Get quite a long way towards basic output-register equality constraints (needed

to make special nodes like NOP work properly). Realise that the way I'm dealing
with the instruction selector is all wrong; I need to physically copy chunks of
tree to give to burg (so I can terminate them correctly).

mach/proto/mcg/hop.c

@@ -28,11 +28,10 @@ void hop_add_string_insel(struct hop* hop, const char* string)
 	array_append(&hop->insels, insel);
 }
 
-void hop_add_reg_insel(struct hop* hop, struct ir* ir, int insn_no)
+void hop_add_vreg_insel(struct hop* hop, struct vreg* vreg)
 {
-	struct insel* insel = new_insel(INSEL_REG);
-	insel->u.reg.ir = ir;
-	insel->u.reg.insn_no = insn_no;
+	struct insel* insel = new_insel(INSEL_VREG);
+	insel->u.vreg = vreg;
 	array_append(&hop->insels, insel);
 }
 
@@ -61,7 +60,7 @@ void hop_print(char k, struct hop* hop)
 
 		if (soi)
 		{
-			tracef(k, "%c: %d: ", k, hop->id);
+			tracef(k, "%c: %d from $%d: ", k, hop->id, hop->ir->id);
 			soi = false;
 		}
 
@@ -72,8 +71,8 @@ void hop_print(char k, struct hop* hop)
 				soi = true;
 				break;
 
-			case INSEL_REG:
-				tracef(k, "$%d.%d", insel->u.reg.ir->id, insel->u.reg.insn_no);
+			case INSEL_VREG:
+				tracef(k, "%%%d", insel->u.vreg->id);
 				break;
 
 			case INSEL_STRING:

mach/proto/mcg/hop.h

@@ -4,7 +4,7 @@
 enum insel_type
 {
 	INSEL_STRING,
-	INSEL_REG,
+	INSEL_VREG,
 	INSEL_VALUE,
 	INSEL_EOI
 };
@@ -15,12 +15,7 @@ struct insel
 	union
 	{
 		const char* string;
-		struct
-		{
-			struct ir* ir;
-			int insn_no;
-		}
-		reg;
+		struct vreg* vreg;
 		struct ir* value;
 	}
 	u;
@@ -32,12 +27,13 @@ struct hop
 	int insn_no;
 	struct ir* ir;
 	ARRAYOF(struct insel) insels;
+	struct vreg* output;
 };
 
 extern struct hop* new_hop(int insn_no, struct ir* ir);
 
 extern void hop_add_string_insel(struct hop* hop, const char* string);
-extern void hop_add_reg_insel(struct hop* hop, struct ir* ir, int insn_no);
+extern void hop_add_vreg_insel(struct hop* hop, struct vreg* vreg);
 extern void hop_add_value_insel(struct hop* hop, struct ir* ir);
 extern void hop_add_eoi_insel(struct hop* hop);
 

mach/proto/mcg/ir.h

@@ -23,7 +23,7 @@ struct ir
 	void* state_label; /* used by the iburg instruction selector */
 	int insn_no;       /* the table rule number for this instruction */
 	int goal_no;       /* the semantic type of this instruction; not stmt */
-	ARRAYOF(struct hop) hops; /* only for root IRs */
+	IMAPOF(struct hop) hops; /* only for root IRs; by goal */
 };
 
 extern const char* ir_names[];

mach/proto/mcg/mcg.h

@@ -24,6 +24,7 @@
 #include "ir.h"
 #include "mcgg.h"
 #include "hop.h"
+#include "vreg.h"
 #include "basicblock.h"
 #include "procedure.h"
 

mach/proto/mcg/pass_instructionselection.c

@@ -29,7 +29,9 @@ int burm_calculate_label(struct ir* ir)
 
 static void emit_reg(struct ir* ir, int goal)
 {
-    hop_add_reg_insel(current_hop, ir, goal);
+    struct hop* hop = imap_get(&current_ir->hops, goal);
+
+    hop_add_vreg_insel(current_hop, hop->output);
 }
 
 static void emit_string(const char* data)
@@ -50,23 +52,30 @@ static void emit_value(struct ir* ir)
 	hop_add_value_insel(current_hop, ir);
 }
 
-static void emit_resultreg(void)
-{
-}
-
 static void emit_eoi(void)
 {
 	hop_add_eoi_insel(current_hop);
 }
 
+static void emit_constraint_equals(struct ir* ir, int goal)
+{
+    struct hop* hop;
+    
+    if (!goal)
+        goal = 2;
+    hop = imap_get(&current_ir->hops, goal);
+
+    current_hop->output = hop->output;
+}
+
 static const struct burm_emitter_data emitter_data =
 {
     &emit_string,
     &emit_fragment,
     &emit_reg,
     &emit_value,
-    &emit_resultreg,
-    &emit_eoi
+    &emit_eoi,
+    &emit_constraint_equals
 };
 
