This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
[patch] fold-const.c: Fix tree-optimization/16632.
- From: Kazu Hirata <kazu at cs dot umass dot edu>
- To: gcc-patches at gcc dot gnu dot org
- Date: Sun, 03 Oct 2004 10:15:31 -0400 (EDT)
- Subject: [patch] fold-const.c: Fix tree-optimization/16632.
Hi,
Attached is a patch to fix tree-optimization/16632.
Consider
int
bar (int i)
{
if ((i & 4) == 2)
return 1;
return 0;
}
Note that the condition inside the "if" statement is always false, but
unfortunately fold() fails to see that, and the "if" statement
survives through all the tree optimizations.
Let C be the constant on the left in the condition, which is 4 in the
example above. Let D be the constant on the right. In general, we
can fold (i & C) != D into 0 if D & ~C != 0. Without this patch,
fold() does not fold ~C, failing to see that D & ~C != 0.
The patch fixes the problem by telling fold() to fold ~C.
It also fixes a similar problem where | is used instead of &.
I've attached a testcase, but I am wondering if it's OK to add a
fold()-related testcase into the tree-ssa area of the testsuite.
Could somebody clarify this for me?
Tested on i686-pc-linux-gnu. OK to apply?
Kazu Hirata
2004-10-03 Kazu Hirata <kazu@cs.umass.edu>
* fold-const.c (fold) [EQ_EXPR]: When seeing if D & ~C != 0 to
fold (A & C) == D into 0, fold ~C. Similarly, for the case
where | is used instead of &.
2004-10-03 Kazu Hirata <kazu@cs.umass.edu>
* gcc.dg/tree-ssa/20041002-1.c: New.
Index: fold-const.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fold-const.c,v
retrieving revision 1.465
diff -u -r1.465 fold-const.c
--- fold-const.c 29 Sep 2004 19:44:53 -0000 1.465
+++ fold-const.c 2 Oct 2004 12:36:08 -0000
@@ -8400,11 +8400,11 @@
&& TREE_CODE (arg1) == INTEGER_CST
&& TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
{
- tree dandnotc
- = fold (build2 (BIT_AND_EXPR, TREE_TYPE (arg0),
- arg1, build1 (BIT_NOT_EXPR,
- TREE_TYPE (TREE_OPERAND (arg0, 1)),
- TREE_OPERAND (arg0, 1))));
+ tree notc = fold (build1 (BIT_NOT_EXPR,
+ TREE_TYPE (TREE_OPERAND (arg0, 1)),
+ TREE_OPERAND (arg0, 1)));
+ tree dandnotc = fold (build2 (BIT_AND_EXPR, TREE_TYPE (arg0),
+ arg1, notc));
tree rslt = code == EQ_EXPR ? integer_zero_node : integer_one_node;
if (integer_nonzerop (dandnotc))
return omit_one_operand (type, rslt, arg0);
@@ -8417,10 +8417,9 @@
&& TREE_CODE (arg1) == INTEGER_CST
&& TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
{
- tree candnotd
- = fold (build2 (BIT_AND_EXPR, TREE_TYPE (arg0),
- TREE_OPERAND (arg0, 1),
- build1 (BIT_NOT_EXPR, TREE_TYPE (arg1), arg1)));
+ tree notd = fold (build1 (BIT_NOT_EXPR, TREE_TYPE (arg1), arg1));
+ tree candnotd = fold (build2 (BIT_AND_EXPR, TREE_TYPE (arg0),
+ TREE_OPERAND (arg0, 1), notd));
tree rslt = code == EQ_EXPR ? integer_zero_node : integer_one_node;
if (integer_nonzerop (candnotd))
return omit_one_operand (type, rslt, arg0);
--- /dev/null 2004-02-23 16:02:56.000000000 -0500
+++ testsuite/gcc.dg/tree-ssa/20041002-1.c 2004-10-02 08:35:16.969652951 -0400
@@ -0,0 +1,23 @@
+/* PR tree-optimization/16632
+ fold() failed to see the following "if" statements never trigger. */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ssa" } */
+
+int
+foo (int i)
+{
+ if ((i | 3) == 1)
+ return 1;
+ return 0;
+}
+
+int
+bar (int i)
+{
+ if ((i & 4) == 2)
+ return 1;
+ return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "if" 0 "ssa" } } */