[Bug tree-optimization/45034] [4.3/4.4/4.5/4.6 Regression] "safe" conversion from unsigned to signed char gives broken code

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #9 from joseph at codesourcery dot com  2010-07-27 22:42 -------
Subject: Re:  [4.3/4.4/4.5/4.6 Regression] "safe"
 conversion from unsigned to signed char gives broken code

On Tue, 27 Jul 2010, mikpe at it dot uu dot se wrote:

> Personally I think GCC should treat source-level casts as wrapping, regardless
> of -fstrict-overflow and -fno-wrapv.  Perhaps it intends to, and we're just
> seeing the effects of bugs.

This implementation-defined behavior is already documented in 
implement-c.texi:

    @item
    @cite{The result of, or the signal raised by, converting an integer to a
    signed integer type when the value cannot be represented in an object of
    that type (C90 6.2.1.2, C99 6.3.1.3).}

    For conversion to a type of width @math{N}, the value is reduced
    modulo @math{2^N} to be within range of the type; no signal is raised.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45034