vect: Fix wrong code with pr108692.c on targets with only non-widening ABD [PR118727]

With things like

  // signed char a_14, a_16;
  a.0_4 = (unsigned char) a_14;
  _5 = (int) a.0_4;
  b.1_6 = (unsigned char) b_16;
  _7 = (int) b.1_6;
  c_17 = _5 - _7;
  _8 = ABS_EXPR <c_17>;
  r_18 = _8 + r_23;

An ABD pattern will be recognized for _8:

  patt_31 = .ABD (a.0_4, b.1_6);

It's still correct.  But then when the SAD pattern is recognized:

  patt_29 = SAD_EXPR <a_14, b_16, r_23>;

This is not correct.  This only happens for targets with both uabd and
sabd but not vec_widen_{s,u}abd, currently LoongArch is the only target
affected.

The problem is vect_look_through_possible_promotion will throw away a
series of conversions if the effect is equivalent to a sign change and a
promotion, but here the sign change is definitely relevant, and the
promotion is also relevant for "mixed sign" cases like
r += abs((unsigned int)(unsigned char) a - (signed int)(signed char) b
(we need to promote to HImode as the difference can exceed the range of
QImode).

If there were any redundant promotion, it should have been stripped in
vect_recog_abd_pattern (i.e. when patt_31 = .ABD (a.0_4, b.1_6) is
recognized) instead of in vect_recog_sad_pattern, or we'd have a
missed-optimization if the ABD output is not summerized.  So anyway
vect_recog_sad_pattern is just not a proper location to call
vect_look_through_possible_promotion for the ABD inputs, remove the
calls to fix the issue.

gcc/ChangeLog:

	PR tree-optimization/118727
	* tree-vect-patterns.cc (vect_recog_sad_pattern): Don't call
	vect_look_through_possible_promotion on ABD inputs.

gcc/testsuite/ChangeLog:

	PR tree-optimization/118727
	* gcc.dg/pr108692.c: Mention PR 118727 in the comment.
	* gcc.dg/pr118727.c: New test case.

diff --git a/gcc/testsuite/gcc.dg/pr108692.c b/gcc/testsuite/gcc.dg/pr108692.c
index 13a27496ad9f90dbd0bd5cb043856bbad3b5a4c1..eeee220328172fa68f4ecb6981adec0f9fa8c5db 100644 (file)
--- a/gcc/testsuite/gcc.dg/pr108692.c
+++ b/gcc/testsuite/gcc.dg/pr108692.c
@@ -1,4 +1,5 @@
 /* PR tree-optimization/108692 */
+/* PR tree-optimization/118727 */
 /* { dg-do run } */
 /* { dg-options "-O2 -ftree-vectorize" } */
 

diff --git a/gcc/testsuite/gcc.dg/pr118727.c b/gcc/testsuite/gcc.dg/pr118727.c
new file mode 100644 (file)
index 0000000..2ee5fa7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr118727.c
@@ -0,0 +1,32 @@
+/* PR tree-optimization/118727 */
+/* { dg-do run } */
+/* { dg-options "-O2 -ftree-vectorize" } */
+
+__attribute__((noipa)) int
+foo (signed char *x, signed char *y, int n)
+{
+  int i, r = 0;
+  signed char a, b;
+  for (i = 0; i < n; i++)
+    {
+      a = x[i];
+      b = y[i];
+      /* Slightly twisted from pr108692.c.  */
+      int c = (unsigned int)(unsigned char) a - (signed int)(signed char) b;
+      r = r + (c < 0 ? -c : c);
+    }
+  return r;
+}
+
+int
+main ()
+{
+  signed char x[64] = {}, y[64] = {};
+  if (__CHAR_BIT__ != 8 || __SIZEOF_INT__ != 4)
+    return 0;
+  x[32] = -1;
+  y[32] = -128;
+  if (foo (x, y, 64) != 383)
+    __builtin_abort ();
+  return 0;
+}

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 5aebf9505485b6b7f7abded876822f2518ef9503..6fc97d1b6ef91ee4293aee6d64beb317f5094d3f 100644 (file)
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -1405,15 +1405,8 @@ vect_recog_sad_pattern (vec_info *vinfo,
       tree abd_oprnd0 = gimple_call_arg (abd_stmt, 0);
       tree abd_oprnd1 = gimple_call_arg (abd_stmt, 1);
 
-      if (gimple_call_internal_fn (abd_stmt) == IFN_ABD)
-       {
-         if (!vect_look_through_possible_promotion (vinfo, abd_oprnd0,
-                                                    &unprom[0])
-             || !vect_look_through_possible_promotion (vinfo, abd_oprnd1,
-                                                       &unprom[1]))
-           return NULL;
-       }
-      else if (gimple_call_internal_fn (abd_stmt) == IFN_VEC_WIDEN_ABD)
+      if (gimple_call_internal_fn (abd_stmt) == IFN_ABD
+         || gimple_call_internal_fn (abd_stmt) == IFN_VEC_WIDEN_ABD)
        {
          unprom[0].op = abd_oprnd0;
          unprom[0].type = TREE_TYPE (abd_oprnd0);