diff --git a/src/Make.conf b/src/Make.conf
index 3542b70eef..29f352079e 100644
--- a/src/Make.conf
+++ b/src/Make.conf
@@ -4,7 +4,7 @@
 
 CC=quietgcc
 LD=quietgcc
-CFLAGS=-ggdb -I$(GOROOT)/include
+CFLAGS=-ggdb -I$(GOROOT)/include -O1
 BIN=$(HOME)/bin
 O=o
 YFLAGS=-d
diff --git a/src/cmd/6g/obj.c b/src/cmd/6g/obj.c
index 76c6a93e28..85e668d668 100644
--- a/src/cmd/6g/obj.c
+++ b/src/cmd/6g/obj.c
@@ -635,12 +635,14 @@ dumpsigt(Type *progt, Type *ifacet, Type *rcvrt, Type *methodt, Sym *s)
 	Iter savet;
 	Prog *oldlist;
 	Sym *method;
+	uint32 sighash;
 
 	at.sym = s;
 
 	a = nil;
 	o = 0;
 	oldlist = nil;
+	sighash = 0;
 	for(f=methodt->method; f!=T; f=f->down) {
 		if(f->type->etype != TFUNC)
 			continue;
@@ -662,6 +664,8 @@ dumpsigt(Type *progt, Type *ifacet, Type *rcvrt, Type *methodt, Sym *s)
 			a->hash += PRIME10*stringhash(package);
 		a->perm = o;
 		a->sym = methodsym(method, rcvrt);
+		
+		sighash = sighash*100003 + a->hash;
 
 		if(!a->sym->siggen) {
 			a->sym->siggen = 1;
@@ -709,7 +713,7 @@ dumpsigt(Type *progt, Type *ifacet, Type *rcvrt, Type *methodt, Sym *s)
 	ot = 0;
 	ot = rnd(ot, maxround);	// base structure
 
-	// sigi[0].name = ""
+	// sigt[0].name = ""
 	ginsatoa(widthptr, stringo);
 
 	// save type name for runtime error message.
@@ -718,10 +722,10 @@ dumpsigt(Type *progt, Type *ifacet, Type *rcvrt, Type *methodt, Sym *s)
 
 	// first field of an type signature contains
 	// the element parameters and is not a real entry
-	// sigi[0].hash = elemalg
-	gensatac(wi, algtype(progt));
+	// sigt[0].hash = elemalg + sighash<<8
+	gensatac(wi, algtype(progt) + (sighash<<8));
 
-	// sigi[0].offset = width
+	// sigt[0].offset = width
 	gensatac(wi, progt->width);
 
 	// skip the function
@@ -730,10 +734,10 @@ dumpsigt(Type *progt, Type *ifacet, Type *rcvrt, Type *methodt, Sym *s)
 	for(b=a; b!=nil; b=b->link) {
 		ot = rnd(ot, maxround);	// base structure
 
-		// sigx[++].name = "fieldname"
+		// sigt[++].name = "fieldname"
 		ginsatoa(widthptr, stringo);
 
-		// sigx[++].hash = hashcode
+		// sigt[++].hash = hashcode
 		gensatac(wi, b->hash);
 
 		// sigt[++].offset = of embedded struct
@@ -770,11 +774,13 @@ dumpsigi(Type *t, Sym *s)
 	Sig *a, *b;
 	Prog *p;
 	char buf[NSYMB];
+	uint32 sighash;
 
 	at.sym = s;
 
 	a = nil;
 	o = 0;
+	sighash = 0;
 	for(f=t->type; f!=T; f=f->down) {
 		if(f->type->etype != TFUNC)
 			continue;
@@ -797,6 +803,8 @@ dumpsigi(Type *t, Sym *s)
 		a->perm = o;
 		a->sym = methodsym(f->sym, t);
 		a->offset = 0;
+		
+		sighash = sighash*100003 + a->hash;
 
 		o++;
 	}
@@ -815,8 +823,8 @@ dumpsigi(Type *t, Sym *s)
 	// first field of an interface signature
 	// contains the count and is not a real entry
 
