[Bug middle-end/11492] Unsigned char promoted to signed int in for loop test for gpp but not gcc

[manu 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