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Re: Small optimization patch
- From: "Joseph S. Myers" <jsm28 at cam dot ac dot uk>
- To: Steve Ellcey <sje at cup dot hp dot com>
- Cc: <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 12 Feb 2002 21:36:52 +0000 (GMT)
- Subject: Re: Small optimization patch
On Tue, 12 Feb 2002, Steve Ellcey wrote:
> OK, I understand now. It looks like my change would make a valid
> warning disappear with optimization and I agree that that is a bad
> thing. It looks like this is because we already incorrectly don't give
> an error if we use "(char) 5" in the switch. I'll look into it more
> later.
"(char) 5" is an integer constant expression, which is OK. The current
problems are such as "FIVE + FIVE" and "+FIVE". I've applied the
following patch to mainline to add tests indicating the various cases we
get right and wrong. I'll submit a PR corresponding to the XFAILs.
2002-02-12 Joseph S. Myers <jsm28@cam.ac.uk>
* gcc.dg/c90-const-expr-3.c, gcc.dg/c99-const-expr-3.c: New tests.
--- /dev/null Mon Mar 26 23:57:02 2001
+++ c90-const-expr-3.c Tue Feb 12 17:55:38 2002
@@ -0,0 +1,39 @@
+/* Test for constant expressions: broken optimization with const variables. */
+/* Origin: Joseph Myers <jsm28@cam.ac.uk> */
+/* { dg-do compile } */
+/* { dg-options "-std=iso9899:1990 -O2" } */
+/* Note: not using -pedantic since the -std option alone should be enough
+ to give the correct behavior to conforming programs. */
+
+static const int ZERO = 0;
+
+int *a;
+int b;
+long *c;
+
+/* Assertion that n is a constant zero: so the conditional expression
+ has type 'int *' instead of 'void *'.
+*/
+#define ASSERT_NPC(n) (b = *(1 ? a : (n)))
+/* Assertion that n is not a constant zero: so the conditional
+ expresions has type 'void *' instead of 'int *'.
+*/
+#define ASSERT_NOT_NPC(n) (c = (1 ? a : (void *)(__SIZE_TYPE__)(n)))
+
+void
+foo (void)
+{
+ ASSERT_NPC (0);
+ ASSERT_NOT_NPC (ZERO);
+ ASSERT_NPC (0 + 0);
+ ASSERT_NOT_NPC (ZERO + 0); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NOT_NPC (ZERO + ZERO); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NPC (+0);
+ ASSERT_NOT_NPC (+ZERO); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NPC (-0);
+ ASSERT_NOT_NPC (-ZERO); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NPC ((char) 0);
+ ASSERT_NOT_NPC ((char) ZERO);
+ ASSERT_NPC ((int) 0);
+ ASSERT_NOT_NPC ((int) ZERO);
+}
--- /dev/null Mon Mar 26 23:57:02 2001
+++ c99-const-expr-3.c Tue Feb 12 17:57:24 2002
@@ -0,0 +1,39 @@
+/* Test for constant expressions: broken optimization with const variables. */
+/* Origin: Joseph Myers <jsm28@cam.ac.uk> */
+/* { dg-do compile } */
+/* { dg-options "-std=iso9899:1999 -O2" } */
+/* Note: not using -pedantic since the -std option alone should be enough
+ to give the correct behavior to conforming programs. */
+
+static const int ZERO = 0;
+
+int *a;
+int b;
+long *c;
+
+/* Assertion that n is a constant zero: so the conditional expression
+ has type 'int *' instead of 'void *'.
+*/
+#define ASSERT_NPC(n) (b = *(1 ? a : (n)))
+/* Assertion that n is not a constant zero: so the conditional
+ expresions has type 'void *' instead of 'int *'.
+*/
+#define ASSERT_NOT_NPC(n) (c = (1 ? a : (void *)(__SIZE_TYPE__)(n)))
+
+void
+foo (void)
+{
+ ASSERT_NPC (0);
+ ASSERT_NOT_NPC (ZERO);
+ ASSERT_NPC (0 + 0);
+ ASSERT_NOT_NPC (ZERO + 0); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NOT_NPC (ZERO + ZERO); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NPC (+0);
+ ASSERT_NOT_NPC (+ZERO); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NPC (-0);
+ ASSERT_NOT_NPC (-ZERO); /* { dg-bogus "incompatible" "bogus null pointer constant" { xfail *-*-* } } */
+ ASSERT_NPC ((char) 0);
+ ASSERT_NOT_NPC ((char) ZERO);
+ ASSERT_NPC ((int) 0);
+ ASSERT_NOT_NPC ((int) ZERO);
+}
--
Joseph S. Myers
jsm28@cam.ac.uk