This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]
Other format:	[Raw text]

Re: [C PATCH] Discard P - (P + CST) optimization in pointer_diff (PR c/61240)

From: Marc Glisse <marc dot glisse at inria dot fr>
To: Marek Polacek <polacek at redhat dot com>
Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, "Joseph S. Myers" <joseph at codesourcery dot com>, Richard Biener <rguenther at suse dot de>, Jakub Jelinek <jakub at redhat dot com>
Date: Mon, 4 Aug 2014 12:45:48 +0200 (CEST)
Subject: Re: [C PATCH] Discard P - (P + CST) optimization in pointer_diff (PR c/61240)
Authentication-results: sourceware.org; auth=none
References: <20140804101856 dot GB24292 at redhat dot com>
Reply-to: gcc-patches at gcc dot gnu dot org

On Mon, 4 Aug 2014, Marek Polacek wrote:

+/* { dg-do compile } */
+
+void
+foo (void)
+{
+  volatile __PTRDIFF_TYPE__ t;
+  int i;
+  int *p = &i;
+  int *q = &i + 1;
+  t = q - (q - 1);
+  t = (q - 1) - q; /* { dg-warning "integer overflow in expression" } */
+  t = p - (p - 1);
+  t = (p - 1) - p ; /* { dg-warning "integer overflow in expression" } */
+}

Why do you want a warning for (q - 1) - q ? It looks like a perfectlycorrect way to say -1 to me (ptrdiff_t is a signed type for a reason).


--
Marc Glisse

Follow-Ups:
- Re: [C PATCH] Discard P - (P + CST) optimization in pointer_diff (PR c/61240)
  - From: Richard Biener

References:
- [C PATCH] Discard P - (P + CST) optimization in pointer_diff (PR c/61240)
  - From: Marek Polacek

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]