[m-rev.] diff: optimize constant string__append

[Peter Ross]

Hi,


===================================================================


Estimated hours taken: 1
Branches: main

compiler/const_prop.m:
	Do constant propogation for string__append.


Index: compiler/const_prop.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/const_prop.m,v
retrieving revision 1.19
diff -u -r1.19 const_prop.m
--- compiler/const_prop.m	5 Nov 2003 03:17:35 -0000	1.19
+++ compiler/const_prop.m	4 Dec 2003 21:31:16 -0000
@@ -51,7 +51,7 @@
 :- import_module parse_tree__inst.
 :- import_module parse_tree__prog_data.
 
-:- import_module bool, list, int, float, map, require.
+:- import_module bool, list, int, float, map, require, string.
 :- import_module std_util.
 
 %------------------------------------------------------------------------------%
@@ -291,6 +291,20 @@
 	Y = _YVar - bound(_YUniq, [functor(float_const(YVal), [])]),
 	YVal \= 0.0,
 	ZVal = unchecked_quotient(XVal, YVal).
+
+	% This isn't actually a builtin.
+evaluate_builtin_tri("string", Name, _, X, Y, Z, Z, string_const(ZVal)) :-
+	( Name = "++"
+	; Name = "append"
+	),
+	X = _XVar - bound(_XUniq, [functor(string_const(XVal), [])]),
+	Y = _YVar - bound(_YUniq, [functor(string_const(YVal), [])]),
+
+		% We can only do the append if Z is free (this allows
+		% us to ignore the mode number and pick up both the
+		% predicate and function versions of append)
+	Z = _ZVar - free,
+	ZVal = XVal ++ YVal.
 
 %------------------------------------------------------------------------------%
 


-- 
Peter Ross		
Software Engineer                                (Work)   +32 2 757 10 15
Mission Critical                                 (Mobile) +32 485 482 559
--------------------------------------------------------------------------
mercury-reviews mailing list
post:  mercury-reviews at cs.mu.oz.au
administrative address: owner-mercury-reviews at cs.mu.oz.au
unsubscribe: Address: mercury-reviews-request at cs.mu.oz.au Message: unsubscribe
subscribe:   Address: mercury-reviews-request at cs.mu.oz.au Message: subscribe
--------------------------------------------------------------------------