tree-optimization/111294 - better DCE after forwprop

The following adds more aggressive DCE to forwprop to clean up dead
stmts when folding a stmt leaves some operands unused.  The patch
uses simple_dce_from_worklist for this purpose, queueing original
operands before substitution and folding, but only if we folded the
stmt.

This removes one dead stmt biasing threading costs in a later pass
but it doesn't resolve the optimization issue in the PR yet.

	PR tree-optimization/111294
	* tree-ssa-forwprop.cc (pass_forwprop::execute): Track
	operands that eventually become dead and use simple_dce_from_worklist
	to remove their definitions if they did so.

	* gcc.dg/tree-ssa/evrp10.c: Adjust.
	* gcc.dg/tree-ssa/evrp6.c: Likewise.
	* gcc.dg/tree-ssa/forwprop-31.c: Likewise.
	* gcc.dg/tree-ssa/neg-cast-3.c: Likewise.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c b/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c
index 6ca00e4adaa2af55a981afaa3f22388401622151..776c80c684f0df7db38e721bec347d2862d95678 100644 (file)
--- a/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp10.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-evrp" }*/
+/* { dg-options "-O2 -fdump-tree-evrp -fno-tree-forwprop" }*/
 
 typedef __INT32_TYPE__ int32_t;
 

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/evrp6.c b/gcc/testsuite/gcc.dg/tree-ssa/evrp6.c
index aaeec68866e25758387936e2da2f14de96950441..0f9561b6a72b9736ea213d118f2eb301907abfe0 100644 (file)
--- a/gcc/testsuite/gcc.dg/tree-ssa/evrp6.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/evrp6.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-evrp-details" } */
+/* { dg-options "-O2 -fdump-tree-evrp-details -fdump-tree-mergephi1" } */
 
 extern void abort (void);
 
@@ -18,4 +18,5 @@ foo (int k, int j)
 
   return j;
 }
-/* { dg-final { scan-tree-dump "\\\[12, \\+INF" "evrp" } } */
+/* { dg-final { scan-tree-dump "\\\[11, \\+INF" "evrp" } } */
+/* { dg-final { scan-tree-dump-not "abort" "mergephi1" } } */

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-31.c b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-31.c
index edf8026488406718222298216c5cf460bd36fe72..40cc86383fa9867e410e98acbff532d1741e2f32 100644 (file)
--- a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-31.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-31.c
@@ -9,6 +9,5 @@ int foo (int x)
   return w - z; /* becomes 0 */
 }
 
-/* Only z = x + 1 is retained.  */
-/* { dg-final { scan-tree-dump-times " = " 1 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times " = " 0 "forwprop1" } } */
 /* { dg-final { scan-tree-dump "return 0;" "forwprop1" } } */

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-3.c b/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-3.c
index 7b23ca85d1f9a54ac9d25e4d702b55a958142cbc..61b89403a9372b5946cebf52e0fc0dc0856884e4 100644 (file)
--- a/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-3.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/neg-cast-3.c
@@ -10,6 +10,4 @@ unsigned f(_Bool a)
 }
 
 /* There should be no cast to int at all. */
-/* Forwprop1 does not remove all of the statements. */
-/* { dg-final { scan-tree-dump-not "\\\(int\\\)" "forwprop1" { xfail *-*-* } } } */
-/* { dg-final { scan-tree-dump-not "\\\(int\\\)" "optimized" } } */
+/* { dg-final { scan-tree-dump-not "\\\(int\\\)" "forwprop1" } } */

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 94ca47a9726da2e7492848c82a306be09a9ec412..d4e9202a2d46127b49d2d834e7323e31c210ac83 100644 (file)
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -53,6 +53,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cgraph.h"
 #include "tree-ssa.h"
 #include "gimple-range.h"
+#include "tree-ssa-dce.h"
 
 /* This pass propagates the RHS of assignment statements into use
    sites of the LHS of the assignment.  It's basically a specialized
@@ -3502,8 +3503,9 @@ pass_forwprop::execute (function *fun)
     |= EDGE_EXECUTABLE;
   auto_vec<gimple *, 4> to_fixup;
   auto_vec<gimple *, 32> to_remove;
+  auto_bitmap simple_dce_worklist;
+  auto_bitmap need_ab_cleanup;
   to_purge = BITMAP_ALLOC (NULL);
-  bitmap need_ab_cleanup = BITMAP_ALLOC (NULL);
   for (int i = 0; i < postorder_num; ++i)
     {
       gimple_stmt_iterator gsi;
@@ -3902,10 +3904,14 @@ pass_forwprop::execute (function *fun)
            {
              tree use = USE_FROM_PTR (usep);
              tree val = fwprop_ssa_val (use);
-             if (val && val != use && may_propagate_copy (use, val))
+             if (val && val != use)
                {
-                 propagate_value (usep, val);
-                 substituted_p = true;
+                 bitmap_set_bit (simple_dce_worklist, SSA_NAME_VERSION (use));
+                 if (may_propagate_copy (use, val))
+                   {
+                     propagate_value (usep, val);
+                     substituted_p = true;
+                   }
                }
            }
          if (substituted_p
@@ -3925,6 +3931,11 @@ pass_forwprop::execute (function *fun)
                                   && gimple_call_noreturn_p (stmt));
              changed = false;
 
+             auto_vec<tree, 8> uses;
+             FOR_EACH_SSA_USE_OPERAND (usep, stmt, iter, SSA_OP_USE)
+               if (uses.space (1))
+                 uses.quick_push (USE_FROM_PTR (usep));
+
              if (fold_stmt (&gsi, fwprop_ssa_val))
                {
                  changed = true;
@@ -3935,6 +3946,12 @@ pass_forwprop::execute (function *fun)
                    if (gimple_cond_true_p (cond)
                        || gimple_cond_false_p (cond))
                      cfg_changed = true;
+                 /* Queue old uses for simple DCE.  */
+                 for (tree use : uses)
+                   if (TREE_CODE (use) == SSA_NAME
+                       && !SSA_NAME_IS_DEFAULT_DEF (use))
+                     bitmap_set_bit (simple_dce_worklist,
+                                     SSA_NAME_VERSION (use));
                }
 
              if (changed || substituted_p)
@@ -4115,6 +4132,7 @@ pass_forwprop::execute (function *fun)
          release_defs (stmt);
        }
     }
+  simple_dce_from_worklist (simple_dce_worklist, to_purge);
 
   /* Fixup stmts that became noreturn calls.  This may require splitting
      blocks and thus isn't possible during the walk.  Do this
@@ -4135,7 +4153,6 @@ pass_forwprop::execute (function *fun)
   cfg_changed |= gimple_purge_all_dead_eh_edges (to_purge);
   cfg_changed |= gimple_purge_all_dead_abnormal_call_edges (need_ab_cleanup);
   BITMAP_FREE (to_purge);
-  BITMAP_FREE (need_ab_cleanup);
 
   if (get_range_query (fun) != get_global_range_query ())
     disable_ranger (fun);