diff --git a/src/cmd/5g/opt.h b/src/cmd/5g/opt.h
index 15b9d14582..e3e3f78ed2 100644
--- a/src/cmd/5g/opt.h
+++ b/src/cmd/5g/opt.h
@@ -96,6 +96,7 @@ EXTERN	Bits	externs;
 EXTERN	Bits	params;
 EXTERN	Bits	consts;
 EXTERN	Bits	addrs;
+EXTERN	Bits	ivar;
 EXTERN	Bits	ovar;
 EXTERN	int	change;
 EXTERN	int32	maxnr;
diff --git a/src/cmd/5g/reg.c b/src/cmd/5g/reg.c
index 80a14db3c4..3eadde4cf4 100644
--- a/src/cmd/5g/reg.c
+++ b/src/cmd/5g/reg.c
@@ -57,7 +57,7 @@ rcmp(const void *a1, const void *a2)
 }
 
 static void
-setoutvar(void)
+setvar(Bits *dst, Type **args)
 {
 	Type *t;
 	Node *n;
@@ -66,18 +66,16 @@ setoutvar(void)
 	Bits bit;
 	int z;
 
-	t = structfirst(&save, getoutarg(curfn->type));
+	t = structfirst(&save, args);
 	while(t != T) {
 		n = nodarg(t, 1);
 		a = zprog.from;
 		naddr(n, &a, 0);
 		bit = mkvar(R, &a);
 		for(z=0; z<BITS; z++)
-			ovar.b[z] |= bit.b[z];
+			dst->b[z] |= bit.b[z];
 		t = structnext(&save);
 	}
-//if(bany(&ovar))
-//print("ovar = %Q\n", ovar);
 }
 
 void
@@ -190,11 +188,14 @@ regopt(Prog *firstp)
 		params.b[z] = 0;
 		consts.b[z] = 0;
 		addrs.b[z] = 0;
+		ivar.b[z] = 0;
 		ovar.b[z] = 0;
 	}
 
-	// build list of return variables
-	setoutvar();
+	// build lists of parameters and results
+	setvar(&ivar, getthis(curfn->type));
+	setvar(&ivar, getinarg(curfn->type));
+	setvar(&ovar, getoutarg(curfn->type));
 
 	/*
 	 * pass 1
@@ -895,8 +896,12 @@ prop(Reg *r, Bits ref, Bits cal)
 		case ABL:
 			if(noreturn(r1->f.prog))
 				break;
+
+			// Mark all input variables (ivar) as used, because that's what the
+			// liveness bitmaps say. The liveness bitmaps say that so that a
+			// panic will not show stale values in the parameter dump.
 			for(z=0; z<BITS; z++) {
-				cal.b[z] |= ref.b[z] | externs.b[z];
+				cal.b[z] |= ref.b[z] | externs.b[z] | ivar.b[z];
 				ref.b[z] = 0;
 			}
 			
diff --git a/src/cmd/6g/opt.h b/src/cmd/6g/opt.h
index 3dcc3d7476..bf356af0c6 100644
--- a/src/cmd/6g/opt.h
+++ b/src/cmd/6g/opt.h
@@ -94,6 +94,7 @@ EXTERN	Bits	externs;
 EXTERN	Bits	params;
 EXTERN	Bits	consts;
 EXTERN	Bits	addrs;
+EXTERN	Bits	ivar;
 EXTERN	Bits	ovar;
 EXTERN	int	change;
 EXTERN	int32	maxnr;
diff --git a/src/cmd/6g/reg.c b/src/cmd/6g/reg.c
index 484c1c0cde..a1f0c756aa 100644
--- a/src/cmd/6g/reg.c
+++ b/src/cmd/6g/reg.c
@@ -55,7 +55,7 @@ rcmp(const void *a1, const void *a2)
 }
 
 static void
-setoutvar(void)
+setvar(Bits *dst, Type **args)
 {
 	Type *t;
 	Node *n;
@@ -64,18 +64,16 @@ setoutvar(void)
 	Bits bit;
 	int z;
 
-	t = structfirst(&save, getoutarg(curfn->type));
+	t = structfirst(&save, args);
 	while(t != T) {
 		n = nodarg(t, 1);
 		a = zprog.from;
 		naddr(n, &a, 0);
 		bit = mkvar(R, &a);
 		for(z=0; z<BITS; z++)
-			ovar.b[z] |= bit.b[z];
+			dst->b[z] |= bit.b[z];
 		t = structnext(&save);
 	}
-//if(bany(&ovar))
-//print("ovars = %Q\n", ovar);
 }
 
 static void
@@ -176,11 +174,14 @@ regopt(Prog *firstp)
 		params.b[z] = 0;
 		consts.b[z] = 0;
 		addrs.b[z] = 0;
+		ivar.b[z] = 0;
 		ovar.b[z] = 0;
 	}
 