-	// sigi[0].hash = 0
-	gensatac(wi, 0);
+	// sigi[0].hash = sighash
+	gensatac(wi, sighash);
 
 	// sigi[0].offset = count
 	o = 0;
diff --git a/src/runtime/iface.c b/src/runtime/iface.c
index 99116806a3..7d312d22cc 100644
--- a/src/runtime/iface.c
+++ b/src/runtime/iface.c
@@ -40,6 +40,7 @@ struct	Itype
 
 static	Iface	niliface;
 static	Itype*	hash[1009];
+static	Lock	ifacelock;
 
 Sigi	sigi·empty[2] =	{ (byte*)"interface { }" };
 
@@ -113,32 +114,48 @@ printiface(Iface i)
 static Itype*
 itype(Sigi *si, Sigt *st, int32 canfail)
 {
+	int32 locked;
 	int32 nt, ni;
 	uint32 ihash, h;
 	byte *sname, *iname;
 	Itype *m;
 
-	h = ((uint32)(uint64)si + (uint32)(uint64)st) % nelem(hash);
-	for(m=hash[h]; m!=nil; m=m->link) {
-		if(m->sigi == si && m->sigt == st) {
-			if(m->bad) {
-				m = nil;
-				if(!canfail) {
-					// this can only happen if the conversion
-					// was already done once using the , ok form
-					// and we have a cached negative result.
-					// the cached result doesn't record which
-					// interface function was missing, so jump
-					// down to the interface check, which will
-					// give a better error.
-					goto throw;
+	// compiler has provided some good hash codes for us.
+	h = 0;
+	if(si)
+		h += si->hash;
+	if(st)
+		h += st->hash >> 8;
+	h %= nelem(hash);
+
+	// look twice - once without lock, once with.
+	// common case will be no lock contention.
+	for(locked=0; locked<2; locked++) {
+		if(locked)
+			lock(&ifacelock);
+		for(m=hash[h]; m!=nil; m=m->link) {
+			if(m->sigi == si && m->sigt == st) {
+				if(m->bad) {
+					m = nil;
+					if(!canfail) {
+						// this can only happen if the conversion
+						// was already done once using the , ok form
+						// and we have a cached negative result.
+						// the cached result doesn't record which
+						// interface function was missing, so jump
+						// down to the interface check, which will
+						// give a better error.
+						goto throw;
+					}
 				}
+				// prints("old itype\n");
+				if(locked)
+					unlock(&ifacelock);
+				return m;
 			}
-			// prints("old itype\n");
-			return m;
 		}
 	}
-
+	
 	ni = si[0].perm;	// first entry has size
 	m = mal(sizeof(*m) + ni*sizeof(m->fun[0]));
 	m->sigi = si;
@@ -180,6 +197,8 @@ throw:
 				m->bad = 1;
 				m->link = hash[h];
 				hash[h] = m;
+				if(locked)
+					unlock(&ifacelock);
 				return nil;
 			}
 			if(ihash == st[nt].hash && strcmp(sname, iname) == 0)
@@ -190,6 +209,8 @@ throw:
 	m->link = hash[h];
 	hash[h] = m;
 	// printf("new itype %p\n", m);
+	if(locked)
+		unlock(&ifacelock);
 	return m;
 }
 
@@ -216,7 +237,7 @@ sys·ifaceT2I(Sigi *si, Sigt *st, ...)
 		prints("\n");
 	}
 
-	alg = st->hash;
+	alg = st->hash & 0xFF;
 	wid = st->offset;
 	if(wid <= sizeof ret->data)
 		algarray[alg].copy(wid, &ret->data, elem);
@@ -272,7 +293,7 @@ sys·ifaceI2T(Sigt *st, Iface i, ...)
 		throw("interface conversion");
 	}
 
