v8:
 1. Rebase to master with Martin's static function (r280043) comments merge.
    Boostrap/testsuite/SPEC2017 tested pass on Power8-LE.
 2. TODO:
    2.1. C++ devirt for multiple speculative call targets.
    2.2. ipa-icf ipa_merge_profiles refine with COMDAT inline testcase.

This patch aims to fix PR69678 caused by PGO indirect call profiling
performance issues.
The bug that profiling data is never working was fixed by Martin's pull
back of topN patches, performance got GEOMEAN ~1% improvement(+24% for
511.povray_r specifically).
Still, currently the default profile only generates SINGLE indirect target
that called more than 75%.  This patch leverages MULTIPLE indirect
targets use in LTO-WPA and LTO-LTRANS stage, as a result, function
specialization, profiling, partial devirtualization, inlining and
cloning could be done successfully based on it.
Performance can get improved from 0.70 sec to 0.38 sec on simple tests.
Details are:
  1.  PGO with topn is enabled by default now, but only one indirect
  target edge will be generated in ipa-profile pass, so add variables to enable
  multiple speculative edges through passes, speculative_id will record the
  direct edge index bind to the indirect edge, indirect_call_targets length
  records how many direct edges owned by the indirect edge, postpone gimple_ic
  to ipa-profile like default as inline pass will decide whether it is benefit
  to transform indirect call.
  2.  Use speculative_id to track and search the reference node matched
  with the direct edge's callee for multiple targets.  Actually, it is the
  caller's responsibility to handle the direct edges mapped to same indirect
  edge.  speculative_call_info will return one of the direct edge specified,
  this will leverage current IPA edge process framework mostly.
  3.  Enable LTO WPA/LTRANS stage multiple indirect call targets analysis for
  profile full support in ipa passes and cgraph_edge functions.  speculative_id
  can be set by make_speculative id when multiple targets are binded to
  one indirect edge, and cloned if new edge is cloned.  speculative_id
  is streamed out and stream int by lto like lto_stmt_uid.
  4.  Create and duplicate all speculative direct edge's call summary
  in ipa-fnsummary.c with auto_vec.
  5.  Add 1 in module testcase and 2 cross module testcases.
  6.  Bootstrap and regression test passed on Power8-LE.  No function
  and performance regression for SPEC2017.

gcc/ChangeLog

	2020-01-14  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	PR ipa/69678
	* cgraph.c (symbol_table::create_edge): Init speculative_id and
	target_prob.
	(cgraph_edge::make_speculative): Add param for setting speculative_id
	and target_prob.
	(cgraph_edge::speculative_call_info): Update comments and find reference
	by speculative_id for multiple indirect targets.
	(cgraph_edge::resolve_speculation): Decrease the speculations
	for indirect edge, drop it's speculative if not direct target
	left. Update comments.
	(cgraph_edge::redirect_call_stmt_to_callee): Likewise.
	(cgraph_node::dump): Print num_speculative_call_targets.
	(cgraph_node::verify_node): Don't report error if speculative
	edge not include statement.
	(cgraph_edge::num_speculative_call_targets_p): New function.
	* cgraph.h (int common_target_id): Remove.
	(int common_target_probability): Remove.
	(num_speculative_call_targets): New variable.
	(make_speculative): Add param for setting speculative_id.
	(cgraph_edge::num_speculative_call_targets_p): New declare.
	(target_prob): New variable.
	(speculative_id): New variable.
	* ipa-fnsummary.c (analyze_function_body): Create and duplicate
	  call summaries for multiple speculative call targets.
	* cgraphclones.c (cgraph_node::create_clone): Clone speculative_id.
	* ipa-profile.c (struct speculative_call_target): New struct.
	(class speculative_call_summary): New class.
	(class speculative_call_summaries): New class.
	(call_sums): New variable.
	(ipa_profile_generate_summary): Generate indirect multiple targets summaries.
	(ipa_profile_write_edge_summary): New function.
	(ipa_profile_write_summary): Stream out indirect multiple targets summaries.
	(ipa_profile_dump_all_summaries): New function.
	(ipa_profile_read_edge_summary): New function.
	(ipa_profile_read_summary_section): New function.
	(ipa_profile_read_summary): Stream in indirect multiple targets summaries.
	(ipa_profile): Generate num_speculative_call_targets from
	profile summaries.
	* ipa-ref.h (speculative_id): New variable.
	* ipa-utils.c (ipa_merge_profiles): Update with target_prob.
	* lto-cgraph.c (lto_output_edge): Remove indirect common_target_id and
	common_target_probability.   Stream out speculative_id and
	num_speculative_call_targets.
	(input_edge): Likewise.
	* predict.c (dump_prediction): Remove edges count assert to be
	precise.
	* symtab.c (symtab_node::create_reference): Init speculative_id.
	(symtab_node::clone_references): Clone speculative_id.
	(symtab_node::clone_referring): Clone speculative_id.
	(symtab_node::clone_reference): Clone speculative_id.
	(symtab_node::clear_stmts_in_references): Clear speculative_id.
	* tree-inline.c (copy_bb): Duplicate all the speculative edges
	if indirect call contains multiple speculative targets.
	* value-prof.h  (check_ic_target): Remove.
	* value-prof.c  (gimple_value_profile_transformations):
	Use void function gimple_ic_transform.
	* value-prof.c  (gimple_ic_transform): Handle topn case.
	Fix comment typos.  Change it to a void function.

gcc/testsuite/ChangeLog

	2020-01-14  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	PR ipa/69678
	* gcc.dg/tree-prof/indir-call-prof-topn.c: New testcase.
	* gcc.dg/tree-prof/crossmodule-indir-call-topn-1.c: New testcase.
	* gcc.dg/tree-prof/crossmodule-indir-call-topn-1a.c: New testcase.
	* gcc.dg/tree-prof/crossmodule-indir-call-topn-2.c: New testcase.
	* lib/scandump.exp: Dump executable file name.
	* lib/scanwpaipa.exp: New scan-pgo-wap-ipa-dump.