Use max_loop_iterations in transform_to_exit_first_loop_alt

2015-06-30  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/66652
	* tree-parloops.c (try_transform_to_exit_first_loop_alt): Use
	max_loop_iterations to determine if nit + 1 overflows.

	* testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c (f): Rewrite
	using restrict pointers.
	(main): Add arguments to calls to f.
	* testsuite/libgomp.c/parloops-exit-first-loop-alt.c: Same.

	* gcc.dg/parloops-exit-first-loop-alt-pr66652.c: New test.
	* gcc.dg/parloops-exit-first-loop-alt-3.c (f):  Rewrite using restrict
	pointers.
	* gcc.dg/parloops-exit-first-loop-alt.c: Same.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@225162 138bc75d-0d04-0410-961f-82ee72b054a4

6 files changed, 84 insertions, 13 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 00954b1ef08..9b8c7cff399 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2015-06-30  Tom de Vries  <tom@codesourcery.com>
+
+	PR tree-optimization/66652
+	* tree-parloops.c (try_transform_to_exit_first_loop_alt): Use
+	max_loop_iterations to determine if nit + 1 overflows.
+
 2015-06-30  Richard Biener  <rguenther@suse.de>
 
 	* tree-vrp.c (register_edge_assert_for_2): Also register
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 9c2f20b2c72..f249a7d7ded 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2015-06-30  Tom de Vries  <tom@codesourcery.com>
+
+	PR tree-optimization/66652
+	* gcc.dg/parloops-exit-first-loop-alt-pr66652.c: New test.
+	* gcc.dg/parloops-exit-first-loop-alt-3.c (f):  Rewrite using restrict
+	pointers.
+	* gcc.dg/parloops-exit-first-loop-alt.c: Same.
+
 2015-06-29  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/65977
diff --git a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c
index b0fde372a14..fec53a19628 100644
--- a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c
+++ b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c
@@ -7,7 +7,7 @@
 unsigned int *a;
 
 unsigned int
-f (unsigned int n)
+f (unsigned int n, unsigned int *__restrict__ a)
 {
   int i;
   unsigned int sum = 1;
diff --git a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-pr66652.c b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-pr66652.c
new file mode 100644
index 00000000000..2ea097d06f9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-pr66652.c
@@ -0,0 +1,31 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target pthread } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2 -fdump-tree-parloops" } */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+
+unsigned int
+f (unsigned int n, unsigned int sum)
+{
+  unsigned int i;
+
+  i = UINT_MAX;
+  do
+    {
+      sum += i % 13;
+      i++;
+    }
+  while (i < n - 1);
+
+  return sum;
+}
+
+/* Four times % 13:
+   - once in f._loopfn.0
+   - once in the parallel
+   - once in the low iteration count loop
+   - once for a peeled off last iteration following the parallel.
+   In other words, we want try_transform_to_exit_first_loop_alt to fail.  */
+/* { dg-final { scan-tree-dump-times "(?n)% 13" 4 "parloops" } } */
diff --git a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c
index b36f01b8f8f..e088fa110b3 100644
--- a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c
+++ b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c
@@ -4,14 +4,9 @@
 
 /* Variable bound, vector addition.  */
 
-#define N 1000
-
-unsigned int a[N];
-unsigned int b[N];
-unsigned int c[N];
-
 void
-f (unsigned int n)
+f (unsigned int n, unsigned int *__restrict__ a, unsigned int *__restrict__ b,
+   unsigned int *__restrict__ c)
 {
   int i;
 
@@ -19,9 +14,9 @@ f (unsigned int n)
     c[i] = a[i] + b[i];
 }
 
-/* Three times three array accesses:
-   - three in f._loopfn.0
-   - three in the parallel
-   - three in the low iteration count loop
+/* Three times a store:
+   - one in f._loopfn.0
+   - one in the parallel
+   - one in the low iteration count loop
    Crucially, none for a peeled off last iteration following the parallel.  */
-/* { dg-final { scan-tree-dump-times "(?n)\\\[i" 9 "parloops" } } */
+/* { dg-final { scan-tree-dump-times "(?n)^  \\*_\[0-9\]*" 3 "parloops" } } */
diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c
index ec708c67ac9..21ed17b4caf 100644
--- a/gcc/tree-parloops.c
+++ b/gcc/tree-parloops.c
@@ -1801,8 +1801,39 @@ try_transform_to_exit_first_loop_alt (struct loop *loop,
 
   gcc_assert (TREE_CODE (nit) == SSA_NAME);
 
+  /* Variable nit is the loop bound as returned by canonicalize_loop_ivs, for an
+     iv with base 0 and step 1 that is incremented in the latch, like this:
+
+     <bb header>:
+     # iv_1 = PHI <0 (preheader), iv_2 (latch)>
+     ...
+     if (iv_1 < nit)
+       goto <bb latch>;
+     else
+       goto <bb exit>;
+
+     <bb latch>:
+     iv_2 = iv_1 + 1;
+     goto <bb header>;
+
+     The range of iv_1 is [0, nit].  The latch edge is taken for
+     iv_1 == [0, nit - 1] and the exit edge is taken for iv_1 == nit.  So the
+     number of latch executions is equal to nit.
+
+     The function max_loop_iterations gives us the maximum number of latch
+     executions, so it gives us the maximum value of nit.  */
+  widest_int nit_max;
+  if (!max_loop_iterations (loop, &nit_max))
+    return false;
+
+  /* Check if nit + 1 overflows.  */
+  widest_int type_max = wi::to_widest (TYPE_MAXVAL (nit_type));
+  if (!wi::lts_p (nit_max, type_max))
+    return false;
+
   gimple def = SSA_NAME_DEF_STMT (nit);
 
+  /* Try to find nit + 1, in the form of n in an assignment nit = n - 1.  */
   if (def
       && is_gimple_assign (def)
       && gimple_assign_rhs_code (def) == PLUS_EXPR)