[m-dev.] diff: improve performance of jumpopt.m

[Simon Taylor]

Estimated hours taken: 0.25

compiler/jumpopt.m:
	Avoid constructing a comment for a tailcall
	unless it is actually needed. This change reduces
	the time taken by `mmc -C make_hlds' by about 1%.


Index: jumpopt.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/jumpopt.m,v
retrieving revision 1.55
diff -u -u -r1.55 jumpopt.m
--- jumpopt.m	2000/10/13 04:04:46	1.55
+++ jumpopt.m	2000/10/25 15:08:10
@@ -239,7 +239,6 @@
 		TraceLevel, CheckedNondetTailCallInfo0,
 		CheckedNondetTailCallInfo, Instrs) :-
 	Instr0 = Uinstr0 - Comment0,
-	string__append(Comment0, " (redirected return)", Redirect),
 	(
 		Uinstr0 = call(Proc, label(RetLabel), LiveInfos, Context,
 			GoalPath, CallModel)
@@ -257,7 +256,8 @@
 		->
 			opt_util__filter_out_livevals(Between0, Between1),
 			list__append(Between1, [livevals(Livevals) - "",
-				goto(Proc) - Redirect], NewInstrs),
+				goto(Proc) - redirect_comment(Comment0)],
+				NewInstrs),
 			RemainInstrs = Instrs0,
 			CheckedNondetTailCallInfo1 = CheckedNondetTailCallInfo0
 		;
@@ -269,7 +269,8 @@
 			not set__member(RetLabel, LayoutLabels)
 		->
 			list__append(Between, [livevals(Livevals) - "",
-				goto(Proc) - Redirect], NewInstrs),
+				goto(Proc) - redirect_comment(Comment0)],
+				NewInstrs),
 			RemainInstrs = Instrs0,
 			CheckedNondetTailCallInfo1 = CheckedNondetTailCallInfo0
 		;
@@ -290,7 +291,7 @@
 				assign(curfr, lval(succfr(lval(curfr))))
 					- "setup curfr on return from tailcall",
 				livevals(Livevals) - "",
-				goto(Proc) - Redirect
+				goto(Proc) - redirect_comment(Comment0)
 			],
 			RemainInstrs = Instrs0,
 			CheckedNondetTailCallInfo1 = CheckedNondetTailCallInfo0
@@ -319,7 +320,7 @@
 				assign(curfr, lval(succfr(lval(curfr))))
 					- "setup curfr on return from tailcall",
 				livevals(Livevals) - "",
-				goto(Proc) - Redirect,
+				goto(Proc) - redirect_comment(Comment0),
 				label(NewLabel) - "non tail call",
 				Instr0
 			],
@@ -340,7 +341,7 @@
 				NewInstrs = [call(Proc, label(DestLabel),
 					LiveInfos, Context, GoalPath,
 					CallModel)
-					- Redirect],
+					- redirect_comment(Comment0)],
 				RemainInstrs = Instrs0
 			),
 			CheckedNondetTailCallInfo1 = CheckedNondetTailCallInfo0
@@ -627,6 +628,9 @@
 		TraceLevel, CheckedNondetTailCallInfo1,
 		CheckedNondetTailCallInfo, Instrs9),
 	list__append(NewInstrs, Instrs9, Instrs).
+
+:- func redirect_comment(string) = string.
+redirect_comment(Comment0) = string__append(Comment0, " (redirected return)").
 
 % We avoid generating statements that redefine the value of a location
 % by comparing its old contents for non-equality with zero.
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