From 6a5f1e58edfe55428d375be26c9c8eefbd67ad31 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Fri, 27 Oct 2017 15:30:19 -0400 Subject: [PATCH] runtime: simplify and optimize typedslicecopy MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Currently, typedslicecopy meticulously performs a typedmemmove on every element of the slice. This probably used to be necessary because we only had an individual element's type, but now we use the heap bitmap, so we only need to know whether the type has any pointers and how big it is. Hence, this CL rewrites typedslicecopy to simply perform one bulk barrier and one memmove. This also has a side-effect of eliminating two unnecessary write barriers per slice element that were coming from updates to dstp and srcp, which were stored in the parent stack frame. However, most of the win comes from eliminating the loops. name old time/op new time/op delta BulkWriteBarrier-12 7.83ns ±10% 7.33ns ± 6% -6.45% (p=0.000 n=20+20) Updates #22460. Change-Id: Id3450e9f36cc8e0892f268319b136f0d8f5464b8 Reviewed-on: https://go-review.googlesource.com/73831 Run-TryBot: Austin Clements TryBot-Result: Gobot Gobot Reviewed-by: Rick Hudson --- src/runtime/mbarrier.go | 40 ++++++---------------------------------- 1 file changed, 6 insertions(+), 34 deletions(-) diff --git a/src/runtime/mbarrier.go b/src/runtime/mbarrier.go index fbead6d378..1183fa91b8 100644 --- a/src/runtime/mbarrier.go +++ b/src/runtime/mbarrier.go @@ -341,41 +341,13 @@ func typedslicecopy(typ *_type, dst, src slice) int { // compiler only emits calls to typedslicecopy for types with pointers, // and growslice and reflect_typedslicecopy check for pointers // before calling typedslicecopy. - if !writeBarrier.needed { - memmove(dstp, srcp, uintptr(n)*typ.size) - return n + size := uintptr(n) * typ.size + if writeBarrier.needed { + bulkBarrierPreWrite(uintptr(dstp), uintptr(srcp), size) } - - systemstack(func() { - if uintptr(srcp) < uintptr(dstp) && uintptr(srcp)+uintptr(n)*typ.size > uintptr(dstp) { - // Overlap with src before dst. - // Copy backward, being careful not to move dstp/srcp - // out of the array they point into. - dstp = add(dstp, uintptr(n-1)*typ.size) - srcp = add(srcp, uintptr(n-1)*typ.size) - i := 0 - for { - typedmemmove(typ, dstp, srcp) - if i++; i >= n { - break - } - dstp = add(dstp, -typ.size) - srcp = add(srcp, -typ.size) - } - } else { - // Copy forward, being careful not to move dstp/srcp - // out of the array they point into. - i := 0 - for { - typedmemmove(typ, dstp, srcp) - if i++; i >= n { - break - } - dstp = add(dstp, typ.size) - srcp = add(srcp, typ.size) - } - } - }) + // See typedmemmove for a discussion of the race between the + // barrier and memmove. + memmove(dstp, srcp, size) return n } -- 2.48.1