libgo: update to Go1.16beta1 release

This does not yet include support for the //go:embed directive added
in this release.

	* Makefile.am (check-runtime): Don't create check-runtime-dir.
	(mostlyclean-local): Don't remove check-runtime-dir.
	(check-go-tool, check-vet): Copy in go.mod and modules.txt.
	(check-cgo-test, check-carchive-test): Add go.mod file.
	* Makefile.in: Regenerate.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/280172

1 files changed, 28 insertions, 190 deletions

diff --git a/libgo/go/runtime/mgcmark.go b/libgo/go/runtime/mgcmark.go
index 4e4d131..ed2a8c1 100644
--- a/libgo/go/runtime/mgcmark.go
+++ b/libgo/go/runtime/mgcmark.go
@@ -47,10 +47,6 @@ const (
 	// Must be a multiple of the pageInUse bitmap element size and
 	// must also evenly divide pagesPerArena.
 	pagesPerSpanRoot = 512
-
-	// go115NewMarkrootSpans is a feature flag that indicates whether
-	// to use the new bitmap-based markrootSpans implementation.
-	go115NewMarkrootSpans = true
 )
 
 // gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
@@ -58,6 +54,8 @@ const (
 //
 // The world must be stopped.
 func gcMarkRootPrepare() {
+	assertWorldStopped()
+
 	work.nFlushCacheRoots = 0
 
 	work.nDataRoots = 0
@@ -73,24 +71,16 @@ func gcMarkRootPrepare() {
 	//
 	// We depend on addfinalizer to mark objects that get
 	// finalizers after root marking.
-	if go115NewMarkrootSpans {
-		// We're going to scan the whole heap (that was available at the time the
-		// mark phase started, i.e. markArenas) for in-use spans which have specials.
-		//
-		// Break up the work into arenas, and further into chunks.
-		//
-		// Snapshot allArenas as markArenas. This snapshot is safe because allArenas
-		// is append-only.
-		mheap_.markArenas = mheap_.allArenas[:len(mheap_.allArenas):len(mheap_.allArenas)]
-		work.nSpanRoots = len(mheap_.markArenas) * (pagesPerArena / pagesPerSpanRoot)
-	} else {
-		// We're only interested in scanning the in-use spans,
-		// which will all be swept at this point. More spans
-		// may be added to this list during concurrent GC, but
-		// we only care about spans that were allocated before
-		// this mark phase.
-		work.nSpanRoots = mheap_.sweepSpans[mheap_.sweepgen/2%2].numBlocks()
-	}
+	//
+	// We're going to scan the whole heap (that was available at the time the
+	// mark phase started, i.e. markArenas) for in-use spans which have specials.
+	//
+	// Break up the work into arenas, and further into chunks.
+	//
+	// Snapshot allArenas as markArenas. This snapshot is safe because allArenas
+	// is append-only.
+	mheap_.markArenas = mheap_.allArenas[:len(mheap_.allArenas):len(mheap_.allArenas)]
+	work.nSpanRoots = len(mheap_.markArenas) * (pagesPerArena / pagesPerSpanRoot)
 
 	// Scan stacks.
 	//
@@ -252,10 +242,6 @@ func markrootBlock(roots *gcRootList, gcw *gcWork) {
 //
 //go:nowritebarrier
 func markrootSpans(gcw *gcWork, shard int) {
-	if !go115NewMarkrootSpans {
-		oldMarkrootSpans(gcw, shard)
-		return
-	}
 	// Objects with finalizers have two GC-related invariants:
 	//
 	// 1) Everything reachable from the object must be marked.
@@ -332,90 +318,6 @@ func markrootSpans(gcw *gcWork, shard int) {
 	}
 }
 
