re PR tree-optimization/78343 (Loop is not eliminated)

2016-11-24  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/78343
	* passes.def: Add CD-DCE pass after loop splitting.
	* tree-ssa-dce.c (find_obviously_necessary_stmts): Move
	SCEV init/finalize ...
	(perform_tree_ssa_dce): ... here.  Deal with being
	executed inside the loop pipeline in aggressive mode.

	* gcc.dg/tree-ssa/sccp-2.c: New testcase.
	* gcc.dg/autopar/uns-outer-6.c: Adjust.
	* gcc.dg/tree-ssa/20030808-1.c: Likewise.
	* gcc.dg/tree-ssa/20040305-1.c: Likewise.
	* gcc.dg/vect/pr38529.c: Likewise.

From-SVN: r242872

gcc/ChangeLog

+2016-11-24  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/78343
+	* passes.def: Add CD-DCE pass after loop splitting.
+	* tree-ssa-dce.c (find_obviously_necessary_stmts): Move
+	SCEV init/finalize ...
+	(perform_tree_ssa_dce): ... here.  Deal with being
+	executed inside the loop pipeline in aggressive mode.
+
 2016-11-25  Thomas Preud'homme  <thomas.preudhomme@arm.com>
 
 	* tree-ssa-math-opts.c (struct symbolic_number): Improve comment.

gcc/passes.def

@@ -272,6 +272,9 @@ along with GCC; see the file COPYING3.  If not see
 	  NEXT_PASS (pass_tree_unswitch);
 	  NEXT_PASS (pass_scev_cprop);
 	  NEXT_PASS (pass_loop_split);
+	  /* All unswitching, final value replacement and splitting can expose
+	     empty loops.  Remove them now.  */
+	  NEXT_PASS (pass_cd_dce);
 	  NEXT_PASS (pass_record_bounds);
 	  NEXT_PASS (pass_loop_distribution);
 	  NEXT_PASS (pass_copy_prop);

gcc/testsuite/ChangeLog

+2016-11-24  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/78343
+	* gcc.dg/tree-ssa/sccp-2.c: New testcase.
+	* gcc.dg/autopar/uns-outer-6.c: Adjust.
+	* gcc.dg/tree-ssa/20030808-1.c: Likewise.
+	* gcc.dg/tree-ssa/20040305-1.c: Likewise.
+	* gcc.dg/vect/pr38529.c: Likewise.
+
 2016-11-25  Thomas Preud'homme  <thomas.preudhomme@arm.com>
 
 	PR tree-optimization/77673

gcc/testsuite/gcc.dg/autopar/uns-outer-6.c

@@ -25,7 +25,7 @@ parloop (int N)
   for (i = 0; i < N; i++)
     {
       for (j = 0; j < N; j++)
-	y[i]=x[i][j];
+	y[i] += x[i][j];
       sum += y[i];
     }
   g_sum = sum;

gcc/testsuite/gcc.dg/tree-ssa/20030808-1.c

@@ -33,8 +33,8 @@ delete_dead_jumptables ()
 /* There should be no loads of ->code.  If any exist, then we failed to
    optimize away all the IF statements and the statements feeding
    their conditions.  */
-/* { dg-final { scan-tree-dump-times "->code" 0 "cddce2"} } */
+/* { dg-final { scan-tree-dump-times "->code" 0 "cddce3"} } */
    
 /* There should be no IF statements.  */
-/* { dg-final { scan-tree-dump-times "if " 0 "cddce2"} } */
+/* { dg-final { scan-tree-dump-times "if " 0 "cddce3"} } */
 

gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c

@@ -27,4 +27,4 @@ void foo(int edx, int eax)
 
 /* After cddce we should have two IF statements remaining as the other
    two tests can be threaded.  */
-/* { dg-final { scan-tree-dump-times "if " 2 "cddce2"} } */
+/* { dg-final { scan-tree-dump-times "if " 2 "cddce3"} } */

gcc/testsuite/gcc.dg/tree-ssa/sccp-2.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+unsigned int
+test(unsigned int quant)
+{
+  unsigned int sum = 0;
+  for (unsigned int i = 0; i < quant; ++i)
+    sum += quant;
+  return sum;
+}
+
+/* A single basic-block should remain (computing and
+   returning quant * quant).  */
+/* { dg-final { scan-tree-dump-times "bb" 1 "optimized" } } */

gcc/testsuite/gcc.dg/vect/pr38529.c

@@ -11,7 +11,3 @@ void foo()
     for (j = 0; j < 17; ++j)
       a[i] = 0;
 }
-
-/* { dg-final { scan-tree-dump-times "OUTER LOOP VECTORIZED" 1 "vect"  } } */
-
-

gcc/tree-ssa-dce.c

@@ -400,7 +400,6 @@ find_obviously_necessary_stmts (bool aggressive)
   if (aggressive)
     {
       struct loop *loop;
-      scev_initialize ();
       if (mark_irreducible_loops ())
 	FOR_EACH_BB_FN (bb, cfun)
 	  {
@@ -423,7 +422,6 @@ find_obviously_necessary_stmts (bool aggressive)
 	      fprintf (dump_file, "can not prove finiteness of loop %i\n", loop->num);
 	    mark_control_dependent_edges_necessary (loop->latch, false);
 	  }
-      scev_finalize ();
     }
 }
 
@@ -1567,9 +1565,13 @@ perform_tree_ssa_dce (bool aggressive)
   /* Preheaders are needed for SCEV to work.
      Simple lateches and recorded exits improve chances that loop will
      proved to be finite in testcases such as in loop-15.c and loop-24.c  */
-  if (aggressive)
-    loop_optimizer_init (LOOPS_NORMAL
-			 | LOOPS_HAVE_RECORDED_EXITS);
+  bool in_loop_pipeline = scev_initialized_p ();
+  if (aggressive && ! in_loop_pipeline)
+    {
+      scev_initialize ();
+      loop_optimizer_init (LOOPS_NORMAL
+			   | LOOPS_HAVE_RECORDED_EXITS);
+    }
 
   tree_dce_init (aggressive);
 
@@ -1588,8 +1590,11 @@ perform_tree_ssa_dce (bool aggressive)
 
   find_obviously_necessary_stmts (aggressive);
 
-  if (aggressive)
-    loop_optimizer_finalize ();
+  if (aggressive && ! in_loop_pipeline)
+    {
+      loop_optimizer_finalize ();
+      scev_finalize ();
+    }
 
   longest_chain = 0;
   total_chain = 0;
@@ -1623,7 +1628,7 @@ perform_tree_ssa_dce (bool aggressive)
   if (something_changed)
     {
       free_numbers_of_iterations_estimates (cfun);
-      if (scev_initialized_p ())
+      if (in_loop_pipeline)
 	scev_reset ();
       return TODO_update_ssa | TODO_cleanup_cfg;
     }