On Tue, Jan 03, 2017 at 09:40:02PM +0200, Janne Blomqvist wrote:
> I do think this is fixable without waiting for potential improved
> hardware. The vast majority of uses of boolean_type_node in the
> Fortran frontend is code like
>
> tmp = fold_build2_loc (input_location, GT_EXPR,
> boolean_type_node, from_len,
> build_zero_cst (TREE_TYPE (from_len)));
> tmp = fold_build3_loc (input_location, COND_EXPR,
> void_type_node, tmp, extcopy, stdcopy);
>
> where the result of a boolean expression is returned as a
> boolean_type_node. This is a more like high-level language semantics,
> whereas on the asm level boolean expressions are of course evaluated
> with integer arithmetic (or are there targets where this is not
> true?).
>
> So while the Fortran frontend shouldn't redefine the ABI specified
> boolean_type_node, for situations like the above we could instead use
> some fast_scalar_non_abi_bool_type_node (better name suggestions
> welcome?), if we had some mechanism for returning such information
> from the backend? Or is there some universal best choice here?
>
> Or since boolean types are not actually present at the asm level, what
> is the best choice in cases like the above in order to generate code
> that can be lowered to as efficient code as possible? Should the
> result of the fold_build2_loc be of, say, TREE_TYPE(from_len) instead
> of boolean_type_node (or fast_scalar_non_abi_bool_type_node or
> whatever we come up with)?
>
>
> (Repost without html formatting, sorry for the spam)
Well, generally if it helps Fortran on z10, it will likely help C and C++
too, so you probably instead want some type promotion pass which will know
that on the particular target it is beneficial to promote booleans to
32-bits and know under what circumstances (the loads and stores of course
need to remain the same size for ABI reasons, but as soon as you have it in
SSA_NAME, it depends on what you use it for, sometimes it will be beneficial
to promote it, sometimes not. Of course, that is something that is too late
for GCC 7.
Jakub
