re PR tree-optimization/19624 (PRE pessimizes ivopts)

2005-01-30  Daniel Berlin  <dberlin@dberlin.org>

	Fix PR tree-optimization/19624

	* Makefile.in (tree-ssa-pre.o): Add CFGLOOP_H.
	* tree-ssa-pre.c: Add cfgloop.h.
	Update comment.
	(pre_stats): New member, constified.
	(inserted_exprs): New static variable.
	(NECESSARY): New macro.
	(create_expression_by_pieces): Fold the expression, and
	mark it as defaulting to not necessary. Also put in
	inserted_exprs.
	(fully_constant_expression): New function.
	(insert_into_preds_of_block): Modify to not insert phis when we
	are playing with induction variables.
	Push phis onto the inserted_exprs vector, and mark them as not
	necessary by default.
	(insert_aux): Call fully_constant_expression on eprime.
	If all edges produce the same value, mark it constant.
	(mark_operand_necessary): New function.
	(remove_dead_inserted_code): New function.
	(init_pre): Init loop optimizer to get loop info.
	(fini_pre): Free loop_optimizer, and inserted_exprs vec.
	(execute_pre): Commit edge inserts, then remove dead code.

From-SVN: r94448

gcc/Makefile.in

@@ -1663,7 +1663,7 @@ tree-ssa-copyrename.o : tree-ssa-copyrename.c $(TREE_FLOW_H) $(CONFIG_H) \
 tree-ssa-pre.o : tree-ssa-pre.c $(TREE_FLOW_H) $(CONFIG_H) \
    $(SYSTEM_H) $(TREE_H) $(TM_P_H) $(EXPR_H) \
    $(GGC_H) output.h diagnostic.h errors.h toplev.h $(TIMEVAR_H) \
-   $(TM_H) coretypes.h $(TREE_DUMP_H) tree-pass.h $(FLAGS_H)
+   $(TM_H) coretypes.h $(TREE_DUMP_H) tree-pass.h $(FLAGS_H) $(CFGLOOP_H)
 tree-vn.o : tree-vn.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(GGC_H) \
    $(TREE_H) $(TREE_FLOW_H) $(HASHTAB_H) langhooks.h tree-pass.h \
    $(TREE_DUMP_H) diagnostic.h

gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-4.c

+/* { dg-do compile } */ 
+/* { dg-options "-O2 -fdump-tree-pre-stats" } */
+int main(void)
+{
+	int x, c, y;
+	x = 3;
+	if (c)
+		x = 2;
+	y = x + 1;
+	return y;
+}
+/* We should eliminate the x+1 computation from this routine, replacing
+   it with a phi of 3, 4 */
+/* { dg-final { scan-tree-dump-times "Eliminated:1" 1 "pre"} } */

gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-5.c

+/* { dg-do compile } */ 
+/* { dg-options "-O2 -fdump-tree-pre-stats" } */
+int 
+foo (int i)
+{
+	int a, b;
+	if (i)
+		a = 3, b = 2;
+	else
+		a = 2, b = 3;
+	return a + b;
+}
+/* We should detect that a+b is the same along both edges, and replace it with
+   5  */
+/* { dg-final { scan-tree-dump-times "Constified:1" 1 "pre"} } */

gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-6.c

+/* { dg-do compile } */ 
+/* { dg-options "-O2 -fdump-tree-pre-stats" } */
+int main(int x)
+{
+	int c, y;
+	if (c)
+		x = 2;
+	y = x + 1;
+	return y;
+}
+/* We should eliminate one evaluation of x + 1 along the x = 2 path,
+   causing one elimination.  */
+/* { dg-final { scan-tree-dump-times "Eliminated:1" 1 "pre"} } */