-	// build list of return variables
-	setoutvar();
+	// build lists of parameters and results
+	setvar(&ivar, getthis(curfn->type));
+	setvar(&ivar, getinarg(curfn->type));
+	setvar(&ovar, getoutarg(curfn->type));
 
 	/*
 	 * pass 1
@@ -750,8 +751,12 @@ prop(Reg *r, Bits ref, Bits cal)
 		case ACALL:
 			if(noreturn(r1->f.prog))
 				break;
+
+			// Mark all input variables (ivar) as used, because that's what the
+			// liveness bitmaps say. The liveness bitmaps say that so that a
+			// panic will not show stale values in the parameter dump.
 			for(z=0; z<BITS; z++) {
-				cal.b[z] |= ref.b[z] | externs.b[z];
+				cal.b[z] |= ref.b[z] | externs.b[z] | ivar.b[z];
 				ref.b[z] = 0;
 			}
 			
diff --git a/src/cmd/8g/opt.h b/src/cmd/8g/opt.h
index b8f1875d80..77a69e13ab 100644
--- a/src/cmd/8g/opt.h
+++ b/src/cmd/8g/opt.h
@@ -109,6 +109,7 @@ EXTERN	Bits	externs;
 EXTERN	Bits	params;
 EXTERN	Bits	consts;
 EXTERN	Bits	addrs;
+EXTERN	Bits	ivar;
 EXTERN	Bits	ovar;
 EXTERN	int	change;
 EXTERN	int32	maxnr;
diff --git a/src/cmd/8g/reg.c b/src/cmd/8g/reg.c
index d17e18b227..046011c905 100644
--- a/src/cmd/8g/reg.c
+++ b/src/cmd/8g/reg.c
@@ -55,7 +55,7 @@ rcmp(const void *a1, const void *a2)
 }
 
 static void
-setoutvar(void)
+setvar(Bits *dst, Type **args)
 {
 	Type *t;
 	Node *n;
@@ -64,18 +64,16 @@ setoutvar(void)
 	Bits bit;
 	int z;
 
-	t = structfirst(&save, getoutarg(curfn->type));
+	t = structfirst(&save, args);
 	while(t != T) {
 		n = nodarg(t, 1);
 		a = zprog.from;
 		naddr(n, &a, 0);
 		bit = mkvar(R, &a);
 		for(z=0; z<BITS; z++)
-			ovar.b[z] |= bit.b[z];
+			dst->b[z] |= bit.b[z];
 		t = structnext(&save);
 	}
-//if(bany(ovar))
-//print("ovars = %Q\n", ovar);
 }
 
 static void
@@ -146,11 +144,14 @@ regopt(Prog *firstp)
 		params.b[z] = 0;
 		consts.b[z] = 0;
 		addrs.b[z] = 0;
+		ivar.b[z] = 0;
 		ovar.b[z] = 0;
 	}
 
-	// build list of return variables
-	setoutvar();
+	// build lists of parameters and results
+	setvar(&ivar, getthis(curfn->type));
+	setvar(&ivar, getinarg(curfn->type));
+	setvar(&ovar, getoutarg(curfn->type));
 
 	/*
 	 * pass 1
@@ -715,8 +716,12 @@ prop(Reg *r, Bits ref, Bits cal)
 		case ACALL:
 			if(noreturn(r1->f.prog))
 				break;
+
+			// Mark all input variables (ivar) as used, because that's what the
+			// liveness bitmaps say. The liveness bitmaps say that so that a
+			// panic will not show stale values in the parameter dump.
 			for(z=0; z<BITS; z++) {
-				cal.b[z] |= ref.b[z] | externs.b[z];
+				cal.b[z] |= ref.b[z] | externs.b[z] | ivar.b[z];
 				ref.b[z] = 0;
 			}
 			
diff --git a/test/fixedbugs/issue7944.go b/test/fixedbugs/issue7944.go
new file mode 100644
index 0000000000..9e5bed1a15
--- /dev/null
+++ b/test/fixedbugs/issue7944.go
@@ -0,0 +1,40 @@
+// run
+
+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 7944:
+// Liveness bitmaps said b was live at call to g,
+// but no one told the register optimizer.
+
+package main
+
+import "runtime"
+
+func f(b []byte) {
+	for len(b) > 0 {
+		n := len(b)
+		n = f1(n)
+		f2(b[n:])
+		b = b[n:]
+	}
+	g()
+}
+
+func f1(n int) int {
+	runtime.GC()
+	return n
+}
+
+func f2(b []byte) {
+	runtime.GC()
+}
+
+func g() {
+	runtime.GC()
+}
+
+func main() {
+	f(make([]byte, 100))
+}