[PATCH PR81832]Skip copying loop header if inner loop is distributed

[Bin Cheng <Bin.Cheng@arm.com>]

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Hi,
This patch fixes PR81832.  Root cause for the ICE is:
  1) Loop has distributed inner loop.
  2) The guarding function call IFN_LOOP_DIST_CALL happens to be in loop's header.
  3) IFN_LOOP_DIST_CALL (int loop's header) is duplicated by pass_ch_vect thus
     not eliminated.

Given pass_ch_vect copies loop header to enable more vectorization, we should
skip loop in this case because distributed inner loop means this loop can not
be vectorized anyway.  One point to mention is name inner_loop_distributed_p
is a little misleading.  The name indicates that each basic block is checked,
but the patch only checks loop's header for simplicity/efficiency's purpose.
Any comment?
Bootstrap and test on x86_64.

Thanks,
bin
2017-08-15  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/81832
	* tree-ssa-loop-ch.c (inner_loop_distributed_p): New function.
	(pass_ch_vect::process_loop_p): Call above function.

gcc/testsuite
2017-08-15  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/81832
	* gcc.dg/tree-ssa/pr81832.c: New test.

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diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr81832.c b/gcc/testsuite/gcc.dg/tree-ssa/pr81832.c
new file mode 100644
index 0000000..893124e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr81832.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+int a, b, *c;
+void d(void)
+{
+    int **e;
+    for(;;)
+        for(int f = 1; f <= 6; f++)
+        {
+            b = 0;
+            if(a)
+g:
+                while(a++);
+            if (**e);
+            else
+            {
+                *c = a;
+                goto g;
+            }
+        }
+}
diff --git a/gcc/tree-ssa-loop-ch.c b/gcc/tree-ssa-loop-ch.c
index 14cc6d8d..3c217d4 100644
--- a/gcc/tree-ssa-loop-ch.c
+++ b/gcc/tree-ssa-loop-ch.c
@@ -143,6 +143,27 @@ should_duplicate_loop_header_p (basic_block header, struct loop *loop,
   return true;
 }
 
+/* Return TRUE if LOOP's inner loop is versioned by loop distribution and
+   the guarding internal function call happens to be in LOOP's header.
+   Given loop distribution is placed between pass_ch and pass_ch_vect,
+   this function only returns true in pass_ch_vect.  When it returns TRUE,
+   it's known that copying LOOP's header is meaningless.  */
+
+static bool
+inner_loop_distributed_p (struct loop *loop)
+{
+  gimple *stmt = last_stmt (loop->header);
+  if (stmt == NULL || gimple_code (stmt) != GIMPLE_COND)
+    return false;
+
+  gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
+  gsi_prev (&gsi);
+  if (gsi_end_p (gsi))
+    return false;
+
+  return (gimple_call_internal_p (gsi_stmt (gsi), IFN_LOOP_DIST_ALIAS));
+}
+
 /* Checks whether LOOP is a do-while style loop.  */
 
 static bool
@@ -442,6 +463,9 @@ pass_ch_vect::process_loop_p (struct loop *loop)
   if (loop->dont_vectorize)
     return false;
 
+  if (inner_loop_distributed_p (loop))
+    return false;
+
   if (!do_while_loop_p (loop))
     return true;