This is v3 of the patch; previous versions were:
  v2: https://gcc.gnu.org/ml/gcc-patches/2018-07/msg00446.html
  v1: https://gcc.gnu.org/ml/gcc-patches/2018-06/msg01462.html

This patch introduces a class opt_problem, along with wrapper
classes for bool (opt_result) and for pointers (e.g. opt_loop_vec_info
for loop_vec_info).

opt_problem instances are created when an optimization problem
is encountered, but only if dump_enabled_p.  They are manually
propagated up the callstack, and are manually reported at the
"top level" of an optimization if dumping is enabled, to give the user
a concise summary of the problem *after* the failure is reported.
In particular, the location of the problematic statement is
captured and emitted, rather than just the loop's location.

For example:

no-vfa-vect-102.c:24:3: missed: couldn't vectorize loop
no-vfa-vect-102.c:27:7: missed: statement clobbers memory: __asm__ __volatile__("" :  :  : "memory");

Changed in v3:
* This version bootstraps and passes regression testing (on
  x86_64-pc-linux-gnu).
* added selftests, to exercise the opt_problem machinery
* removed the "bool to opt_result" ctor, so that attempts to
  use e.g. return a bool from an opt_result-returning function
  will fail at compile time
* use formatted printing within opt_problem ctor to replace the
  various dump_printf_loc calls
* dropped i18n
* changed the sense of vect_analyze_data_ref_dependence's return
  value (see the ChangeLog)
* add MSG_PRIORITY_REEMITTED, so that -fopt-info can show the
  messages, without them messing up the counts in scan-tree-dump-times
  in DejaGnu tests

