some comments &c

2 files changed, 54 insertions, 14 deletions

diff --git a/main.c b/main.c
index edeb6a5..276ea69 100644
--- a/main.c
+++ b/main.c
@@ -33,6 +33,27 @@ void unit_free(Unit *u) {
 
 Node *parse_expr(Lexer *l, Proc *p);
 
+/* TODO: eliminate unused if-else statements at the end of compilation
+ * they don't get pruned out by peephole optimizations if there are phi
+ * nodes that are connected to keepalive (due to still being in scope).
+ * so probably this will have to be done in a separate step after the
+ * graph has been generated.
+ */
+
+Node *ctrl(Proc *p, Node *n) {
+	if (!n) {
+		p->ctrl = node_new_lit(p, (Value) {
+			.type = { .lvl = T_XCTRL, .t = T_NONE }
+		});
+		return NULL;
+	}
+	if (p->ctrl->val.type.lvl == T_XCTRL) {
+		return NULL;
+	}
+	p->ctrl = n;
+	return n;
+}
+
 void parse_return(Lexer *l, Proc *p) {
 	lex_next(l);
 	Node *n;
@@ -52,9 +73,8 @@ void parse_return(Lexer *l, Proc *p) {
 	if (n->val.type.lvl != T_XCTRL) {
 		node_add(p, n, p->stop);
 	}
-	p->ctrl = node_new_lit(p, (Value) {
-		.type = { .lvl = T_XCTRL, .t = T_NONE }
-	});
+	ctrl(p, n);
+	ctrl(p, NULL);
 }
 
 void parse_let(Lexer *l, Proc *p) {
@@ -131,7 +151,7 @@ void merge_scope(Lexer *l, Proc *p, ScopeNameList *before, ScopeNameList *ntrue,
 			if (yes->node == b4->node && no->node == b4->node) continue;
 			phi = node_new(p, N_PHI, p->ctrl, yes->node, no->node);
 		}
-		fprintf(stderr, "phi('%.*s', %d, %d)\n", (int)b4->name.n, b4->name.s, phi->in.data[1]->id, phi->in.data[2]->id);
+		//fprintf(stderr, "phi('%.*s', %d, %d)\n", (int)b4->name.n, b4->name.s, phi->in.data[1]->id, phi->in.data[2]->id);
 		phi = node_peephole(phi, p, l);
 		NameBinding *b = scope_find(&p->scope, b4->name);
 		assert(b);
@@ -140,6 +160,26 @@ void merge_scope(Lexer *l, Proc *p, ScopeNameList *before, ScopeNameList *ntrue,
 	node_remove(p, p->ctrl, p->keepalive);
 }
 
+/* TODO: find out a way to encode known relations between nodes, based on the
+ * conditional, within the body of an if statement --- e.g., for a statement
+ *
+ * if a < 5 {
+ * 	if a < 10 {
+ * 		foo()
+ * 	}
+ * } else {
+ * 	if a > 3 {
+ * 		bar()
+ * 	}
+ * }
+ *
+ * we should be able to infer that the second condition is always true, because
+ * it's only reachable if a < 5, and 5 < 10.  conversely, in the else branch,
+ * we know that a >= 5, and can use that to make assumptions on comparisons
+ * made there too!
+ *
+ */
+
 void parse_if(Lexer *l, Proc *p) {
 	lex_next(l);
 	Node *cond = parse_expr(l, p);
@@ -170,20 +210,18 @@ void parse_if(Lexer *l, Proc *p) {
 		if (cond->val.i) if_false->val.type.lvl = T_XCTRL;
 		else if_true->val.type.lvl = T_XCTRL;
 	}
-	p->ctrl = if_true;
-	fprintf(stderr, ":+ %d\n", p->ctrl->id);
+	ctrl(p, if_true);
 	//assert(if_true->in.len > 0);
 	lex_expected(l, TM_LBRACE);
 	parse_block(l, p, &scope_true);
 	ctrl_if = p->ctrl;
 	node_add(p, ctrl_if, p->keepalive);
-	fprintf(stderr, ":- %d\n", p->ctrl->id);
 	//assert(ctrl_if->in.len > 0);
 	if (l->tok == TOK_ELSE) {
 		for (int i = 0; i < scope_before.len; i++) {
 			scope_update(scope_find(&p->scope, scope_before.data[i].name), scope_before.data[i].node, p);
 		}
-		p->ctrl = if_false;
+		ctrl(p, if_false);
 		lex_expect(l, TM_LBRACE);
 		parse_block(l, p, &scope_false);
 		ctrl_else = p->ctrl;
@@ -208,7 +246,7 @@ void parse_if(Lexer *l, Proc *p) {
 		assert(if_true->refs > 0);
 		assert(if_false->refs > 0);
 	}
-	p->ctrl = region;
+	ctrl(p, region);
 	node_remove(p, if_true, p->keepalive);
 	node_remove(p, if_false, p->keepalive);
 	//p->ctrl = node_peephole(node_new(p, N_REGION, if_true, if_false), p, l);
@@ -217,12 +255,11 @@ void parse_if(Lexer *l, Proc *p) {
 	scope_uncollect(&p->scope, p, &scope_true);
 	scope_uncollect(&p->scope, p, &scope_false);
 	scope_uncollect(&p->scope, p, &scope_before);
-	fprintf(stderr, "%ld\n", p->ctrl->out.len);
-	node_del_out(p->ctrl, p->keepalive);
+	node_del_out(region, p->keepalive);
 	assert(p->ctrl == region);
 	/* make sure we're not orphaning any phi nodes*/
 	if (p->ctrl->out.len < 1) {
-		p->ctrl = node_peephole(p->ctrl, p, l);
+		ctrl(p, node_peephole(p->ctrl, p, l));
 	}
 }
 
diff --git a/test.lang b/test.lang
index f717086..d7f3c89 100644
--- a/test.lang
+++ b/test.lang
@@ -1,6 +1,9 @@
 func main(a, b i64) i64 {
 	if a < b {
-		return a + b
+		let t = a
+		a := b
+		b := t
 	}
-	return b
+	/* TODO: error on failing to return from a function */
+	return a + b
 }