-// oldMarkrootSpans marks roots for one shard of work.spans.
-//
-// For go115NewMarkrootSpans = false.
-//
-//go:nowritebarrier
-func oldMarkrootSpans(gcw *gcWork, shard int) {
-	// Objects with finalizers have two GC-related invariants:
-	//
-	// 1) Everything reachable from the object must be marked.
-	// This ensures that when we pass the object to its finalizer,
-	// everything the finalizer can reach will be retained.
-	//
-	// 2) Finalizer specials (which are not in the garbage
-	// collected heap) are roots. In practice, this means the fn
-	// field must be scanned.
-	//
-	// TODO(austin): There are several ideas for making this more
-	// efficient in issue #11485.
-
-	sg := mheap_.sweepgen
-	spans := mheap_.sweepSpans[mheap_.sweepgen/2%2].block(shard)
-	// Note that work.spans may not include spans that were
-	// allocated between entering the scan phase and now. We may
-	// also race with spans being added into sweepSpans when they're
-	// just created, and as a result we may see nil pointers in the
-	// spans slice. This is okay because any objects with finalizers
-	// in those spans must have been allocated and given finalizers
-	// after we entered the scan phase, so addfinalizer will have
-	// ensured the above invariants for them.
-	for i := 0; i < len(spans); i++ {
-		// sweepBuf.block requires that we read pointers from the block atomically.
-		// It also requires that we ignore nil pointers.
-		s := (*mspan)(atomic.Loadp(unsafe.Pointer(&spans[i])))
-
-		// This is racing with spans being initialized, so
-		// check the state carefully.
-		if s == nil || s.state.get() != mSpanInUse {
-			continue
-		}
-		// Check that this span was swept (it may be cached or uncached).
-		if !useCheckmark && !(s.sweepgen == sg || s.sweepgen == sg+3) {
-			// sweepgen was updated (+2) during non-checkmark GC pass
-			print("sweep ", s.sweepgen, " ", sg, "\n")
-			throw("gc: unswept span")
-		}
-
-		// Speculatively check if there are any specials
-		// without acquiring the span lock. This may race with
-		// adding the first special to a span, but in that
-		// case addfinalizer will observe that the GC is
-		// active (which is globally synchronized) and ensure
-		// the above invariants. We may also ensure the
-		// invariants, but it's okay to scan an object twice.
-		if s.specials == nil {
-			continue
-		}
-
-		// Lock the specials to prevent a special from being
-		// removed from the list while we're traversing it.
-		lock(&s.speciallock)
-
-		for sp := s.specials; sp != nil; sp = sp.next {
-			if sp.kind != _KindSpecialFinalizer {
-				continue
-			}
-			// don't mark finalized object, but scan it so we
-			// retain everything it points to.
-			spf := (*specialfinalizer)(unsafe.Pointer(sp))
-			// A finalizer can be set for an inner byte of an object, find object beginning.
-			p := s.base() + uintptr(spf.special.offset)/s.elemsize*s.elemsize
-
-			// Mark everything that can be reached from
-			// the object (but *not* the object itself or
-			// we'll never collect it).
-			scanobject(p, gcw)
-
-			// The special itself is a root.
-			scanblock(uintptr(unsafe.Pointer(&spf.fn)), sys.PtrSize, &oneptrmask[0], gcw)
-		}
-
-		unlock(&s.speciallock)
-	}
-}
-
 // gcAssistAlloc performs GC work to make gp's assist debt positive.
 // gp must be the calling user gorountine.
 //
@@ -436,11 +338,13 @@ retry:
 	// balance positive. When the required amount of work is low,
 	// we over-assist to build up credit for future allocations
 	// and amortize the cost of assisting.
+	assistWorkPerByte := float64frombits(atomic.Load64(&gcController.assistWorkPerByte))
+	assistBytesPerWork := float64frombits(atomic.Load64(&gcController.assistBytesPerWork))
 	debtBytes := -gp.gcAssistBytes
-	scanWork := int64(gcController.assistWorkPerByte * float64(debtBytes))
+	scanWork := int64(assistWorkPerByte * float64(debtBytes))
 	if scanWork < gcOverAssistWork {
 		scanWork = gcOverAssistWork
-		debtBytes = int64(gcController.assistBytesPerWork * float64(scanWork))
+		debtBytes = int64(assistBytesPerWork * float64(scanWork))
 	}
 
 	// Steal as much credit as we can from the background GC's
@@ -454,7 +358,7 @@ retry:
 	if bgScanCredit > 0 {
 		if bgScanCredit < scanWork {
 			stolen = bgScanCredit
-			gp.gcAssistBytes += 1 + int64(gcController.assistBytesPerWork*float64(stolen))
+			gp.gcAssistBytes += 1 + int64(assistBytesPerWork*float64(stolen))
 		} else {
 			stolen = scanWork
 			gp.gcAssistBytes += debtBytes
@@ -579,7 +483,8 @@ func gcAssistAlloc1(gp *g, scanWork int64) {
 	// this scan work counts for. The "1+" is a poor man's
 	// round-up, to ensure this adds credit even if
 	// assistBytesPerWork is very low.
-	gp.gcAssistBytes += 1 + int64(gcController.assistBytesPerWork*float64(workDone))
+	assistBytesPerWork := float64frombits(atomic.Load64(&gcController.assistBytesPerWork))
+	gp.gcAssistBytes += 1 + int64(assistBytesPerWork*float64(workDone))
 
 	// If this is the last worker and we ran out of work,
 	// signal a completion point.
@@ -673,7 +578,8 @@ func gcFlushBgCredit(scanWork int64) {
 		return
 	}
 
