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[Bug middle-end/11492] Unsigned char promoted to signed int in for loop test for gpp but not gcc
- From: "manu at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 22 Jan 2007 08:28:13 -0000
- Subject: [Bug middle-end/11492] Unsigned char promoted to signed int in for loop test for gpp but not gcc
- References: <bug-11492-6488@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #6 from manu at gcc dot gnu dot org 2007-01-22 08:28 -------
(In reply to comment #5)
> (In reply to comment #1)
> > "1000" is a signed integer constant, so b*1000 is a signed integer too. I
> > guess the warning is ok, then.
>
> That is only true for unsigned multiplication and signed when overflow is
> undefined (-fno-wrapv which is default for C and C++).
>
But in the example shown, it is true always, since b == 2 at compile time.
Can't we detect that? I know that there is no dataflow solving in the
front-ends. But as you said, tree_expr_nonnegative_p is part of the middle-end.
Perhaps we should have dataflow info at the front-end. It will make our
warnings much smarter.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11492