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Estimated hours taken: 80 Branches: main Heavily polymorphic code, such as that generated by g12, often builds the same typeinfos and typeclass infos over and over again. We have long had caches that avoid building a new typeinfo or typeclass info if some variable in the current scope already contains the right value, but a program that has many scopes may still build the same typeinfo or typeclass info many times. If that typeinfo or typeclass info is a ground term, the code generators will recognize that fact, and will turn all the constructions of that ground term in different scopes into referencess to the same constant structure. However, in the meantime, the program can be much bigger than necessary. In the motivating test case for this change, a single call to fdic_post is preceded by 133 goals that build the four typeclass infos it needs. The main idea of this diff is to construct constant typeinfos and typeclass infos out of line, in a separate data structure. Polymorphism then binds variables representing typeinfo and typeclass infos to reference to these constant structures. In the motivating example, this allows polymorphism.m to insert just four goals before the call to fdic_post, the minimal possible number: one for each typeclass info that predicate needs. On Leslie's bug344 program, this change speeds up the compiler by a factor of five to eight (reducing compile time from about 80 or 85 seconds to 10 or 15). There is a drawback to this scheme, but it is minor. That drawback is that once a constant structure is entered into our database of constant structures, it cannot (yet) be removed. Even if all the references to a constant structure are eliminated by optimizations, the structure will remain. ------------------------------------------ CHANGES IN THE FRONT END compiler/const_struct.m: A new module to look after our new database of constant structures. Currently, its use is enable only on the LLDS and MLDS C backends. compiler/hlds.m: compiler/notes/compiler_design.html: Add the new module to the HLDS package. compiler/hlds_module.m: Include the constant structure database in the module_info. compiler/hlds_data.m: Add two new cons_ids, which refer to typeinfos and typeclass infos implemented as constant structures. Move the code for calculating the number of extra instance args in base_typeclass_infos here from base_typeclass_info.m, since polymorphism.m now needs it too. We can now also eliminate the duplicate copy of that code in higher_order.m. Make an independent optimization: make the restrict_list_elements function more efficient by avoiding redundant tests. compiler/polymorphism.m: When building typeinfo and typeclass infos, keep track of whether the structure being built is constant. If it is, then put it in the database of constant structures, and replace the code building it with a simple reference to that new entry. Since I now expect most goal sequences inserted before goals to be short, consistent use lists of goals to represent these, since the costs of conversions to and from cord form are unlikely to be paid back by the higher efficiency of cord operations on longer sequences. When we want to get the typeclass info of a superclass out of the typeclass info of a subclass, if the typeclass info of the subclass is known, do the extraction here. We used to do this optimization only in higher_order.m, but doing so here reduces the size of the HLDS between polymorphism.m and higher_order.m, and thus improves compilation time. Reorganize some of the structure of this module to make the above changes possible. In particular, our new approach requires making snapshots of the varsets and vartypes, and later restoring those snapshots if the variables allocated turn out to be unnecessary, due to all of them describing the components of a constant structure. The correctness of such code is much easier to check if the taking and restoring of each snapshot takes places in a single predicate. Remove the code moved to higher_order.m. Add some debugging code for now. If no issues arise in the next few weeks, it can be deleted. compiler/modecheck_unify.m: Treat unifications whose right hand side has a cons_id referring to a constant structure specially. compiler/base_typeclass_info.m: Replace the code that is now in num_extra_instance_args with a call to that predicate. Put the arguments of some predicates in a more logical order. compiler/higher_order.m: When looking up the components of existing typeclass infos, handle cases where those typeclass infos are constant structures. Give some types, fields and variables better names. Avoid a redundant map search. Avoid some redundant tests by providing separate predicates to handle higher order calls and method calls. Move the predicate is_typeclass_info_manipulator here from polymorphism.m, since this is the only module that uses that predicate. ------------------------------------------ CHANGES IN THE LLDS BACKEND: compiler/llds.m: Add a type to map constant structure numbers to rvals together with their LLDS types. Introduce a type to represent