https://gcc.gnu.org/g:da88e7027a34a44de84f6d8d5a96d262c29080a7
commit r15-7370-gda88e7027a34a44de84f6d8d5a96d262c29080a7
Author: Xi Ruoyao <xry...@xry111.site>
Date: Sun Feb 2 21:22:36 2025 +0800
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:
---
gcc/testsuite/gcc.dg/pr108692.c | 1 +
gcc/testsuite/gcc.dg/pr118727.c | 32 ++++++++++++++++++++++++++++++++
gcc/tree-vect-patterns.cc | 11 ++---------
3 files changed, 35 insertions(+), 9 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/pr108692.c b/gcc/testsuite/gcc.dg/pr108692.c
index 13a27496ad9f..eeee22032817 100644
--- 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
index 000000000000..2ee5fa782362
--- /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 5aebf9505485..6fc97d1b6ef9 100644
--- 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);
