Re: [PATCH] Make attribute functions pure

[Richard Sandiford <rsandifo at redhat dot com>]

Paolo Bonzini <paolo.bonzini@polimi.it> writes:
>> But don't the get_attr_* functions usually call recog_memoized?
>> That certainly isn't a pure function.
>
> IIUC, a pure function can modify the global status as long as a single
> call can always give the same result.

Well, that's not what the documentation says:

    @item pure
    @cindex @code{pure} function attribute
    Many functions have no effects except the return value and their
    return value depends only on the parameters and/or global variables.
    [...]

GCC assumes that pure functions don't modify memory.  And even
though recog_memoized() conceptually depends only on PATTERN (insn),
the implementation really does modify insn.  Saying that it's pure
could lead to some subtle miscompilation later.

Richard