Optimize/eliminate bounds checking

TODO: do better at it by tracking min/max values of integers. The
following straightforward code doesn't have its bounds checks removed:

    for _, n := range slice {
        println(n)
    }

src/runtime/hashmap.go

@@ -66,6 +66,7 @@ func hashmapMake(keySize, valueSize uint8) *hashmap {
 }
 
 // Set a specified key to a given value. Grow the map if necessary.
+//go:nobounds
 func hashmapSet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint32, keyEqual func(x, y unsafe.Pointer, n uintptr) bool) {
 	numBuckets := uintptr(1) << m.bucketBits
 	bucketNumber := (uintptr(hash) & (numBuckets - 1))
@@ -114,6 +115,7 @@ func hashmapSet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint3
 }
 
 // Get the value of a specified key, or zero the value if not found.
+//go:nobounds
 func hashmapGet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint32, keyEqual func(x, y unsafe.Pointer, n uintptr) bool) {
 	numBuckets := uintptr(1) << m.bucketBits
 	bucketNumber := (uintptr(hash) & (numBuckets - 1))

src/runtime/interface.go

@@ -44,6 +44,7 @@ var (
 
 // Get the function pointer for the method on the interface.
 // This is a compiler intrinsic.
+//go:nobounds
 func interfaceMethod(itf _interface, method uint16) *uint8 {
 	// This function doesn't do bounds checking as the supplied method must be
 	// in the list of signatures. The compiler will only emit

src/runtime/print.go

@@ -4,6 +4,7 @@ import (
 	"unsafe"
 )
 
+//go:nobounds
 func printstring(s string) {
 	for i := 0; i < len(s); i++ {
 		putchar(s[i])
@@ -42,6 +43,7 @@ func printint16(n uint16) {
 	printint32(int32(n))
 }
 
+//go:nobounds
 func printuint32(n uint32) {
 	digits := [10]byte{} // enough to hold (2^32)-1
 	// Fill in all 10 digits.

src/runtime/runtime.go

@@ -56,7 +56,7 @@ func _panic(message interface{}) {
 	abort()
 }
 
-// Check for bounds in *ssa.IndexAddr and *ssa.Lookup.
+// Check for bounds in *ssa.Index, *ssa.IndexAddr and *ssa.Lookup.
 func lookupBoundsCheck(length, index int) {
 	if index < 0 || index >= length {
 		// printstring() here is safe as this function is excluded from bounds

src/runtime/string.go

@@ -13,6 +13,7 @@ type _string struct {
 }
 
 // Return true iff the strings match.
+//go:nobounds
 func stringEqual(x, y string) bool {
 	if len(x) != len(y) {
 		return false