-	alg = st->hash;
+	alg = st->hash & 0xFF;
 	wid = st->offset;
 	if(wid <= sizeof i.data)
 		algarray[alg].copy(wid, ret, &i.data);
@@ -297,7 +318,7 @@ sys·ifaceI2T2(Sigt *st, Iface i, ...)
 	int32 alg, wid;
 
 	ret = (byte*)(&i+1);
-	alg = st->hash;
+	alg = st->hash & 0xFF;
 	wid = st->offset;
 	ok = (bool*)(ret+rnd(wid, 8));
 
@@ -411,7 +432,7 @@ ifacehash(Iface a)
 	
 	if(a.type == nil)
 		return 0;
-	alg = a.type->sigt->hash;
+	alg = a.type->sigt->hash & 0xFF;
 	wid = a.type->sigt->offset;
 	if(algarray[alg].hash == nohash) {
 		// calling nohash will throw too,
@@ -450,14 +471,12 @@ ifaceeq(Iface i1, Iface i2)
 	if(i2.type == nil)
 		goto no;
 
-	// value
-	alg = i1.type->sigt->hash;
-	if(alg != i2.type->sigt->hash)
+	// are they the same type?
+	if(i1.type->sigt != i2.type->sigt)
 		goto no;
 
+	alg = i1.type->sigt->hash & 0xFF;
 	wid = i1.type->sigt->offset;
-	if(wid != i2.type->sigt->offset)
-		goto no;
 
 	if(algarray[alg].equal == noequal) {
 		// calling noequal will throw too,
@@ -553,20 +572,53 @@ extern int32 ngotypesigs;
 // for .([]int) instead of .(string) above, then there would be a
 // signature with type string "[]int" in gotypesigs, and unreflect
 // wouldn't call fakesigt.
+
+static	Sigt	*fake[1009];
+static	int32	nfake;
+
 static Sigt*
 fakesigt(string type, bool indir)
 {
-	// TODO(rsc): Cache these by type string.
 	Sigt *sigt;
+	uint32 h;
+	int32 i, locked;
+
+	if(type == nil)
+		type = emptystring;
+
+	h = 0;
+	for(i=0; i<type->len; i++)
+		h = h*37 + type->str[i];
+	h += indir;
+	h %= nelem(fake);
+	
+	for(locked=0; locked<2; locked++) {
+		if(locked)
+			lock(&ifacelock);
+		for(sigt = fake[h]; sigt != nil; sigt = (Sigt*)sigt->fun) {
+			// don't need to compare indir.
+			// same type string but different indir will have
+			// different hashes.
+			if(mcmp(sigt->name, type->str, type->len) == 0)
+			if(sigt->name[type->len] == '\0') {
+				if(locked)
+					unlock(&ifacelock);
+				return sigt;
+			}
+		}
+	}
 
 	sigt = mal(2*sizeof sigt[0]);
 	sigt[0].name = mal(type->len + 1);
 	mcpy(sigt[0].name, type->str, type->len);
-	sigt[0].hash = AMEM;	// alg
+	sigt[0].hash = AFAKE;	// alg
 	if(indir)
 		sigt[0].offset = 2*sizeof(niliface.data);  // big width
 	else
 		sigt[0].offset = 1;  // small width
+	sigt->fun = (void*)fake[h];
+	fake[h] = sigt;
+	unlock(&ifacelock);
 	return sigt;
 }
 
@@ -574,31 +626,40 @@ static int32
 cmpstringchars(string a, uint8 *b)
 {
 	int32 i;
+	byte c1, c2;
 
 	for(i=0;; i++) {
-		if(i == a->len) {
-			if(b[i] == 0)
-				return 0;
+		if(i == a->len)
+			c1 = 0;
+		else
+			c1 = a->str[i];
+		c2 = b[i];
+		if(c1 < c2)
 			return -1;
-		}
-		if(b[i] == 0)
-			return 1;
-		if(a->str[i] != b[i]) {
-			if((uint8)a->str[i] < (uint8)b[i])
-				return -1;
-			return 1;
-		}
+		if(c1 > c2)
+			return +1;
+		if(c1 == 0)
+			return 0;
 	}
 }
 
