Jonathan Lennox - Re: PATCH RFC: -Wstrict-overflow, take 2 (original) (raw)

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• From: Jonathan Lennox
• To: Ian Lance Taylor
• Cc: gcc-patches at gcc dot gnu dot org
• Date: Fri, 16 Feb 2007 17:15:13 -0500
• Subject: Re: PATCH RFC: -Wstrict-overflow, take 2
• References: <m3hctwgi1d.fsf@localhost.localdomain> <17878.7709.414766.597566@metro-north.cs.columbia.edu> <m3mz3ddc9q.fsf@localhost.localdomain>

On February 16 2007, "Ian Lance Taylor" wrote to "Jonathan Lennox, gcc-patches@gcc.gnu.org" saying:

Jonathan Lennox lennox@cs.columbia.edu writes:

How hard would it be to change this diagnostic to print the actual values of "X", "+-", "C1", "cmp", and "C2"?

For expmed.c:3485, for example, the warning would be

../../trunk/gcc/expmed.c:3485: warning: assuming signed overflow does not occur when changing "size - 1 < 32" to "size < 32 + 1"

I think this would be much more accessible to people not versed in the intricacies of compilers, and also make it much easier (as in this case) to see at a glance if signed overflow could actually be a problem.

Well, the X can, in general, be anything. As far as I know we don't have a good way to dump general expressions in warning contexts. But maybe I just don't know about it.

The C1 and C2 are integer constants, and would be easy to dump. It's line 8296 of fold-const.c. Go for it.

The tricky points are that a) fold_overflow_warning doesn't take a formatting string, and b) I don't have a GCC copyright assignment, and my current work situation would make it non-trivial to acquire one.

I could file an enhancement request PR, I suppose.

-- Jonathan Lennox lennox at cs dot columbia dot edu

• References:
  • PATCH RFC: -Wstrict-overflow, take 2
    * From: Ian Lance Taylor
  • Re: PATCH RFC: -Wstrict-overflow, take 2
    * From: Jonathan Lennox
  • Re: PATCH RFC: -Wstrict-overflow, take 2
    * From: Ian Lance Taylor