From 820f42d977817785ff198425292cddd5f6900083 Mon Sep 17 00:00:00 2001
From: Ken Thompson <ken@golang.org>
Date: Sat, 7 Mar 2009 17:33:42 -0800
Subject: [PATCH] binary search for constant case statements.

R=r
OCL=25890
CL=25890
---
 src/cmd/gc/swt.c | 215 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 212 insertions(+), 3 deletions(-)

diff --git a/src/cmd/gc/swt.c b/src/cmd/gc/swt.c
index fb3e4b095bb..5f014e9a9f5 100644
--- a/src/cmd/gc/swt.c
+++ b/src/cmd/gc/swt.c
@@ -11,6 +11,7 @@ enum
 	Sfalse,
 	Stype,
 };
+Node*	binarysw(Node *t, Iter *save, Node *name);
 
 /*
  * walktype
@@ -263,6 +264,7 @@ prepsw(Node *sw, int arg)
 	Iter save;
 	Node *name, *bool, *cas;
 	Node *t, *a;
+//dump("prepsw before", sw->nbody->left);
 
 	cas = N;
 	name = N;
@@ -279,7 +281,7 @@ prepsw(Node *sw, int arg)
 loop:
 	if(t == N) {
 		sw->nbody->left = rev(cas);
-//dump("case", sw->nbody->left);
+//dump("prepsw after", sw->nbody->left);
 		return;
 	}
 
@@ -309,21 +311,29 @@ loop:
 		goto loop;
 	}
 
-	a = nod(OIF, N, N);
-	a->nbody = t->right;				// then goto l
 
 	switch(arg) {
 	default:
 		// not bool const
+		a = binarysw(t, &save, name);
+		if(a != N)
+			break;
+
+		a = nod(OIF, N, N);
 		a->ntest = nod(OEQ, name, t->left);	// if name == val
+		a->nbody = t->right;			// then goto l
 		break;
 
 	case Strue:
+		a = nod(OIF, N, N);
 		a->ntest = t->left;			// if val
+		a->nbody = t->right;			// then goto l
 		break;
 
 	case Sfalse:
+		a = nod(OIF, N, N);
 		a->ntest = nod(ONOT, t->left, N);	// if !val
+		a->nbody = t->right;			// then goto l
 		break;
 	}
 	cas = list(cas, a);
@@ -470,3 +480,202 @@ walkswitch(Node *sw)
 	walkstate(sw->nbody);
 //print("normal done\n");
 }
+
+/*
+ * binary search on cases
+ */
+enum
+{
+	Ncase	= 4,	// needed to binary search
+};
+
+typedef	struct	Case	Case;
+struct	Case
+{
+	Node*	node;		// points at case statement
+	Case*	link;		// linked list to link
+};
+#define	C	((Case*)nil)
+
+int
+iscaseconst(Node *t)
+{
+	if(t == N || t->left == N)
+		return 0;
+	switch(whatis(t->left)) {
+	case Wlitfloat:
+	case Wlitint:
+	case Wlitstr:
+		return 1;
+	}
+	return 0;
+}
+
+int
+countcase(Node *t, Iter save)
+{
+	int n;
+
+	// note that the iter is by value,
+	// so cases are not really consumed
+	for(n=0;; n++) {
+		if(!iscaseconst(t))
+			return n;
+		t = listnext(&save);
+	}
+}
+
+Case*
+csort(Case *l, int(*f)(Case*, Case*))
+{
+	Case *l1, *l2, *le;
+
+	if(l == C || l->link == C)
+		return l;
+
+	l1 = l;
+	l2 = l;
+	for(;;) {
+		l2 = l2->link;
+		if(l2 == C)
+			break;
+		l2 = l2->link;
+		if(l2 == C)
+			break;
+		l1 = l1->link;
+	}
+
+	l2 = l1->link;
+	l1->link = C;
+	l1 = csort(l, f);
+	l2 = csort(l2, f);
+
+	/* set up lead element */
+	if((*f)(l1, l2) < 0) {
+		l = l1;
+		l1 = l1->link;
+	} else {
+		l = l2;
+		l2 = l2->link;
+	}
+	le = l;
+
+	for(;;) {
+		if(l1 == C) {
+			while(l2) {
+				le->link = l2;
+				le = l2;
+				l2 = l2->link;
+			}
+			le->link = C;
+			break;
+		}
+		if(l2 == C) {
+			while(l1) {
+				le->link = l1;
+				le = l1;
+				l1 = l1->link;
+			}
+			break;
+		}
+		if((*f)(l1, l2) < 0) {
+			le->link = l1;
+			le = l1;
+			l1 = l1->link;
+		} else {
+			le->link = l2;
+			le = l2;
+			l2 = l2->link;
+		}
+	}
+	le->link = C;
+	return l;
+}
+
+int
+casecmp(Case *c1, Case *c2)
+{
+	int w;
+
+	w = whatis(c1->node->left);
+	if(w != whatis(c2->node->left))
+		fatal("casecmp1");
+
+	switch(w) {
+	case Wlitfloat:
+		return mpcmpfltflt(c1->node->left->val.u.fval, c2->node->left->val.u.fval);
+	case Wlitint:
+		return mpcmpfixfix(c1->node->left->val.u.xval, c2->node->left->val.u.xval);
+	case Wlitstr:
+		return cmpslit(c1->node->left, c2->node->left);
+	}
+
+	fatal("casecmp2");
+	return 0;
+}
+
+Node*
+constsw(Case *c0, int ncase, Node *name)
+{
+	Node *cas, *a;
+	Case *c;
+	int i, n;
+
+	// small number do sequentially
+	if(ncase < Ncase) {
+		cas = N;
+		for(i=0; i<ncase; i++) {
+			a = nod(OIF, N, N);
+			a->ntest = nod(OEQ, name, c0->node->left);
+			a->nbody = c0->node->right;
+			cas = list(cas, a);
+			c0 = c0->link;
+		}
+		return rev(cas);
+	}
+
+	// find center and recur
+	c = c0;
+	n = ncase>>1;
+	for(i=0; i<n; i++)
+		c = c->link;
+
+	a = nod(OIF, N, N);
+	a->ntest = nod(OLE, name, c->node->left);
+	a->nbody = constsw(c0, n+1, name);	// include center
+	a->nelse = constsw(c->link, ncase-n-1, name);	// exclude center
+	return a;
+}
+
+Node*
+binarysw(Node *t, Iter *save, Node *name)
+{
+	Case *c, *c1;
+	int i, ncase;
+	Node *a;
+
+	ncase = countcase(t, *save);
+	if(ncase < Ncase)
+		return N;
+
+	c = C;
+	for(i=1; i<ncase; i++) {
+		c1 = mal(sizeof(*c1));
+		c1->link = c;
+		c1->node = t;
+		c = c1;
+
+		t = listnext(save);
+	}
+
+	// last one shouldnt consume the iter
+	c1 = mal(sizeof(*c1));
+	c1->link = c;
+	c1->node = t;
+	c = c1;
+
+	c = csort(c, casecmp);
+	a = constsw(c, ncase, name);
+//dump("bin", a);
+	return a;
+}