runtime: Improve scanning performance
To achieve a 2% improvement in the garbage benchmark this CL removes
an unneeded assert and avoids one hbits.next() call per object
being scanned.
Change-Id: Ibd542d01e9c23eace42228886f9edc488354df0d
Reviewed-on: https://go-review.googlesource.com/9244
Reviewed-by: Austin Clements <austin@google.com>
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index c53747c..4afdca4 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -596,11 +596,14 @@
// dense mask (stack or data)
bits = (uintptr(*(*byte)(add(unsafe.Pointer(ptrmask), (i/ptrSize)/4))) >> (((i / ptrSize) % 4) * typeBitsWidth)) & typeMask
} else {
+ if i != 0 {
+ // Avoid needless hbits.next() on last iteration.
+ hbits = hbits.next()
+ }
bits = uintptr(hbits.typeBits())
if bits == typeDead {
break // no more pointers in this object
}
- hbits = hbits.next()
}
if bits <= typeScalar { // typeScalar, typeDead, typeScalarMarked
@@ -647,9 +650,6 @@
// The object is not nil and known to be in the heap.
//go:nowritebarrier
func shade(b uintptr) {
- if !inheap(b) {
- throw("shade: passed an address not in the heap")
- }
if obj, hbits, span := heapBitsForObject(b); obj != 0 {
// TODO: this would be a great place to put a check to see
// if we are harvesting and if we are then we should