gcc/ChangeLog:
	* Makefile.in (OBJS): Add opt-problem.o.
	* dump-context.h: Include "selftest.h.
	(selftest::temp_dump_context): New forward decl.
	(class dump_context): Make friend of class
	selftest::temp_dump_context.
	(dump_context::dump_loc_immediate): New decl.
	(class dump_pretty_printer): Move here from dumpfile.c.
	(class temp_dump_context): Move to namespace selftest.
	(temp_dump_context::temp_dump_context): Add param
	"forcibly_enable_dumping".
	(selftest::verify_dumped_text):
	(ASSERT_DUMPED_TEXT_EQ): Move here from dumpfile.c.
	(selftest::verify_item):
	(ASSERT_IS_TEXT): Move here from dumpfile.c.
	(ASSERT_IS_TREE): Likewise.
	(ASSERT_IS_GIMPLE): Likewise.
	* dumpfile.c (dump_context::dump_loc): Move immediate dumping
	to...
	(dump_context::dump_loc_immediate): ...this new function.
	(class dump_pretty_printer): Move to dump-context.h.
	(dump_switch_p_1): Don't enable MSG_PRIORITY_REEMITTED.
	(opt_info_switch_p_1): Enable MSG_PRIORITY_REEMITTED.
	(temp_dump_context::temp_dump_context): Move to "selftest"
	namespace.  Add param "forcibly_enable_dumping", and use it to
	conditionalize the use of m_pp;
	(selftest::verify_dumped_text): Make non-static.
	(ASSERT_DUMPED_TEXT_EQ): Move to dump-context.h.
	(selftest::verify_item): Make non-static.
	(ASSERT_IS_TEXT): Move to dump-context.h.
	(ASSERT_IS_TREE): Likewise.
	(ASSERT_IS_GIMPLE): Likewise.
	(selftest::test_capture_of_dump_calls): Pass "true" for new
	param of temp_dump_context.
	* dumpfile.h (enum dump_flag): Add MSG_PRIORITY_REEMITTED, adding
	it to MSG_ALL_PRIORITIES.  Update values of TDF_COMPARE_DEBUG and
	TDF_COMPARE_DEBUG.
	* opt-problem.cc: New file.
	* opt-problem.h: New file.
	* optinfo-emit-json.cc
	(selftest::test_building_json_from_dump_calls): Pass "true" for
	new param of temp_dump_context.
	* optinfo.cc (optinfo_kind_to_dump_flag): New function.
	(optinfo::emit_for_opt_problem): New function.
	(optinfo::emit): Clarity which emit_item is used.
	* optinfo.h (optinfo::get_dump_location): New accessor.
	(optinfo::emit_for_opt_problem): New decl.
	(optinfo::emit): Make const.
	* selftest-run-tests.c (selftest::run_tests): Call
	selftest::opt_problem_cc_tests.
	* selftest.h (selftest::opt_problem_cc_tests): New decl.
	* tree-data-ref.c (dr_analyze_innermost): Convert return type from
	bool to opt_result, converting fprintf messages to
	opt_result::failure_at calls.  Add "stmt" param for use by the
	failure_at calls.
	(create_data_ref): Pass "stmt" to the dr_analyze_innermost call.
	(runtime_alias_check_p): Convert return type from bool to
	opt_result, converting dump_printf calls to
	opt_result::failure_at, using the statement DDR_A for their
	location.
	(find_data_references_in_stmt): Convert return type from bool to
	opt_result, converting "return false" to opt_result::failure_at
	with a new message.
	* tree-data-ref.h: Include "opt-problem.h".
	(dr_analyze_innermost): Convert return type from bool to opt_result,
	and add a const gimple * param.
	(find_data_references_in_stmt): Convert return type from bool to
	opt_result.
	(runtime_alias_check_p): Likewise.
	* tree-predcom.c (find_looparound_phi): Pass "init_stmt" to
	dr_analyze_innermost.
	* tree-vect-data-refs.c (vect_mark_for_runtime_alias_test):
	Convert return type from bool to opt_result, adding a message for
	the PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS zero case.
	(vect_analyze_data_ref_dependence): Convert return type from bool
	to opt_result.  Change sense of return type from "false"
	effectively meaning "no problems" to "false" meaning a problem,
	so that "return false" becomes "return opt_result::success".
	Convert "return true" calls to opt_result::failure_at, using
	the location of statement A rather than vect_location.
	(vect_analyze_data_ref_dependences): Convert return type from bool
	to opt_result.
	(verify_data_ref_alignment): Likewise, converting dump_printf_loc
	calls to opt_result::failure_at, using the stmt location rather
	than vect_location.
	(vect_verify_datarefs_alignment): Convert return type from bool
	to opt_result.
	(vect_enhance_data_refs_alignment): Likewise.  Split local "stat"
	into multiple more-tightly-scoped copies.
	(vect_analyze_data_refs_alignment): Convert return type from bool
	to opt_result.
	(vect_analyze_data_ref_accesses): Likewise, converting a
	"return false" to a "return opt_result::failure_at", adding a
	new message.
	(vect_prune_runtime_alias_test_list): Convert return type from
	bool to opt_result, converting dump_printf_loc to
	opt_result::failure_at.  Add a %G to show the pertinent statement,
	and use the stmt's location rather than vect_location.
	(vect_find_stmt_data_reference): Convert return type from
	bool to opt_result, converting dump_printf_loc to
	opt_result::failure_at, using stmt's location.
	(vect_analyze_data_refs):  Convert return type from bool to
	opt_result.  Convert "return false" to "return
	opt_result::failure_at", adding messages as needed.
	* tree-vect-loop.c (vect_determine_vf_for_stmt_1): Convert return
	type from bool to opt_result.
	(vect_determine_vf_for_stmt): Likewise.
	(vect_determine_vectorization_factor): Likewise, converting
	dump_printf_loc to opt_result::failure_at, using location of phi
	rather than vect_location.
	(vect_analyze_loop_form_1): Convert return type from bool to
	opt_result, converting dump_printf_loc calls, retaining the use of
	vect_location.
	(vect_analyze_loop_form): Convert return type from loop_vec_info
	to opt_loop_vec_info.
	(vect_analyze_loop_operations): Convert return type from bool to
	opt_result, converting dump_printf_loc calls, using the location
	of phi/stmt rather than vect_location where available.  Convert
	various "return false" to "return opt_result::failure_at" with
	"unsupported phi" messages.
	(vect_get_datarefs_in_loop): Convert return type from bool to
	opt_result.  Add a message for the
	PARAM_LOOP_MAX_DATAREFS_FOR_DATADEPS failure.
	(vect_analyze_loop_2): Convert return type from bool to
	opt_result.  Ensure "ok" is set to a opt_result::failure_at before
	each "goto again;", adding new messages where needed.
	Add "unsupported grouped {store|load}" messages.
	(vect_analyze_loop): Convert return type from loop_vec_info to
	opt_loop_vec_info.
	* tree-vect-slp.c (vect_analyze_slp): Convert return type from
	bool to opt_result.
	* tree-vect-stmts.c (process_use): Likewise, converting
	dump_printf_loc call and using stmt location, rather than
	vect_location.
	(vect_mark_stmts_to_be_vectorized): Likeise.
	(vect_analyze_stmt): Likewise, adding a %G.
	(vect_get_vector_types_for_stmt): Convert return type from bool to
	opt_result, converting dump_printf_loc calls and using stmt
	location, rather than vect_location.
	(vect_get_mask_type_for_stmt): Convert return type from tree to
	opt_tree, converting dump_printf_loc calls and using stmt location.
	* tree-vectorizer.c: Include "opt-problem.h.
	(try_vectorize_loop_1): Flag "Analyzing loop at" dump message as
	MSG_PRIORITY_INTERNALS.  Convert local "loop_vinfo" from
	loop_vec_info to opt_loop_vec_info.  If if fails, and dumping is
	enabled, use it to report at the top level "couldn't vectorize
	loop" followed by the problem.
	* tree-vectorizer.h (opt_loop_vec_info): New typedef.
	(vect_mark_stmts_to_be_vectorized): Convert return type from bool
	to opt_result.
	(vect_analyze_stmt): Likewise.
	(vect_get_vector_types_for_stmt): Likewise.
	(tree vect_get_mask_type_for_stmt): Likewise.
	(vect_analyze_data_ref_dependences): Likewise.
	(vect_enhance_data_refs_alignment): Likewise.
	(vect_analyze_data_refs_alignment): Likewise.
	(vect_verify_datarefs_alignment): Likewise.
	(vect_analyze_data_ref_accesses): Likewise.
	(vect_prune_runtime_alias_test_list): Likewise.
	(vect_find_stmt_data_reference): Likewise.
	(vect_analyze_data_refs): Likewise.
	(vect_analyze_loop): Convert return type from loop_vec_info to
	opt_loop_vec_info.
	(vect_analyze_loop_form): Likewise.
	(vect_analyze_slp): Convert return type from bool to opt_result.

gcc/testsuite/ChangeLog:
	* gcc.dg/vect/nodump-vect-opt-info-2.c: New test.
	* gcc.dg/vect/vect-alias-check-4.c: Add "-fopt-info-vec-all" to
	dg-additional-options.  Add dg-message and dg-missed directives
	to verify that -fopt-info messages are written at the correct
	locations.

From-SVN: r264852