 static Sigt*
 findtype(string type, bool indir)
 {
-	int32 i;
-
-	for(i=0; i<ngotypesigs; i++)
-		if(cmpstringchars(type, gotypesigs[i]->name) == 0)
-			return gotypesigs[i];
+	int32 i, lo, hi, m;
+	
+	lo = 0;
+	hi = ngotypesigs;
+	while(lo < hi) {
+		m = lo + (hi - lo)/2;
+		i = cmpstringchars(type, gotypesigs[m]->name);
+		if(i == 0)
+			return gotypesigs[m];
+		if(i < 0)
+			hi = m;
+		else
+			lo = m+1;
+	}
 	return fakesigt(type, indir);
 }
 
diff --git a/src/runtime/runtime.c b/src/runtime/runtime.c
index ce9349383c..00e3638ab9 100644
--- a/src/runtime/runtime.c
+++ b/src/runtime/runtime.c
@@ -69,6 +69,24 @@ mcpy(byte *t, byte *f, uint32 n)
 	}
 }
 
+int32
+mcmp(byte *s1, byte *s2, uint32 n)
+{
+	uint32 i;
+	byte c1, c2;
+
+	for(i=0; i<n; i++) {
+		c1 = s1[i];
+		c2 = s2[i];
+		if(c1 < c2)
+			return -1;
+		if(c1 > c2)
+			return +1;
+	}
+	return 0;
+}
+
+
 void
 mmov(byte *t, byte *f, uint32 n)
 {
@@ -368,6 +386,23 @@ noequal(uint32 s, void *a, void *b)
 	return 0;
 }
 
+static void
+noprint(uint32 s, void *a)
+{
+	USED(s);
+	USED(a);
+	throw("print of unprintable type");
+}
+
+static void
+nocopy(uint32 s, void *a, void *b)
+{
+	USED(s);
+	USED(a);
+	USED(b);
+	throw("copy of uncopyable type");
+}
+
 Alg
 algarray[] =
 {
@@ -375,5 +410,6 @@ algarray[] =
 [ANOEQ]	{ nohash, noequal, memprint, memcopy },
 [ASTRING]	{ strhash, strequal, strprint, memcopy },
 [AINTER]		{ interhash, interequal, interprint, memcopy },
+[AFAKE]	{ nohash, noequal, noprint, nocopy },
 };
 
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index 47103e253a..170657d86b 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -230,6 +230,7 @@ enum
 	ANOEQ,
 	ASTRING,
 	AINTER,
+	AFAKE,
 	Amax
 };
 
@@ -269,6 +270,7 @@ void	prints(int8*);
 void	printf(int8*, ...);
 byte*	mchr(byte*, byte, byte*);
 void	mcpy(byte*, byte*, uint32);
+int32	mcmp(byte*, byte*, uint32);
 void	mmov(byte*, byte*, uint32);
 void*	mal(uint32);
 uint32	cmpstring(string, string);
diff --git a/test/cmp1.go b/test/cmp1.go
index 82e932f45e..d1a1c7a0b3 100644
--- a/test/cmp1.go
+++ b/test/cmp1.go
@@ -41,7 +41,7 @@ func main()
 	var ic interface{} = c;
 	var id interface{} = d;
 	var ie interface{} = e;
-
+	
 	// these comparisons are okay because
 	// string compare is okay and the others
 	// are comparisons where the types differ.
@@ -53,6 +53,13 @@ func main()
 	istrue(ic == id);
 	istrue(ie == ie);
 
+	// 6g used to let this go through as true.
+	var g uint64 = 123;
+	var h int64 = 123;
+	var ig interface{} = g;
+	var ih interface{} = h;
+	isfalse(ig == ih);
+
 	// map of interface should use == on interface values,
 	// not memory.
 	// TODO: should m[c], m[d] be valid here?