_access1 - 1
+                              + idx_len2 + idx_access2 - 1);
+      tree utype = unsigned_type_for (TREE_TYPE (min1));
+      if (!wi::fits_to_tree_p (limit, utype))
+       return false;
+
+      poly_offset_int low_offset1 = neg_step ? -idx_len1 : 0;
+      poly_offset_int high_offset2 = neg_step ? 0 : idx_len2;
+      poly_offset_int bias = high_offset2 + idx_access2 - 1 - low_offset1;
+
+      tree subject = fold_build2 (MINUS_EXPR, utype,
+                                 fold_convert (utype, min2),
+                                 fold_convert (utype, min1));
+      subject = fold_build2 (PLUS_EXPR, utype, subject,
+                            wide_int_to_tree (utype, bias));
+      tree part_cond_expr = fold_build2 (GT_EXPR, boolean_type_node, subject,
+                                        wide_int_to_tree (utype, limit));
       if (*cond_expr)
        *cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
                                  *cond_expr, part_cond_expr);