[m-rev.] diff: fix for dummy_var bug

[Fergus Henderson]

Estimated hours taken: 1
Branches: main

Fix a bug where the MLDS back-end was generating references to `dummy_var',
for calls to builtins such as unsafe_promise_unique and unsafe_type_cast
with dummy types such as `io__state'.  Referencing a dummy variable is OK for
`--low-level-data', but it doesn't work with `--high-level-data' (e.g. for
the .NET back-end), because we'd need different dummy variables for each
different type.  It's better to avoid generating such assignments in the
first place.

compiler/ml_code_gen.m:
	Avoiding generating references to dummy_var for calls to
	unsafe_type_cast.

compiler/ml_call_gen.m:
	Avoiding generating references to dummy_var for calls to other
	builtins, such as unsafe_promise_unique.

Index: ml_call_gen.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/ml_call_gen.m,v
retrieving revision 1.36
diff -u -d -u -r1.36 ml_call_gen.m
--- ml_call_gen.m	27 Jan 2003 09:20:48 -0000	1.36
+++ ml_call_gen.m	13 Feb 2003 19:12:35 -0000
@@ -968,9 +960,22 @@
 		(
 			{ SimpleCode = assign(Lval, SimpleExpr) }
 		->
-			{ Rval = ml_gen_simple_expr(SimpleExpr) },
-			{ MLDS_Statement = ml_gen_assign(Lval, Rval,
-				Context) }
+			( 
+				% we need to avoid generating assignments to
+				% dummy variables introduced for types such
+				% as io__state
+				{ Lval = var(_VarName, VarType) },
+				{ VarType = mercury_type(ProgDataType, _, _) },
+				{ type_util__is_dummy_argument_type(
+					ProgDataType) }
+			->
+				{ MLDS_Statements = [] }
+			;
+				{ Rval = ml_gen_simple_expr(SimpleExpr) },
+				{ MLDS_Statement = ml_gen_assign(Lval, Rval,
+					Context) },
+				{ MLDS_Statements = [MLDS_Statement] }
+			)
 		;
 			{ error("Malformed det builtin predicate") }
 		)
@@ -980,7 +985,8 @@
 			{ SimpleCode = test(SimpleTest) }
 		->
 			{ TestRval = ml_gen_simple_expr(SimpleTest) },
-			ml_gen_set_success(TestRval, Context, MLDS_Statement)
+			ml_gen_set_success(TestRval, Context, MLDS_Statement),
+			{ MLDS_Statements = [MLDS_Statement] }
 		;
 			{ error("Malformed semi builtin predicate") }
 		)
@@ -988,7 +994,6 @@
 		{ CodeModel = model_non },
 		{ error("Nondet builtin predicate") }
 	),
-	{ MLDS_Statements = [MLDS_Statement] },
 	{ MLDS_Decls = [] }.
 
 :- func ml_gen_simple_expr(simple_expr(mlds__lval)) = mlds__rval.
Index: ml_code_gen.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/ml_code_gen.m,v
retrieving revision 1.123
diff -u -d -u -r1.123 ml_code_gen.m
--- ml_code_gen.m	11 Feb 2003 02:14:27 -0000	1.123
+++ ml_code_gen.m	14 Feb 2003 07:42:44 -0000
@@ -2073,11 +2101,15 @@
 			{ ArgLvals = [SrcLval, DestLval] },
 			{ ArgTypes = [SrcType, DestType] }
 		->
-			ml_gen_box_or_unbox_rval(SrcType, DestType,
-				lval(SrcLval), CastRval),
-			{ Assign = ml_gen_assign(DestLval, CastRval,
-				Context) },
-			{ MLDS_Statements = [Assign] },
+			( { type_util__is_dummy_argument_type(DestType) } ->
+				{ MLDS_Statements = [] }
+			;
+				ml_gen_box_or_unbox_rval(SrcType, DestType,
+					lval(SrcLval), CastRval),
+				{ Assign = ml_gen_assign(DestLval, CastRval,
+					Context) },
+				{ MLDS_Statements = [Assign] }
+			),
 			{ MLDS_Decls = [] }
 		;
 			{ error("wrong number of args for unsafe_type_cast") }
-- 
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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