[PATCH PR81267]Rewrite into loop closed ssa form in case of any store-store chain

[Bin Cheng]

Hi,
This simple patch fixes the ICE by rewriting into loop closed ssa form in case
of any store-store chain.  We maybe able to avoid that for some cases that
eliminated stores only store loop invariant values, but only with more checks
when inserting final store instructions.
Bootstrap and test on x86_64 and AArch64 ongoing.  Is it OK?

Thanks,
bin
2017-07-31  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/81627
        * tree-predcom.c (prepare_finalizers): Always rewrite into loop
        closed ssa form for store-store chain.

gcc/testsuite/ChangeLog
2017-07-31  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/81627
        * gcc.dg/tree-ssa/pr81627.c: New.
From d366015187de926a8fe3248325b229bed99b27b5 Mon Sep 17 00:00:00 2001
From: Bin Cheng <binch...@e108451-lin.cambridge.arm.com>
Date: Mon, 31 Jul 2017 11:16:44 +0100
Subject: [PATCH 2/2] pr81627-20170731.txt

---
 gcc/testsuite/gcc.dg/tree-ssa/pr81627.c | 28 ++++++++++++++++++++++++++++
 gcc/tree-predcom.c                      | 10 +++++-----
 2 files changed, 33 insertions(+), 5 deletions(-)
 create mode 100755 gcc/testsuite/gcc.dg/tree-ssa/pr81627.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr81627.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr81627.c
new file mode 100755
index 0000000..7421c49
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr81627.c
@@ -0,0 +1,28 @@
+/* { dg-do run } */
+/* { dg-options "-O3 -fno-tree-loop-vectorize -fdump-tree-pcom-details" } */
+
+int a, b, c, d[6], e = 3, f;
+
+void abort (void);
+void fn1 ()
+{
+  for (b = 1; b < 5; b++)
+    {
+      for (c = 0; c < 5; c++)
+        d[b] = e;
+      if (a)
+        f++;
+      d[b + 1] = 1;
+    }
+}
+
+int main ()
+{
+  fn1 ();
+  if (d[0] != 0 || d[1] != 3 || d[2] != 3
+      || d[3] != 3 || d[4] != 3 || d[5] != 1)
+    abort ();
+
+  return 0;
+}
+/* { dg-final { scan-tree-dump-times "Store-stores chain" 1 "pcom" } } */
diff --git a/gcc/tree-predcom.c b/gcc/tree-predcom.c
index f7a57a4..4538773 100644
--- a/gcc/tree-predcom.c
+++ b/gcc/tree-predcom.c
@@ -2983,11 +2983,11 @@ prepare_finalizers (struct loop *loop, vec<chain_p> 
chains)
       if (prepare_finalizers_chain (loop, chain))
        {
          i++;
-         /* We don't corrupt loop closed ssa form for store elimination
-            chain if eliminated stores only store loop invariant values
-            into memory.  */
-         if (!chain->inv_store_elimination)
-           loop_closed_ssa |= (!chain->inv_store_elimination);
+         /* Be conservative, assume loop closed ssa form is corrupted
+            by store-store chain.  Though it's not always the case if
+            eliminated stores only store loop invariant values into
+            memory.  */
+         loop_closed_ssa = true;
        }
       else
        {
-- 
1.9.1