[gcc r14-2834] loop-split improvements, part 1

[gcc r14-2834] loop-split improvements, part 1

[Jan Hubicka]

https://gcc.gnu.org/g:b9d7140c80bd3c7355b8291bb46f0895dcd8c3cb

commit r14-2834-gb9d7140c80bd3c7355b8291bb46f0895dcd8c3cb
Author: Jan Hubicka <jh@suse.cz>
Date:   Fri Jul 28 09:16:09 2023 +0200

    loop-split improvements, part 1
    
    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.
    
    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:
---
 gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c               |  2 +-
 gcc/testsuite/gcc.target/i386/avx2-gather-6.c        |  2 +-
 gcc/testsuite/gcc.target/i386/avx2-vect-aggressive.c |  2 +-
 gcc/tree-ssa-loop-split.cc                           | 13 ++++++++++---
 4 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c b/gcc/testsuite/gcc.dg/tree-ssa/ifc-12.c
index 9468c070489..7f09c381d9f 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..f441f3fe1b5 100644
--- a/gcc/tree-ssa-loop-split.cc
+++ b/gcc/tree-ssa-loop-split.cc
@@ -540,10 +540,17 @@ 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);