https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96680
--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Sandra Loosemore <san...@gcc.gnu.org>: https://gcc.gnu.org/g:1294b819e1207c0ae76db29a75256f3fafd5f262 commit r15-6895-g1294b819e1207c0ae76db29a75256f3fafd5f262 Author: Sandra Loosemore <sloosem...@baylibre.com> Date: Mon Jan 13 20:18:12 2025 +0000 OpenMP: Re-work and extend context selector resolution This patch reimplements the middle-end support for "declare variant" and extends the resolution mechanism to also handle metadirectives (PR112779). It also adds partial support for dynamic selectors (PR113904) and fixes a selector scoring bug reported as PR114596. I hope this rewrite also improves the engineering aspect of the code, e.g. more comments to explain what it is doing. In most cases, variant constructs can be resolved either in the front end or during gimplification; if the variant with the highest score has a static selector, then only that one is emitted. In the case where it has a dynamic selector, it is resolved into a (possibly nested) if/then/else construct, testing the run-time predicate for each selector sorted by decreasing order of score until a static selector is found. In some cases, notably a variant construct in a "declare simd" function which may or may not expand into a simd clone, it may not be possible to score or sort the variants until later in compilation (the ompdevlow pass). In this case the gimplifier emits a loop containing a switch statement with the variants in arbitrary order and uses the OMP_NEXT_VARIANT tree node as a placeholder to control which variant is tested on each iteration of the loop. It looks something like: switch_var = OMP_NEXT_VARIANT (0, state); loop_label: switch (switch_var) { case 1: if (dynamic_selector_predicate_1) { alternative_1; goto end_label; } else { switch_var = OMP_NEXT_VARIANT (1, state); goto loop_label; } case 2: ... } end_label: Note that when there are no dynamic selectors, the loop is unnecessary and only the switch is emitted. Finally, in the ompdevlow pass, the OMP_NEXT_VARIANT magic cookies are resolved and replaced with constants. When compiling with -O we can expect that the loop and switch will be discarded by subsequent optimizations and replaced with direct jumps between the cases, eventually arriving at code with similar control flow to the early-resolution cases. This approach is somewhat simpler than the one currently used for handling declare variant in that all possible code paths are already included in the output of the gimplifier, so it is not necessary to maintain hidden references or data structures pointing to expansions of not-yet-resolved variant constructs and special logic for passing them through LTO (see PR lto/96680). A possible disadvantage of this expansion strategy is that dead code for unused variants in the switch can remain when compiling without -O. If this turns out to be a critical problem (e.g., an unused case includes calls to functions not available to the linker) perhaps some further processing could be performed by default after ompdevlow to simplify such constructs. In order to make this patch more readable for review purposes, it leaves the existing code for "declare variant" resolution (including the above-mentioned LTO hack) in place, in some cases just ifdef-ing out functions that won't compile due to changed interfaces for dependencies. The next patch in the series will delete all the now-unused code. gcc/ChangeLog PR middle-end/114596 PR middle-end/112779 PR middle-end/113904 * Makefile.in (GTFILES): Move omp-general.h earlier; required because of moving score_wide_int declaration to that file. * cgraph.h (struct cgraph_node): Add has_omp_variant_constructs flag. * cgraphclones.cc (cgraph_node::create_clone): Propagate has_omp_variant_constructs flag. * gimplify.cc (omp_resolved_variant_calls): New. (expand_late_variant_directive): New. (find_supercontext): New. (gimplify_variant_call_expr): New. (gimplify_call_expr): Adjust parameters to make fallback available. Update processing for "declare variant" substitution. (is_gimple_stmt): Add OMP_METADIRECTIVE. (omp_construct_selector_matches): Ifdef out unused function. (omp_get_construct_context): New. (gimplify_omp_dispatch): Replace call to deleted function omp_resolve_declare_variant with equivalent logic. (expand_omp_metadirective): New. (expand_late_variant_directive): New. (gimplify_omp_metadirective): New. (gimplify_expr): Adjust arguments to gimplify_call_expr. Add cases for OMP_METADIRECTIVE, OMP_NEXT_VARIANT, and