-	scanBytes := int64(float64(scanWork) * gcController.assistBytesPerWork)
+	assistBytesPerWork := float64frombits(atomic.Load64(&gcController.assistBytesPerWork))
+	scanBytes := int64(float64(scanWork) * assistBytesPerWork)
 
 	lock(&work.assistQueue.lock)
 	for !work.assistQueue.q.empty() && scanBytes > 0 {
@@ -706,7 +612,8 @@ func gcFlushBgCredit(scanWork int64) {
 
 	if scanBytes > 0 {
 		// Convert from scan bytes back to work.
-		scanWork = int64(float64(scanBytes) * gcController.assistWorkPerByte)
+		assistWorkPerByte := float64frombits(atomic.Load64(&gcController.assistWorkPerByte))
+		scanWork = int64(float64(scanBytes) * assistWorkPerByte)
 		atomic.Xaddint64(&gcController.bgScanCredit, scanWork)
 	}
 	unlock(&work.assistQueue.lock)
@@ -1154,11 +1061,7 @@ func scanobject(b uintptr, gcw *gcWork) {
 		}
 		// Load bits once. See CL 22712 and issue 16973 for discussion.
 		bits := hbits.bits()
-		// During checkmarking, 1-word objects store the checkmark
-		// in the type bit for the one word. The only one-word objects
-		// are pointers, or else they'd be merged with other non-pointer
-		// data into larger allocations.
-		if i != 1*sys.PtrSize && bits&bitScan == 0 {
+		if bits&bitScan == 0 {
 			break // no more pointers in this object
 		}
 		if bits&bitPointer == 0 {
@@ -1280,35 +1183,10 @@ func greyobject(obj, base, off uintptr, span *mspan, gcw *gcWork, objIndex uintp
 	mbits := span.markBitsForIndex(objIndex)
 
 	if useCheckmark {
-		if !mbits.isMarked() {
-			// Stack scanning is conservative, so we can
-			// see a reference to an object not previously
-			// found. Assume the object was correctly not
-			// marked and ignore the pointer.
-			if forStack {
-				return
-			}
-			printlock()
-			print("runtime:greyobject: checkmarks finds unexpected unmarked object obj=", hex(obj), "\n")
-			print("runtime: found obj at *(", hex(base), "+", hex(off), ")\n")
-
-			// Dump the source (base) object
-			gcDumpObject("base", base, off)
-
-			// Dump the object
-			gcDumpObject("obj", obj, ^uintptr(0))
-
-			getg().m.traceback = 2
-			throw("checkmark found unmarked object")
-		}
-		hbits := heapBitsForAddr(obj)
-		if hbits.isCheckmarked(span.elemsize) {
+		if setCheckmark(obj, base, off, mbits, forStack) {
+			// Already marked.
 			return
 		}
-		hbits.setCheckmarked(span.elemsize)
-		if !hbits.isCheckmarked(span.elemsize) {
-			throw("setCheckmarked and isCheckmarked disagree")
-		}
 	} else {
 		// Stack scanning is conservative, so we can see a
 		// pointer to a free object. Assume the object was
@@ -1434,6 +1312,8 @@ func gcmarknewobject(span *mspan, obj, size, scanSize uintptr) {
 //
 // The world must be stopped.
 func gcMarkTinyAllocs() {
+	assertWorldStopped()
+
 	for _, p := range allp {
 		c := p.mcache
 		if c == nil || c.tiny == 0 {
@@ -1444,45 +1324,3 @@ func gcMarkTinyAllocs() {
 		greyobject(c.tiny, 0, 0, span, gcw, objIndex, false)
 	}
 }
-
-// Checkmarking
-
-// To help debug the concurrent GC we remark with the world
-// stopped ensuring that any object encountered has their normal
-// mark bit set. To do this we use an orthogonal bit
-// pattern to indicate the object is marked. The following pattern
-// uses the upper two bits in the object's boundary nibble.
-// 01: scalar  not marked
-// 10: pointer not marked
-// 11: pointer     marked
-// 00: scalar      marked
-// Xoring with 01 will flip the pattern from marked to unmarked and vica versa.
-// The higher bit is 1 for pointers and 0 for scalars, whether the object
-// is marked or not.
-// The first nibble no longer holds the typeDead pattern indicating that the
-// there are no more pointers in the object. This information is held
-// in the second nibble.
-
-// If useCheckmark is true, marking of an object uses the
-// checkmark bits (encoding above) instead of the standard
-// mark bits.
-var useCheckmark = false
-
-//go:nowritebarrier
-func initCheckmarks() {
-	useCheckmark = true
-	for _, s := range mheap_.allspans {
-		if s.state.get() == mSpanInUse {
-			heapBitsForAddr(s.base()).initCheckmarkSpan(s.layout())
-		}
-	}
-}
-
-func clearCheckmarks() {
-	useCheckmark = false
-	for _, s := range mheap_.allspans {
-		if s.state.get() == mSpanInUse {
-			heapBitsForAddr(s.base()).clearCheckmarkSpan(s.layout())
-		}
-	}
-}