re PR tree-optimization/60098 (DSE fails to DSE errno settings)

2014-06-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/60098
	* tree-ssa-dse.c (dse_possible_dead_store_p): Walk until
	we hit a kill.
	(dse_optimize_stmt): Simplify, now that we found a kill
	earlier.

	* gcc.dg/tree-ssa/ssa-dse-15.c: New testcase.

From-SVN: r211224

gcc/ChangeLog

 2014-06-04  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/60098
+	* tree-ssa-dse.c (dse_possible_dead_store_p): Walk until
+	we hit a kill.
+	(dse_optimize_stmt): Simplify, now that we found a kill
+	earlier.
+
+2014-06-04  Richard Biener  <rguenther@suse.de>
+
 	* tree-ssa-alias.c (stmt_may_clobber_ref_p): Improve handling
 	of accesses with non-invariant address.
 

gcc/testsuite/ChangeLog

 2014-06-04  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/60098
+	* gcc.dg/tree-ssa/ssa-dse-15.c: New testcase.
+
+2014-06-04  Richard Biener  <rguenther@suse.de>
+
 	* gcc.dg/tree-ssa/ssa-dse-16.c: New testcase.
 
 2014-06-04  Igor Zamyatin  <igor.zamyatin@intel.com>

gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-15.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-dse1-details" } */
+
+void *foo (int *p)
+{
+  void *q;
+  /* We should be able to DSE this store (p may point to errno).  */
+  *p = 0;
+  q = __builtin_malloc (4);
+  *p = 0;
+  return q;
+}
+
+int j;
+void bar (int *i)
+{
+  /* This store is dead as well.  */
+  j = 1;
+  *i = 0;
+  j = 2;
+}
+
+/* { dg-final { scan-tree-dump-times "Deleted dead store" 2 "dse1" } } */
+/* { dg-final { cleanup-tree-dump "dse1" } } */

gcc/tree-ssa-dse.c

@@ -198,10 +198,8 @@ dse_possible_dead_store_p (gimple stmt, gimple *use_stmt)
 	  break;
 	}
     }
-  /* We deliberately stop on clobbering statements and not only on
-     killing ones to make walking cheaper.  Otherwise we can just
-     continue walking until both stores have equal reference trees.  */
-  while (!stmt_may_clobber_ref_p (temp, gimple_assign_lhs (stmt)));
+  /* Continue walking until we reach a kill.  */
+  while (!stmt_kills_ref_p (temp, gimple_assign_lhs (stmt)));
 
   *use_stmt = temp;
 
@@ -248,21 +246,14 @@ dse_optimize_stmt (gimple_stmt_iterator *gsi)
       if (!dse_possible_dead_store_p (stmt, &use_stmt))
 	return;
 
+      /* Now we know that use_stmt kills the LHS of stmt.  */
+
       /* But only remove *this_2(D) ={v} {CLOBBER} if killed by
 	 another clobber stmt.  */
       if (gimple_clobber_p (stmt)
 	  && !gimple_clobber_p (use_stmt))
 	return;
 
-      /* If we have precisely one immediate use at this point and the
-	 stores are to the same memory location or there is a chain of
-	 virtual uses from stmt and the stmt which stores to that same
-	 memory location, then we may have found redundant store.  */
-      if ((gimple_has_lhs (use_stmt)
-	   && (operand_equal_p (gimple_assign_lhs (stmt),
-				gimple_get_lhs (use_stmt), 0)))
-	  || stmt_kills_ref_p (use_stmt, gimple_assign_lhs (stmt)))
-	{
       basic_block bb;
 
       /* If use_stmt is or might be a nop assignment, e.g. for
@@ -299,7 +290,6 @@ dse_optimize_stmt (gimple_stmt_iterator *gsi)
 	 SSA_NAME manager.  */
       release_defs (stmt);
     }
-    }
 }
 
 class dse_dom_walker : public dom_walker