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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>
This commit is contained in:
Rick Hudson 2015-04-22 15:06:35 -04:00
parent aef54d40ac
commit 77f56af0bc
1 changed files with 4 additions and 4 deletions
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8
src/runtime/mgcmark.go
View File

@ -596,11 +596,14 @@ func scanobject(b, n uintptr, ptrmask *uint8, gcw *gcWork) {
// 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 @@ func scanobject(b, n uintptr, ptrmask *uint8, gcw *gcWork) {
// 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