OMP_TARGET_DEVICE_MATCHES. (gimplify_function_tree): Initialize/clean up omp_resolved_variant_calls. * gimplify.h (omp_construct_selector_matches): Delete declaration. (omp_get_construct_context): Declare. * lto-cgraph.cc (lto_output_node): Write has_omp_variant_constructs. (input_overwrite_node): Read has_omp_variant_constructs. * omp-builtins.def (BUILT_IN_OMP_GET_NUM_DEVICES): New. * omp-expand.cc (expand_omp_taskreg): Propagate has_omp_variant_constructs. (expand_omp_target): Likewise. * omp-general.cc (omp_maybe_offloaded): Add construct_context parameter; use it instead of querying gimplifier state. Add comments. (omp_context_name_list_prop): Do not test lang_GNU_Fortran in offload compiler, just use the string as-is. (expr_uses_parm_decl): New. (omp_check_context_selector): Add metadirective_p parameter. Remove sorry for target_device selector. Add additional checks specific to metadirective or declare variant. (make_omp_metadirective_variant): New. (omp_construct_traits_match): New. (omp_context_selector_matches): Temporarily ifdef out the previous code, and add a new implementation based on the old one with different parameters, some unnecessary loops removed, and code re-indented. (omp_target_device_matches_on_host): New. (resolve_omp_target_device_matches): New. (omp_construct_simd_compare): Support matching of "simdlen" and "aligned" clauses. (omp_context_selector_set_compare): Make static. Adjust call to omp_construct_simd_compare. (score_wide_int): Move declaration to omp-general.h. (omp_selector_is_dynamic): New. (omp_device_num_check): New. (omp_dynamic_cond): New. (omp_context_compute_score): Ifdef out the old version and re-implement with different parameters. (omp_complete_construct_context): New. (omp_resolve_late_declare_variant): Ifdef out. (omp_declare_variant_remove_hook): Likewise. (omp_resolve_declare_variant): Likewise. (sort_variant): New. (omp_get_dynamic_candidates): New. (omp_declare_variant_candidates): New. (omp_metadirective_candidates): New. (omp_early_resolve_metadirective): New. (omp_resolve_variant_construct): New. * omp-general.h (score_wide_int): Moved here from omp-general.cc. (struct omp_variant): New. (make_omp_metadirective_variant): Declare. (omp_construct_traits_to_codes): Delete declaration. (omp_check_context_selector): Adjust parameters. (omp_context_selector_matches): Likewise. (omp_context_selector_set_compare): Delete declaration. (omp_resolve_declare_variant): Likewise. (omp_declare_variant_candidates): Declare. (omp_metadirective_candidates): Declare. (omp_get_dynamic_candidates): Declare. (omp_early_resolve_metadirective): Declare. (omp_resolve_variant_construct): Declare. (omp_dynamic_cond): Declare. * omp-offload.cc (resolve_omp_variant_cookies): New. (execute_omp_device_lower): Call the above function to resolve variant directives. Remove call to omp_resolve_declare_variant. (pass_omp_device_lower::gate): Check has_omp_variant_construct bit. * omp-simd-clone.cc (simd_clone_create): Propagate has_omp_variant_constructs bit. * tree-inline.cc (expand_call_inline): Likewise. (tree_function_versioning): Likewise. gcc/c/ChangeLog PR middle-end/114596 PR middle-end/112779 PR middle-end/113904 * c-parser.cc (c_finish_omp_declare_variant): Update for changes to omp-general.h interfaces. gcc/cp/ChangeLog PR middle-end/114596 PR middle-end/112779 PR middle-end/113904 * decl.cc (omp_declare_variant_finalize_one): Update for changes to omp-general.h interfaces. * parser.cc (cp_finish_omp_declare_variant): Likewise. gcc/fortran/ChangeLog PR middle-end/114596 PR middle-end/112779 PR middle-end/113904 * trans-openmp.cc (gfc_trans_omp_declare_variant): Update for changes to omp-general.h interfaces. gcc/testsuite/ PR middle-end/114596 PR middle-end/112779 PR middle-end/113904 * c-c++-common/gomp/declare-variant-12.c: Adjust expected behavior per PR114596. * c-c++-common/gomp/declare-variant-13.c: Test that this is resolvable after gimplification, not just final resolution. * c-c++-common/gomp/declare-variant-14.c: Tweak testcase to ensure that -O causes dead code to be optimized away. * gfortran.dg/gomp/declare-variant-12.f90: Adjust expected behavior per PR114596. * gfortran.dg/gomp/declare-variant-13.f90: Test that this is resolvable after gimplification, not just final resolution. * gfortran.dg/gomp/declare-variant-14.f90: Tweak testcase to ensure that -O causes dead code to be optimized away. Co-Authored-By: Kwok Cheung Yeung <k...@codesourcery.com> Co-Authored-By: Sandra Loosemore <san...@codesourcery.com> Co-Authored-By: Marcel Vollweiler <mar...@codesourcery.com>
