loop-split improvements, part 1

[Jan Hubicka via Gcc-patches]

Hi,
while looking on profile misupdate on hmmer I noticed that loop splitting pass 
is not
able to handle the loop it has as an example it should apply on:

   One transformation of loops like:

   for (i = 0; i < 100; i++)
     {
       if (i < 50)
         A;
       else
         B;
     }

   into:

   for (i = 0; i < 50; i++)
     {
       A;
     }
   for (; i < 100; i++)
     {
       B;
     }

The problem is that ivcanon turns the test into i != 100 and the pass
explicitly gives up on any loops ending with != test.  It needs to know
the directoin of the induction variable in order to derive right conditions,
but that can be done also from step.

It turns out that there are no testcases for basic loop splitting.  I will add
some with the profile update fix.

There are other issues, like VRP will turn i < 99 into i == 99 based on
value range which also makes the pass to give up.

Bootstrapped/regtested x86_64-linux, OK?

gcc/ChangeLog:

        * tree-ssa-loop-split.cc (split_loop): Also support NE driven
        loops when IV test is not overflowing.

gcc/testsuite/ChangeLog:

        * gcc.dg/tree-ssa/ifc-12.c: Disable loop splitting.
        * gcc.target/i386/avx2-gather-6.c: Likewise.
        * gcc.target/i386/avx2-vect-aggressive.c: Likewise.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c 
b/gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c
index 9468c070489..bedf29c7dbc 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-Ofast -fdump-tree-ifcvt-stats-blocks-details" } */
+/* { dg-options "-Ofast -fdump-tree-ifcvt-stats-blocks-details 
-fno-split-loops" } */
 /* { dg-require-visibility "" } */
 
 struct st
diff --git a/gcc/testsuite/gcc.target/i386/avx2-gather-6.c 
b/gcc/testsuite/gcc.target/i386/avx2-gather-6.c
index b9119581ae2..47a95dbe989 100644
--- a/gcc/testsuite/gcc.target/i386/avx2-gather-6.c
+++ b/gcc/testsuite/gcc.target/i386/avx2-gather-6.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O3 -mavx2 -fno-common -fdump-tree-vect-details 
-mtune=skylake" } */
+/* { dg-options "-O3 -mavx2 -fno-common -fdump-tree-vect-details 
-mtune=skylake -fno-split-loops" } */
 
 #include "avx2-gather-5.c"
 
diff --git a/gcc/testsuite/gcc.target/i386/avx2-vect-aggressive.c 
b/gcc/testsuite/gcc.target/i386/avx2-vect-aggressive.c
index 57192791857..fa336e70e84 100644
--- a/gcc/testsuite/gcc.target/i386/avx2-vect-aggressive.c
+++ b/gcc/testsuite/gcc.target/i386/avx2-vect-aggressive.c
@@ -1,6 +1,6 @@
 /* { dg-do run } */
 /* { dg-require-effective-target avx2 } */
-/* { dg-options "-mavx2 -O3 -fopenmp-simd -fdump-tree-vect-details 
-fdisable-tree-thread1" } */
+/* { dg-options "-mavx2 -O3 -fopenmp-simd -fdump-tree-vect-details 
-fdisable-tree-thread1 -fno-split-loops" } */
 
 #include "avx2-check.h"
 #define N 64
diff --git a/gcc/tree-ssa-loop-split.cc b/gcc/tree-ssa-loop-split.cc
index b41b5e614c2..27780370d85 100644
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -540,10 +545,17 @@ split_loop (class loop *loop1)
       || !empty_block_p (loop1->latch)
       || !easy_exit_values (loop1)
       || !number_of_iterations_exit (loop1, exit1, &niter, false, true)
-      || niter.cmp == ERROR_MARK
-      /* We can't yet handle loops controlled by a != predicate.  */
-      || niter.cmp == NE_EXPR)
+      || niter.cmp == ERROR_MARK)
     return false;
+  if (niter.cmp == NE_EXPR)
+    {
+      if (!niter.control.no_overflow)
+       return false;
+      if (tree_int_cst_sign_bit (niter.control.step) > 0)
+       niter.cmp = GT_EXPR;
+      else
+       niter.cmp = LT_EXPR;
+    }
 
   bbs = get_loop_body (loop1);