From 6de2e0d400cbe46da482a672810c37b1832c408c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=83=91=E6=99=A8=E5=8D=89?= <zhengchenhui1@huawei.com>
Date: Thu, 25 Jul 2024 19:45:43 +0800
Subject: [PATCH] Improve non-loop disambiguation

This optimization is brought from https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=038b077689bb5310386b04d40a2cea234f01e6aa.

When dr_may_alias_p is called without a loop context, it tries
to use the tree-affine interface to calculate the difference
between the two addresses and use that difference to check whether
the gap between the accesses is known at compile time.  However, as the
example in the PR shows, this doesn't expand SSA_NAMEs and so can easily
be defeated by things like reassociation.

One fix would have been to use aff_combination_expand to expand the
SSA_NAMEs, but we'd then need some way of maintaining the associated
cache.  This patch instead reuses the innermost_loop_behavior fields
(which exist even when no loop context is provided).

It might still be useful to do the aff_combination_expand thing too,
if an example turns out to need it.
---
 gcc/common.opt                              |  4 ++++
 gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c | 16 +++++++++++++++
 gcc/tree-data-ref.cc                        | 22 +++++++++++++++++++++
 3 files changed, 42 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c

diff --git a/gcc/common.opt b/gcc/common.opt
index b18f0b944..75bf9c9c1 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -3217,6 +3217,10 @@ ftree-loop-vectorize
 Common Var(flag_tree_loop_vectorize) Optimization EnabledBy(ftree-vectorize)
 Enable loop vectorization on trees.
 
+falias-analysis-expand-ssa
+Common Var(flag_alias_analysis_expand_ssa) Init(0)
+Enable expanded SSA name analysis during alias analysis.
+
 ftree-slp-vectorize
 Common Var(flag_tree_slp_vectorize) Optimization EnabledBy(ftree-vectorize)
 Enable basic block vectorization (SLP) on trees.
diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
new file mode 100644
index 000000000..5ff8a8a62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-falias-analysis-expand-ssa" } */
+
+void f(double *p, long i)
+{
+    p[i+0] += 1;
+    p[i+1] += 1;
+}
+void g(double *p, long i)
+{
+    double *q = p + i;
+    q[0] += 1;
+    q[1] += 1;
+}
+
+/* { dg-final { scan-tree-dump-not "can't determine dependence" slp2 } } */
diff --git a/gcc/tree-data-ref.cc b/gcc/tree-data-ref.cc
index e6ae9e847..a05073c51 100644
--- a/gcc/tree-data-ref.cc
+++ b/gcc/tree-data-ref.cc
@@ -2993,6 +2993,28 @@ dr_may_alias_p (const struct data_reference *a, const struct data_reference *b,
      disambiguation.  */
   if (!loop_nest)
     {
+      if (flag_alias_analysis_expand_ssa)
+	{
+	  tree tree_size_a = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (a)));
+	  tree tree_size_b = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (b)));
+
+	  if (DR_BASE_ADDRESS (a)
+	     && DR_BASE_ADDRESS (b)
+	     && operand_equal_p (DR_BASE_ADDRESS (a), DR_BASE_ADDRESS (b))
+	     && operand_equal_p (DR_OFFSET (a), DR_OFFSET (b))
+	     && poly_int_tree_p (tree_size_a)
+	     && poly_int_tree_p (tree_size_b)
+	     && !ranges_maybe_overlap_p (wi::to_widest (DR_INIT (a)),
+					 wi::to_widest (tree_size_a),
+					 wi::to_widest (DR_INIT (b)),
+					 wi::to_widest (tree_size_b)))
+	     {
+	       gcc_assert (integer_zerop (DR_STEP (a))
+	     		   && integer_zerop (DR_STEP (b)));
+	       return false;
+	     }
+	}
+
       aff_tree off1, off2;
       poly_widest_int size1, size2;
       get_inner_reference_aff (DR_REF (a), &off1, &size1);
-- 
2.33.0