[m-rev.] for review: speedup some dependency computation in mmc --make

[Peter Wang]

(!)

Branches: main

Fix pathological (?) behaviour in the computation of dependencies
by `mmc --make'.

In one workspace, `mmc --make' now takes 2 seconds to check that all the .c
files in the compiler directory are up to date.  Previously, it took 132
seconds.

compiler/make.dependencies.m:
	In find_transitive_implementation_imports, accumulate dependencies
	starting from a singleton set, instead of accumulating from an empty
	set and adding that single element afterwards.

Index: compiler/make.dependencies.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/make.dependencies.m,v
retrieving revision 1.47
diff -u -p -r1.47 make.dependencies.m
--- compiler/make.dependencies.m	27 Mar 2008 02:29:41 -0000	1.47
+++ compiler/make.dependencies.m	25 Jun 2008 02:33:21 -0000
@@ -823,7 +823,7 @@ init_cached_transitive_dependencies = ma
 
 find_reachable_local_modules(ModuleName, Success, Modules, !Info, !IO) :-
     find_transitive_module_dependencies(all_dependencies, local_module,
-        ModuleName, Success, Modules, !Info, !IO).
+        ModuleName, Success, set.init, Modules, !Info, !IO).
 
 :- pred find_transitive_implementation_imports(module_name::in, bool::out,
     set(module_name)::out, make_info::in, make_info::out,
@@ -831,9 +831,9 @@ find_reachable_local_modules(ModuleName,
 
 find_transitive_implementation_imports(ModuleName, Success, Modules,
         !Info, !IO) :-
+    Modules0 = set.make_singleton_set(ModuleName),
     find_transitive_module_dependencies(all_imports, any_module,
-        ModuleName, Success, Modules0, !Info, !IO),
-    Modules = set.insert(Modules0, ModuleName).
+        ModuleName, Success, Modules0, Modules, !Info, !IO).
 
 :- pred find_transitive_interface_imports(module_name::in, bool::out,
     set(module_name)::out, make_info::in, make_info::out,
@@ -841,19 +841,20 @@ find_transitive_implementation_imports(M
 
 find_transitive_interface_imports(ModuleName, Success, Modules, !Info, !IO) :-
     find_transitive_module_dependencies(interface_imports, any_module,
-        ModuleName, Success, Modules0, !Info, !IO),
+        ModuleName, Success, set.init, Modules0, !Info, !IO),
     set.delete(Modules0, ModuleName, Modules).
 
 :- pred find_transitive_module_dependencies(transitive_dependencies_type::in,
-    module_locn::in, module_name::in, bool::out, set(module_name)::out,
-    make_info::in, make_info::out, io::di, io::uo) is det.
+    module_locn::in, module_name::in, bool::out, set(module_name)::in,
+    set(module_name)::out, make_info::in, make_info::out, io::di, io::uo)
+    is det.
 
 find_transitive_module_dependencies(DependenciesType, ModuleLocn,
-        ModuleName, Success, Modules, !Info, !IO) :-
+        ModuleName, Success, Modules0, Modules, !Info, !IO) :-
     globals.io_lookup_bool_option(keep_going, KeepGoing, !IO),
     find_transitive_module_dependencies_2(KeepGoing,
         DependenciesType, ModuleLocn, ModuleName,
-        Success, set.init, Modules, !Info, !IO),
+        Success, Modules0, Modules, !Info, !IO),
     DepsRoot = transitive_dependencies_root(ModuleName, DependenciesType,
         ModuleLocn),
     !:Info = !.Info ^ cached_transitive_dependencies ^ elem(DepsRoot)


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