rvals together with their LLDS types. compiler/mercury_compile_llds_back_end.m: Before we generate code for the predicates of the module, convert the constant structures to typed LLDS rvals. Create a map mapping each constant structure number to the corresponding typed rvals. compiler/proc_gen.m: Take that map, and put it into the code_info, to allow references to those structures to be translated. Put the arguments of some predicates into a more logical order. compiler/code_info.m: Include a map giving the representation of each constant structure in the code_info. compiler/unify_gen.m: Add the predicates needed to convert the constant structures of a module to LLDS rvals. For now, this code works only on the kinds of constant structures generated by polymorphism.m. Handle unifications whose right hand side is a reference to a constant structure. compiler/global_data.m: compiler/stack_layout.m: Use the new typed_rval type where relevant. ------------------------------------------ CHANGES IN THE MLDS BACKEND: compiler/ml_proc_gen.m: Before we generate code for the predicates of the module, convert the constant structures to typed MLDS rvals. Create a map mapping each constant structure number to the corresponding typed rvals. Factor out some code into a predicate of its own. compiler/ml_gen_info.m: Include a map giving the representation of each constant structure in the ml_gen_info. Also add to the ml_gen_info an indication of what GC system we are generating code for, since the code generator needs to know this often. compiler/ml_unify_gen.m: Add the predicates needed to convert the constant structures of a module to MLDS rvals. For now, this code works only on the kinds of constant structures generated by polymorphism.m. Handle unifications whose right hand side is a reference to a constant structure. Simplify some existing code. ------------------------------------------ MINOR CHANGES: mdbcomp/prim_data.m: Add a predicate that gets both the module name and the base name from a sym_name at the same time. This is used for minor speedups in other code updated in this diff. compiler/dead_proc_elim.m: Scan constant structures for references to entities that need to be kept alive. compiler/term_constr_build.m: compiler/term_traversal.m: Do not build size constraints from references to constant structures. The sizes of constant terms don't change, so they are irrelevant when building constraints for finding argument size changes. ------------------------------------------ TRIVIAL CHANGES TO CONFORM TO OTHER CHANGES: compiler/hlds_out_module.m: Print out the constant structure database if asked. doc/user_guide.tex: Document how to ask for it. compiler/hlds_out_util.m: Print out the new cons_ids. compiler/hlds_out_mode.m: Print out the new cons_ids in insts. Remove a compiler abort, to help debug a problem. Improve the structure of a predicate. compiler/hlds_out_goal.m: Fix some missing newlines. compiler/hlds_code_util.m: Add some utility predicates needed by the modules above. Conform to the changes above. compiler/mlds_to_il.m: Reorder some predicates. Conform to the changes above. compiler/bytecode_gen.m: compiler/ctgc.selector.m: compiler/dependency_graph.m: compiler/erl_unify_gen.m: compiler/export.m: compiler/implementation_defined_literals.m: compiler/inst_check.m: compiler/llds_out_globals.m: compiler/mercury_to_mercury.m: compiler/ml_global_data.m: compiler/ml_switch_gen.m: compiler/ml_type_gen.m: compiler/module_qual.m: compiler/prog_rep.m: compiler/prog_type.m: compiler/prog_util.m: compiler/rbmm.execution_path.m: compiler/switch_gen.m: compiler/switch_util.m: compiler/type_ctor_info.m: compiler/unused_imports.m: compiler/var_locn.m: compiler/xml_documentation.m: Conform to the changes above. ------------------------------------------ OTHER INDEPENDENT CHANGES: compiler/handle_options.m: Add a dump option that is useful for debugging when working on polymorphism.m and constant structures. compiler/equiv_type_hlds.m: Fix an old performance bug: make the code handling try goals keep the old memory cells representing such goals, instead of rebuilding them, if no changes took place inside them. compiler/ml_accurate_gc.m: Move a test earlier, to allow us to avoid more work in the common case. compiler/erl_code_gen.m: compiler/error_util.m: compiler/hhf.m: compiler/inst_util.m: compiler/ml_code_util.m: compiler/ml_util.m: compiler/mlds_to_c.m: compiler/modecheck_call.m: compiler/modecheck_util.m: compiler/post_typecheck.m: compiler/size_prof.m: compiler/stack_opt.m: compiler/stratify.m: compiler/unused_args.m: compiler/post_type_analysis.m: library/erland_rtti_implementation.m: Minor cleanups. ------------------------------------------ CHANGES TO THE TEST SUITE: tests/invalid/any_passed_as_ground.err_exp2: tests/invalid/invalid_default_func_1.err_exp2: tests/invalid/invalid_default_func_3.err_exp2: tests/invalid/try_detism.err_exp2: Add second expected output files for these tests. We need alternate expected outputs because the numbers of some of the typeinfo variables mentioned in error message are different depending on whether or not const structures are enabled.