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Re: nvptx offloading patches [2/n]

On Sat, Nov 01, 2014 at 12:51:32PM +0100, Bernd Schmidt wrote:
> LTO has a mechanism not to stream out common nodes that are expected to be
> identical on each run. When using LTO to communicate between compilers for
> different targets, the va_list_type_node and related ones must be excluded
> from this.
> Richard B mentioned in a recent mail that the i386 backend uses direct
> comparisons to va_list_type_node. After investigating a bit it seems to me
> that this is not actually a problem: what's being compared is the return
> value of ix86_canonical_va_list_type, which always chooses one of
> va_list_type_node or its ABI variants, so the comparison should hold even
> with this patch.
> Bootstrapped and tested on x86_64-linux, ok?

How can the offloading of functions using va_start/va_end/va_arg work,
until we apply (in GCC 6?) Michael's patches and extend them - make
all those 3 internal functions lowered only after IPA?

I mean, nvptx supposedly contains different va_list type (from quick glance
it uses void *, while e.g. x86_64 uses a struct [1]), and we gimplify it
early, so for GCC 5 the only option is IMHO to refuse to compile (sorry?)
when streaming functions that use the host va_list type.

For GCC 6, presumably if it is lowered late, if the host va_list would be
at least as big as target va_list, we could stick stuff in there, or rewrite
to the target va_list.  Still, if e.g. va_list is embedded in structures, or
used in global vars, we'd need to pad the structures or something.


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