Hi Jeff,
Thanks as always for the reviews :-)
Jeff Law <l...@redhat.com> writes:
> On 9/11/19 1:03 PM, Richard Sandiford wrote:
>> This patch adds new structures and functions for handling
>> multiple ABIs in a translation unit. The structures are:
>>
>> - predefined_function_abi: describes a static, predefined ABI
>> - function_abi: describes either a predefined ABI or a local
>> variant of one (e.g. taking -fipa-ra into account)
>>
>> The patch adds functions for getting the ABI from a given type
>> or decl; a later patch will also add a function for getting the
>> ABI of the target of a call insn.
>>
>> Although ABIs are about much more than call-clobber/saved choices,
>> I wanted to keep the name general in case we add more ABI-related
>> information in future.
>>
>>
>> 2019-09-11 Richard Sandiford <richard.sandif...@arm.com>
>>
>> gcc/
>> * Makefile.in (OBJS): Add function-abi.o.
>> (GTFILES): Add function-abi.h.
>> * function-abi.cc: New file.
>> * function-abi.h: Likewise.
>> * emit-rtl.h (rtl_data::abi): New field.
>> * function.c: Include function-abi.h.
>> (prepare_function_start): Initialize crtl->abi.
>> * read-rtl-function.c: Include regs.h and function-abi.h.
>> (read_rtl_function_body): Initialize crtl->abi.
>> (read_rtl_function_body_from_file_range): Likewise.
>> * reginfo.c: Include function-abi.h.
>> (init_reg_sets_1): Initialize default_function_abi.
>> (globalize_reg): Call add_full_reg_clobber for each predefined ABI
>> when making a register global.
>> * target-globals.h (this_target_function_abi_info): Declare.
>> (target_globals::function_abi_info): New field.
>> (restore_target_globals): Copy it.
>> * target-globals.c: Include function-abi.h.
>> (default_target_globals): Initialize the function_abi_info field.
>> (target_globals): Allocate it.
>> (save_target_globals): Free it.
> So no problem with this as-is. Questions though:
>
> 1. Do we need to stream this information for LTO?
At the moment this is all derived information rather than something we need
to stream directly. E.g. the set of available predefined_function_abis
really only depends on command-line flags. The mapping from functions
to predefined_function_abis currently depends only on the function type,
so streaming the type is enough to recover the ABI too. function_abi
additionally depends on RTL stuff that doesn't affect LTO.
> 2. Do we need to support it for the RTL front-end, even if primarily for
> testing purposes?
Yeah, I guess it could be useful to be able to pretend that a function
is defined locally with a certain -fipa-ra clobber set, but I think in
most cases it'd be possible to do this using:
void __attribute__ ((noinline, noclone))
callee (void)
{
asm ("" ::: ...regs...);
}
(That's the kind of test I've used in the support for the SVE PCS FWIW,
not posted yet.)
Richard
