From c91db798ec65b3e55f2380ca1530ecb71544f1bb Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Wed, 27 Jan 2021 15:20:58 +0100
Subject: [PATCH] tree-optimization/98854 - avoid some PHI BB vectorization
This avoids cases of PHI node vectorization that just causes us
to insert vector CTORs inside loops for values only required
outside of the loop.
2021-01-27 Richard Biener <rguenther@suse.de>
PR tree-optimization/98854
* tree-vect-slp.c (vect_build_slp_tree_2): Also build
PHIs from scalars when the number of CTORs matches the
number of children.
* gcc.dg/vect/bb-slp-pr98854.c: New testcase.
---
gcc/testsuite/gcc.dg/vect/bb-slp-pr98854.c | 24 ++++++++++++++++++++++
gcc/tree-vect-slp.c | 5 ++++-
2 files changed, 28 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-pr98854.c
diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr98854.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr98854.c
new file mode 100644
index 000000000000..0c8141e1d17a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr98854.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+
+double a[1024];
+
+int bar();
+void foo (int n)
+{
+ double x = 0, y = 0;
+ int i = 1023;
+ do
+ {
+ x += a[i] + a[i+1];
+ y += a[i] / a[i+1];
+ if (bar ())
+ break;
+ }
+ while (--i);
+ /* We want to avoid vectorizing the LC PHI and insert vector CTORs
+ inside of the loop where it is only needed here. */
+ a[0] = x;
+ a[1] = y;
+}
+
+/* { dg-final { scan-tree-dump-not "vectorizing SLP node starting from: ._\[0-9\]+ = PHI" "slp1" } } */
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 4465cf7494ee..10b876ff5ede 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -1896,7 +1896,10 @@ fail:
n_vector_builds++;
}
}
- if (all_uniform_p || n_vector_builds > 1)
+ if (all_uniform_p
+ || n_vector_builds > 1
+ || (n_vector_builds == children.length ()
+ && is_a <gphi *> (stmt_info->stmt)))
{
/* Roll back. */
matches[0] = false;
--
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