[m-dev.] for review: --no-const-ground-terms

[Peter Ross]

Hi,

For Fergus to review, I am not sure if it is trivial to do on the MLDS
backend, so any comments appreciated.


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


Estimated hours taken: 3

Add the option --const-ground-terms, which determines whether or not
static ground terms are output as `const'.  This option will be used to
avoid problem where a static ground term has one of its fields updated
by structure reuse.  This causes a segfault as the memory is readonly.

compiler/llds_out.m:
    Before outputing a `const' check the value of const_ground_terms.

compiler/options.m:
    Add the --const-ground-terms option.

Index: compiler/llds_out.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/llds_out.m,v
retrieving revision 1.157
diff -u -r1.157 llds_out.m
--- compiler/llds_out.m	2000/10/03 00:34:15	1.157
+++ compiler/llds_out.m	2000/10/09 16:12:33
@@ -2090,6 +2090,8 @@
 		globals__io_lookup_bool_option(unboxed_float, UnboxedFloat),
 		globals__io_lookup_bool_option(static_ground_terms,
 			StaticGroundTerms),
+		globals__io_lookup_bool_option(const_ground_terms,
+			ConstGroundTerms),
 		( { UnboxedFloat = no, StaticGroundTerms = yes } ->
 			{ llds_out__float_literal_name(FloatVal, FloatName) },
 			{ FloatLabel = float_label(FloatName) },
@@ -2103,8 +2105,13 @@
 					FloatString) },
 				output_indent(FirstIndent, LaterIndent, N0),
 				{ N is N0 + 1 },
+				{ ConstGroundTerms = yes ->
+					ConstStr = "const"
+				;
+					ConstStr = ""
+				},
 				io__write_strings([
-					"static const MR_Float ",
+					"static ", ConstStr, " MR_Float ",
 					"mercury_float_const_", FloatName,
 					" = ", FloatString, ";\n"
 				])
@@ -2137,6 +2144,8 @@
 	    globals__io_lookup_bool_option(unboxed_float, UnboxFloat),
 	    globals__io_lookup_bool_option(static_ground_terms,
 					StaticGroundTerms),
+	    globals__io_lookup_bool_option(const_ground_terms,
+					ConstGroundTerms),
 	    (
 		{ UnboxFloat = no, StaticGroundTerms = yes },
 		{ llds_out__float_const_binop_expr_name(Op, Rval1, Rval2,
@@ -2150,7 +2159,13 @@
 			{ decl_set_insert(DeclSet2, FloatLabel, DeclSet) },
 			output_indent(FirstIndent, LaterIndent, N2),
 			{ N is N2 + 1 },
-			io__write_string("static const "),
+			{ ConstGroundTerms = yes ->
+				Const = "const "
+			;
+				Const= " "
+			},
+			io__write_string("static "),
+			io__write_string(Const),
 			output_llds_type(float),
 			io__write_string(" mercury_float_const_"),
 			io__write_string(FloatName),
@@ -2292,6 +2307,9 @@
 	% to initialize them dynamically, so we must omit `const'
 	% from the above structure.
 	%
+	% We also omit the `const' if --no-const-ground-terms is
+	% defined.
+	%
 	% Also we now conditionally output some parts.  The parts that
 	% are conditionally output are Def, Decl and Init.  It is an
 	% error for Init to be yes and Decl to be no.
@@ -2324,14 +2342,22 @@
 		),
 		globals__io_get_globals(Globals),
 		{ globals__have_static_code_addresses(Globals, StaticCode) },
+		globals__io_lookup_bool_option(const_ground_terms,
+				ConstGroundTerms),
 		(
 				% Don't make the structure `const'
 				% if the structure will eventually include
 				% code addresses but we don't have static code
-				% addresses.
-			{ StaticCode = no },
-			{ DeclId = data_addr(DataAddr) },
-			{ data_addr_would_include_code_address(DataAddr, yes) }
+				% addresses or --no-const-ground-terms
+				% is defined.
+			(
+				{ StaticCode = no },
+				{ DeclId = data_addr(DataAddr) },
+				{ data_addr_would_include_code_address(
+						DataAddr, yes) }
+			;
+				{ ConstGroundTerms = no }
+			)
 		->
 			[]
 		;
Index: compiler/options.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/options.m,v
retrieving revision 1.293
diff -u -r1.293 options.m
--- compiler/options.m	2000/10/03 00:34:22	1.293
+++ compiler/options.m	2000/10/09 16:12:33
@@ -339,6 +339,7 @@
 		;	  try_switch_size
 		;	  binary_switch_size
 		;	static_ground_terms
+		;	const_ground_terms
 		;	middle_rec
 		;	simple_neg
 		;	follow_vars
@@ -706,6 +707,7 @@
 	try_switch_size		-	int(3),
 	binary_switch_size	-	int(4),
 	static_ground_terms	-	bool(no),
+	const_ground_terms	-	bool(no),
 	middle_rec		-	bool(no),
 	simple_neg		-	bool(no),
 	follow_vars		-	bool(no),
@@ -1086,6 +1088,7 @@
 long_option("try-switch-size",		try_switch_size).
 long_option("binary-switch-size",	binary_switch_size).
 long_option("static-ground-terms",	static_ground_terms).
+long_option("const-ground-terms",	const_ground_terms).
 long_option("middle-rec",		middle_rec).
 long_option("simple-neg",		simple_neg).
 long_option("follow-vars",		follow_vars).
@@ -1346,6 +1349,7 @@
 	optimize_repeat		-	int(1),
 	optimize_peep		-	bool(yes),
 	static_ground_terms	-	bool(yes),
+	const_ground_terms	-	bool(yes),
 	smart_indexing		-	bool(yes),
 	optimize_jumps		-	bool(yes),
 	optimize_labels		-	bool(yes),
@@ -2294,7 +2298,9 @@
 		"\tat compile time and storing them as static constants.",
 		"\tNote that auxiliarity data structures created by the compiler",
 		"\tfor purposes such as debugging will still be created as",
-		"\tstatic constants.",
+		"--no-const-ground-terms",
+		"\tWhen constructing static ground terms don't store them as",
+		"\tconstants.",
 		"--no-middle-rec",
 		"\tDisable the middle recursion optimization.",
 		"--no-simple-neg",

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