arc: Fix for loop end detection

We use a negative ID number to link together the doloop_begin and
doloop_end instructions.  This negative ID number is setup within
doloop_begin, at this point the ID is stored into the loop end
instruction (doloop_end_i) and placed into the doloop_begin_i
instruction.

In arc.c (arc_reorg) we extract the ID from the doloop_end_i
instruction in order to find the matching doloop_begin_i instruction,
though the ID is only used in some cases.

Currently in arc_reorg when we extract the ID we negate it.  This
negation is invalid.  The ID stored in both doloop_end_i and
doloop_begin_i is already negative, the negation in arc_reorg means
that if we need to use the ID to find the doloop_begin_i then we will
never find it (as the IDs will never match).

This commit removes the unneeded negation, moves the extraction of the
ID into a more appropriately scoped block and adds a new test for this
issue.

gcc/ChangeLog:

	* config/arc/arc.c (arc_reorg): Move loop_end_id into a more local
	block, and do not negate it, the stored id is already negative.

gcc/testsuite/ChangeLog:

	* gcc.target/arc/loop-1.c: New file.


Co-Authored-By: Guy Benyei <guybe@mellanox.com>

From-SVN: r246933

4 files changed, 58 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8c4728c..2807eb2 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,4 +1,10 @@
 2017-04-14  Andrew Burgess  <andrew.burgess@embecosm.com>
+	    Guy Benyei  <guybe@mellanox.com>
+
+	* config/arc/arc.c (arc_reorg): Move loop_end_id into a more local
+	block, and do not negate it, the stored id is already negative.
+
+2017-04-14  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* config/arc/arc.md (doloop_begin_i): Use @pcl assembler syntax.
 
diff --git a/gcc/config/arc/arc.c b/gcc/config/arc/arc.c
index c8ffa1a..92fecad 100644
--- a/gcc/config/arc/arc.c
+++ b/gcc/config/arc/arc.c
@@ -6569,8 +6569,6 @@ arc_reorg (void)
 	  rtx_insn *lp_simple = NULL;
 	  rtx_insn *next = NULL;
 	  rtx op0 = XEXP (XVECEXP (PATTERN (insn), 0, 1), 0);
-	  HOST_WIDE_INT loop_end_id
-	    = -INTVAL (XEXP (XVECEXP (PATTERN (insn), 0, 4), 0));
 	  int seen_label = 0;
 
 	  for (lp = prev;
@@ -6581,6 +6579,9 @@ arc_reorg (void)
 	  if (!lp || !NONJUMP_INSN_P (lp)
 	      || dead_or_set_regno_p (lp, LP_COUNT))
 	    {
+	      HOST_WIDE_INT loop_end_id
+		= INTVAL (XEXP (XVECEXP (PATTERN (insn), 0, 4), 0));
+
 	      for (prev = next = insn, lp = NULL ; prev || next;)
 		{
 		  if (prev)
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index a1d74b6..3de763f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2017-04-14  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gcc.target/arc/loop-1.c: New file.
+
 2017-04-14  Michael Meissner  <meissner@linux.vnet.ibm.com>
 
 	PR target/80098
diff --git a/gcc/testsuite/gcc.target/arc/loop-1.c b/gcc/testsuite/gcc.target/arc/loop-1.c
new file mode 100644
index 0000000..1afe8eb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arc/loop-1.c
@@ -0,0 +1,45 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+/* This case would fail to make use of the zero-overhead loop
+   instruction at one time due to a bug.  */
+
+extern char a[];
+
+struct some_t
+{
+  struct
+  {
+    int aaa;
+    short bbb;
+    char ccc;
+    char ddd;
+  } ppp[8];
+
+  int www[1];
+};
+
+int b;
+
+void
+some_function ()
+{
+  struct some_t *tmp = (struct some_t *) a;
+
+  while ((*tmp).ppp[b].ccc)
+    while(0);
+
+  for (; b; b++)
+    {
+      if (tmp->ppp[b].ccc)
+        {
+          int c = tmp->ppp[b].bbb;
+          int d = tmp->ppp[b].aaa;
+          int e = d - tmp->www[c];
+          if (e)
+            tmp->ppp[b].ddd = 1;
+        }
+    }
+}
+
+/* { dg-final { scan-assembler "\[^\n\]+lp \\.L__GCC__" } } */