[m-rev.] diff: IL back-end: improve commit handling

[Fergus Henderson]

Estimated hours taken: 1
Branches: main

Improve the efficiency and maintainability of the way we handle
commits for the IL back-end.

compiler/ml_code_gen.m:
	Delete the IL-specific code for commit handling.
	This code belongs in mlds_to_il.m.

compiler/mlds_to_il.m:
	Handle do_commit instructions by just doing the equivalent of
	"throw new mercury::runtime::Commit();".  This is more efficient
	than the old code that we used to generate, which would assign
	the result of the newobj instruction to a variable or environment
	field, only to immediately get it back again.

Workspace: /home/mars/fjh/ws1/mercury
Index: compiler/ml_code_gen.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/ml_code_gen.m,v
retrieving revision 1.93
diff -u -d -r1.93 ml_code_gen.m
--- compiler/ml_code_gen.m	2001/07/12 23:58:38	1.93
+++ compiler/ml_code_gen.m	2001/07/13 10:58:07
@@ -1563,9 +1563,11 @@
 		%	    {
 		%       #endif
 		%		MR_COMMIT_TYPE ref;
+		%
 		%		void success() {
 		%			MR_DO_COMMIT(ref);
 		%		}
+		%
 		%		MR_TRY_COMMIT(ref, {
 		%			<Goal && success()>
 		%			succeeded = FALSE;
@@ -1599,29 +1601,9 @@
 		{ DoCommitStmt = do_commit(lval(CommitRefLval)) },
 		{ DoCommitStatement = 
 			mlds__statement(DoCommitStmt, MLDS_Context) },
-		=(MLDSGenInfo),
-		{ ml_gen_info_get_module_info(MLDSGenInfo, ModuleInfo) },
-		{ module_info_globals(ModuleInfo, Globals) },
-		{ globals__get_target(Globals, Target) },
-		{ Target = il ->
-				% XXX would be a good performance thing
-				% to re-use the same pre-allocated commit
-				% object over and over again, instead of
-				% allocating them each time.
-			NewCommitObject = mlds__statement(
-				atomic(new_object(CommitRefLval, no,
-					mlds__commit_type, no, no, [], [])),
-					MLDS_Context),
-			DoCommitBody = ml_gen_block([], 
-				[NewCommitObject,
-				DoCommitStatement],
-				Context)
-		;
-			DoCommitBody = DoCommitStatement
-		},
 		/* pop nesting level */
 		ml_gen_nondet_label_func(SuccessFuncLabel, Context,
-			DoCommitBody, SuccessFunc),
+			DoCommitStatement, SuccessFunc),
 
 		ml_get_env_ptr(EnvPtrRval),
 		{ SuccessCont = success_cont(SuccessFuncLabelRval,
Index: compiler/mlds_to_il.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/mlds_to_il.m,v
retrieving revision 1.47
diff -u -d -r1.47 mlds_to_il.m
--- compiler/mlds_to_il.m	2001/07/13 10:44:01	1.47
+++ compiler/mlds_to_il.m	2001/07/13 11:10:21
@@ -1258,38 +1258,44 @@
 			br(label_target(Label))
 		]) }.
 
-statement_to_il(statement(do_commit(Ref), Context), Instrs) -->
+statement_to_il(statement(do_commit(_Ref), Context), Instrs) -->
 
 	% For commits, we use exception handling.
 	%
-	% We generate code of the following form:
+	% For a do_commit instruction, we generate code equivalent 
+	% to the following C++/C#/Java code:
+	%
+	%	throw new mercury::runtime::Commit();
+	%
+	% In IL the code looks like this:
 	% 
-	% 	<load exception rval -- should be of a special commit type>
+	%	newobj  instance void
+	%		['mercury']'mercury'.'runtime'.'Commit'::.ctor()
 	% 	throw
-	%
 	% 
 
-	load(Ref, RefLoadInstrs),
+	{ NewObjInstr = newobj_constructor(il_commit_class_name) },
 	{ Instrs = tree__list([
 			context_node(Context),
 			comment_node("do_commit/1"),
-			RefLoadInstrs,
+			instr_node(NewObjInstr),
 			instr_node(throw)
 		]) }.
 
-statement_to_il(statement(try_commit(Ref, GoalToTry, CommitHandlerGoal), 
+statement_to_il(statement(try_commit(_Ref, GoalToTry, CommitHandlerGoal), 
 		Context), Instrs) -->
 
 	% For commits, we use exception handling.
 	%
-	% We generate code of the following form:
+	% For try_commit instructions, we generate IL code
+	% of the following form:
 	%
 	% 	.try {	
-	%		GoalToTry
+	%		<GoalToTry>
 	%		leave label1
 	% 	} catch commit_type {
 	%		pop	// discard the exception object
-	% 		CommitHandlerGoal
+	% 		<CommitHandlerGoal>
 	%		leave label1
 	% 	}
 	% 	label1:
@@ -1301,9 +1307,7 @@
 	statement_to_il(CommitHandlerGoal, HandlerInstrsTree),
 	il_info_make_next_label(DoneLabel),
 
-	{ rval_to_type(lval(Ref), MLDSRefType) },
-	DataRep =^ il_data_rep,
-	{ ClassName = mlds_type_to_ilds_class_name(DataRep, MLDSRefType) },
+	{ ClassName = il_commit_class_name },
 	{ Instrs = tree__list([
 		context_node(Context),
 		comment_node("try_commit/3"),

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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