[PATCH PR85804]Fix wrong code by correcting bump step computation in vector(1) load of single-element group access

[Bin Cheng]

Hi,
As reported in PR85804, bump step is wrongly computed for vector(1) load of
single-element group access.  This patch fixes the issue by correcting bump
step computation for the specific VMAT_CONTIGUOUS case.

Bootstrap and test on x86_64 and AArch64 ongoing, is it OK?

Thanks,
bin

2018-05-17  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/85804
        * tree-vect-stmts.c (vectorizable_load): Compute correct bump step
        for vector(1) load in single-element group access.

gcc/testsuite
2018-05-17  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/85804
        * gcc.c-torture/execute/pr85804.c: New test.
From 502bcd1e445186a56b6ea254a0cd2406fb62f08c Mon Sep 17 00:00:00 2001
From: Bin Cheng <binch...@e108451-lin.cambridge.arm.com>
Date: Fri, 18 May 2018 14:18:14 +0100
Subject: [PATCH] pr85804-20180517

---
 gcc/testsuite/gcc.c-torture/execute/pr85804.c | 22 ++++++++++++++++++++++
 gcc/tree-vect-stmts.c                         | 15 +++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr85804.c

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr85804.c b/gcc/testsuite/gcc.c-torture/execute/pr85804.c
new file mode 100644
index 0000000..b8929b1
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr85804.c
@@ -0,0 +1,22 @@
+/* { dg-options "-O2 -ftree-vectorize -fno-vect-cost-model" } */
+
+long d[64] = {0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+              0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+              0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+              0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+void abort ();
+void __attribute__((noinline)) foo (int b)
+{
+  if (b)
+    abort ();
+}
+int main() {
+  int b = 0;
+  for (int c = 0; c <= 5; c++)
+    b ^= d[c * 5 + 1];
+  foo (b);
+  return 0;
+}
+
diff --git a/gcc/tree-vect-stmts.c b/gcc/tree-vect-stmts.c
index 64a157d..e6b95b3 100644
--- a/gcc/tree-vect-stmts.c
+++ b/gcc/tree-vect-stmts.c
@@ -7262,6 +7262,7 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
   gphi *phi = NULL;
   vec<tree> dr_chain = vNULL;
   bool grouped_load = false;
+  bool single_element = false;
   gimple *first_stmt;
   gimple *first_stmt_for_drptr = NULL;
   bool inv_p;
@@ -7822,6 +7823,15 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
       first_stmt = stmt;
       first_dr = dr;
       group_size = vec_num = 1;
+      /* For single-element vector in a single-element group, record the group
+	 size in order to compute correct bump size.  */
+      if (!slp
+	  && memory_access_type == VMAT_CONTIGUOUS
+	  && STMT_VINFO_GROUPED_ACCESS (stmt_info))
+	{
+	  single_element = true;
+	  group_size = GROUP_SIZE (vinfo_for_stmt (first_stmt));
+	}
       group_gap_adj = 0;
       ref_type = reference_alias_ptr_type (DR_REF (first_dr));
     }
@@ -7992,6 +8002,11 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
       else
 	aggr_type = vectype;
       bump = vect_get_data_ptr_increment (dr, aggr_type, memory_access_type);
+      /* Multiply bump size by group size for single-element vector in single-
+	 element group.  */
+      if (single_element && group_size > 1)
+	bump = fold_build2 (MULT_EXPR, TREE_TYPE (bump), bump,
+			    build_int_cst (TREE_TYPE (bump), group_size));
     }
 
   tree vec_mask = NULL_TREE;
-- 
1.9.1