Hi!

Power ISA 2.07 (Power8) introduces transactional memory feature
but ISA3.1 (Power10) removes it.  It exposes one troublesome
issue as PR102059 shows.  Users define some function with
target pragma cpu=power10 then it calls one function with
attribute always_inline which inherits command line option
cpu=power8 which enables HTM implicitly.  The current isa_flags
check doesn't allow this inlining due to "target specific
option mismatch" and error mesasge is emitted.

Normally, the callee function isn't intended to exploit HTM
feature, but the default flag setting make it look it has.
As Richi raised in the PR, we have fp_expressions flag in
function summary, and allow us to check the function actually
contains any floating point expressions to avoid overkill.
So this patch follows the similar idea but is more target
specific, for this rs6000 port specific requirement on HTM
feature check, we would like to check rs6000 specific HTM
built-in functions and inline assembly, it allows targets
to do their own customized checks and updates.

It introduces two target hooks need_ipa_fn_target_info and
update_ipa_fn_target_info.  The former allows target to do
some previous check and decides to collect target specific
information for this function or not.  For some special case,
it can predict the analysis result and push it early without
any scannings.  The latter allows the analyze_function_body
to pass gimple stmts down just like fp_expressions handlings,
target can do its own tricks.  I put them as one hook initially
with one boolean to indicates whether it's initial time, but
the code looks a bit ugly, to separate them seems to have
better readability.

To make it simple, this patch uses HOST_WIDE_INT to record the
flags just like what we use for isa_flags.  For rs6000's HTM
need, one HOST_WIDE_INT variable is quite enough, but it seems
good to have one auto_vec for scalability as I noticed some
targets have more than one HOST_WIDE_INT flag.  For now, this
target information collection is only for always_inline function,
function ipa_merge_fn_summary_after_inlining deals with target
information merging.

The patch has been bootstrapped and regress-tested on
powerpc64le-linux-gnu Power9.

Is it on the right track?

Any comments are highly appreciated!

BR,
Kewen
------
gcc/ChangeLog:

	PR ipa/102059
	* config/rs6000/rs6000-call.c (rs6000_builtin_mask_set_p): New
	function.
	* config/rs6000/rs6000-internal.h (rs6000_builtin_mask_set_p): New
	declare.
	* config/rs6000/rs6000.c (TARGET_NEED_IPA_FN_TARGET_INFO): New macro.
	(TARGET_UPDATE_IPA_FN_TARGET_INFO): Likewise.
	(rs6000_need_ipa_fn_target_info): New function.
	(rs6000_update_ipa_fn_target_info): Likewise.
	(rs6000_can_inline_p): Adjust for ipa function summary target info.
	* ipa-fnsummary.c (ipa_dump_fn_summary): Adjust for ipa function
	summary target info.
	(analyze_function_body): Adjust for ipa function summary target
	info and call hook rs6000_need_ipa_fn_target_info and
	rs6000_update_ipa_fn_target_info.
	(ipa_merge_fn_summary_after_inlining): Adjust for ipa function
	summary target info.
	(inline_read_section): Likewise.
	(ipa_fn_summary_write): Likewise.
	* ipa-fnsummary.h (ipa_fn_summary::target_info): New member.
	* doc/tm.texi: Regenerate.
	* doc/tm.texi.in (TARGET_UPDATE_IPA_FN_TARGET_INFO): Document new
	hook.
	(TARGET_NEED_IPA_FN_TARGET_INFO): Likewise.
	* target.def (update_ipa_fn_target_info): New hook.
	(need_ipa_fn_target_info): Likewise.
	* targhooks.c (default_need_ipa_fn_target_info): New function.
	(default_update_ipa_fn_target_info): Likewise.
	* targhooks.h (default_update_ipa_fn_target_info): New declare.
	(default_need_ipa_fn_target_info): Likewise.

gcc/testsuite/ChangeLog:

	PR ipa/102059
	* gcc.dg/lto/pr102059_0.c: New test.
	* gcc.dg/lto/pr102059_1.c: New test.
	* gcc.dg/lto/pr102059_2.c: New test.
	* gcc.target/powerpc/pr102059-5.c: New test.
	* gcc.target/powerpc/pr102059-6.c: New test.