 
@@ -83,6 +92,11 @@ static void walk_instructions(struct ir* ir, int goal)
     {
         parent_hop = current_hop;
         current_hop = new_hop(insn_no, ir);
+        if (goal != 1)
+        {
+            current_hop->output = new_vreg();
+            imap_add(&current_ir->hops, goal, current_hop);
+        }
     }
 
     burm_kids(ir, insn_no, children);
@@ -102,7 +116,9 @@ static void walk_instructions(struct ir* ir, int goal)
 
     if (!insndata->is_fragment)
     {
-        if (insndata->emitter)
+        /* This may cause the vregs to be reassigned for this instruction (and
+         * fragments contained within it). */
+
         insndata->emitter(ir, &emitter_data);
 
         hop_print('I', current_hop);

mach/proto/mcg/table

@@ -69,6 +69,7 @@ PATTERNS
 
 	reg = in:REG4
 		with (reg == in)
+		emit "reg %reg"
 		cost 1;
 
 	reg = NOP4(in:reg)

mach/proto/mcg/vreg.c

@@ -0,0 +1,10 @@
+#include "mcg.h"
+
+static int vreg_count = 1;
+
+struct vreg* new_vreg(void)
+{
+	struct vreg* vreg = calloc(1, sizeof *vreg);
+	vreg->id = vreg_count++;
+	return vreg;
+}

mach/proto/mcg/vreg.h

@@ -0,0 +1,12 @@
+#ifndef VREG_H
+#define VREG_H
+
+struct vreg
+{
+	int id;
+};
+
+extern struct vreg* new_vreg(void);
+
+#endif
+

util/mcgg/iburg.c

@@ -954,6 +954,49 @@ static void emitpredicatedefinitions(Rule r)
 	}
 }
 
+static void invalid_equals_constraint(Rule rule)
+{
+	yylineno = rule->lineno;
+	yyerror("left hand side of an equality constraint must be the output register");
+	exit(1);
+}
+
+static void emit_ir_expr(Rule rule, const char* label)
+{
+	if (strcmp(label, rule->lhs->name) == 0)
+		print("node, %P%s_NT", label);
+	else
+	{
+		Tree node;
+		uint32_t path = find_label(rule->pattern, label, 0, &node);
+		Nonterm nt = node->op;
+
+		if (path == PATH_MISSING)
+			label_not_found(rule, label);
+
+		print_path(path);
+		if (nt->kind == NONTERM)
+			print(", %P%s_NT", ((Nonterm)node->op)->name);
+		else
+			print(", 0");
+	}
+}
+
+static void emit_constraint(Rule rule, struct constraint* c)
+{
+	switch (c->type)
+	{
+		case CONSTRAINT_EQUALS:
+			if (strcmp(c->left, rule->lhs->name) != 0)
+				invalid_equals_constraint(rule);
+
+			print("%1data->emit_constraint_equals(");
+			emit_ir_expr(rule, c->right);
+			print(");\n");
+			break;
+	}
+}
+
 /* emitinsndata - emit the code generation data */
 static void emitinsndata(Rule rules)
 {
@@ -964,11 +1007,33 @@ static void emitinsndata(Rule rules)
 	while (r)
 	{
 		struct stringfragment* f = r->code.first;
-		if (f)
+
+		if (!f)
 		{
+			/* This instruction has no code; make sure it's not a fragment. */
+			if (r->lhs->is_fragment)
+			{
+				yylineno = r->lineno;
+				yyerror("rule is a fragment, but doesn't emit anything");
+			}
+		}
+
 		print("/* %R */\n", r);
 		print("static void %Pemitter_%d(NODEPTR_TYPE node, const struct %Pemitter_data* data) {\n", r->ern);
 
+		/* Constraints come first, because they may cause vreg reassignment, which
+		 * we want to happen before the instruction emission. */
+
+		{
+			int i;
+
+			for (i=0; i<r->constraints.count; i++)
+			{
+				struct constraint* c = r->constraints.item[i];
+				emit_constraint(r, c);
+			}
+		}
+
 		while (f)
 		{
 			switch (f->data[0])
@@ -1024,17 +1089,6 @@ static void emitinsndata(Rule rules)
 		}
 
 		print("}\n\n");
-		}
-		else
-		{
-			/* This instruction has no code; make sure it's not a fragment. */
-			if (r->lhs->is_fragment)
-			{
-				yylineno = r->lineno;
-				yyerror("rule is a fragment, but doesn't emit anything");
-			}
-		}
-
 		r = r->link;
 	}
 
@@ -1051,11 +1105,7 @@ static void emitinsndata(Rule rules)
 
 		print("%2\"%R\",\n", r);
 
-		print("%2");
-		if (r->code.first)
-			print("&%Pemitter_%d,\n", r->ern);
-		else
-			print("NULL,\n");
+		print("%2&%Pemitter_%d,\n", r->ern);
 
 		if (r->lhs->allocate)
 			print("%2%d,\n", r->lhs->allocate->number);

util/mcgg/mcgg.h

@@ -12,7 +12,6 @@
 		 ((size) == 0) ? 0 : \
 		  (size-1)))
 
-
 #define STATE_TYPE void*
 typedef struct ir* NODEPTR_TYPE;
 
@@ -30,9 +29,8 @@ struct burm_emitter_data
     void (*emit_fragment)(struct ir* ir, int goal);
     void (*emit_reg)(struct ir* ir, int goal);
     void (*emit_value)(struct ir* ir);
-    void (*emit_resultreg)(void);
     void (*emit_eoi)(void);
-    void (*emit_usereg)(struct ir* ir);
+    void (*emit_constraint_equals)(struct ir* rightir, int rightgoal);
 };
 
 typedef void burm_emitter_t(struct ir* ir, const struct burm_emitter_data* data);