From: Richard Sandiford <richard.sandiford@arm.com>
Date: Tue, 20 Sep 2022 14:27:46 +0000 (+0100)
Subject: vect: Fix missed gather load opportunity
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=833d374cd75810b8831f84c00c60c23d9e77788f;p=thirdparty%2Fgcc.git

vect: Fix missed gather load opportunity

While writing a testcase for PR106794, I noticed that we failed
to vectorise the testcase in the patch for SVE.  The code that
recognises gather loads tries to optimise the point at which
the offset is calculated, to avoid unnecessary extensions or
truncations:

	  /* Don't include the conversion if the target is happy with
	     the current offset type.  */

But breaking only makes sense if we're at an SSA_NAME (which could
then be vectorised).  We shouldn't break on a conversion embedded
in a generic expression.

gcc/
	* tree-vect-data-refs.cc (vect_check_gather_scatter): Restrict
	early-out optimisation to SSA_NAMEs.

gcc/testsuite/
	* gcc.dg/vect/vect-gather-5.c: New test.

(cherry picked from commit 4a773bf2f08656a39ac75cf6b4871c8cec8b5007)
---

diff --git a/gcc/ChangeLog.omp b/gcc/ChangeLog.omp
index 3a3e54bdeb23..fdccdabf72b1 100644
--- a/gcc/ChangeLog.omp
+++ b/gcc/ChangeLog.omp
@@ -1,3 +1,10 @@
+2023-03-17  Andrew Stubbs  <ams@codesourcery.com>
+
+	Backport from mainline:
+	Richard Sandiford <richard.sandiford@arm.com>
+	* tree-vect-data-refs.cc (vect_check_gather_scatter): Restrict
+	early-out optimisation to SSA_NAMEs.
+
 2023-03-17  Andrew Stubbs  <ams@codesourcery.com>
 
 	* config/gcn/gcn-valu.md (gather_load<mode><vndi>): New.
diff --git a/gcc/testsuite/ChangeLog.omp b/gcc/testsuite/ChangeLog.omp
index 860ecdc780b5..19357b0b5c27 100644
--- a/gcc/testsuite/ChangeLog.omp
+++ b/gcc/testsuite/ChangeLog.omp
@@ -1,3 +1,9 @@
+2023-03-17  Andrew Stubbs  <ams@codesourcery.com>
+
+	Backport from mainline:
+	Richard Sandiford <richard.sandiford@arm.com>
+	* gcc.dg/vect/vect-gather-5.c: New test.
+
 2023-03-06  Paul-Antoine Arras <pa@codesourcery.com>
 
 	Backported from master:
diff --git a/gcc/testsuite/gcc.dg/vect/vect-gather-5.c b/gcc/testsuite/gcc.dg/vect/vect-gather-5.c
new file mode 100644
index 000000000000..8b5074bba885
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-gather-5.c
@@ -0,0 +1,42 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O3" } */
+
+#ifdef __aarch64__
+#pragma GCC target "+sve"
+#endif
+
+long a[100], b[100], c[100];
+
+void g1 ()
+{
+  for (int i = 0; i < 100; i += 2)
+    {
+      c[i] += a[b[i]] + 1;
+      c[i + 1] += a[b[i + 1]] + 2;
+    }
+}
+
+long g2 ()
+{
+  long res = 0;
+  for (int i = 0; i < 100; i += 2)
+    {
+      res += a[b[i + 1]];
+      res += a[b[i]];
+    }
+  return res;
+}
+
+long g3 ()
+{
+  long res = 0;
+  for (int i = 0; i < 100; i += 2)
+    {
+      res += a[b[i]];
+      res += a[b[i + 1]];
+    }
+  return res;
+}
+
+/* { dg-final { scan-tree-dump-times {add new stmt[^\n]*GATHER_LOAD} 3 "vect" { target aarch64*-*-* } } } */
+/* { dg-final { scan-tree-dump-not {add new stmt[^\n]*VEC_PERM_EXPR} "vect" { target aarch64*-*-* } } } */
diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index 70b671ed94aa..21a7192bf24a 100644
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -4151,6 +4151,7 @@ vect_check_gather_scatter (stmt_vec_info stmt_info, loop_vec_info loop_vinfo,
 	  /* Don't include the conversion if the target is happy with
 	     the current offset type.  */
 	  if (use_ifn_p
+	      && TREE_CODE (off) == SSA_NAME
 	      && !POINTER_TYPE_P (TREE_TYPE (off))
 	      && vect_gather_scatter_fn_p (loop_vinfo, DR_IS_READ (dr),
 					   masked_p, vectype, memory_type,