cmd/compile, runtime: emit only GC data for stack objects
Currently, for stack objects, the compiler emits metadata that
includes the offset and type descriptor for each object. The type
descriptor symbol has many fields, and it references many other
symbols, e.g. field/element types, equality functions, names.
Observe that what we actually need at runtime is only the GC
metadata that are needed to scan the object, and the GC metadata
are "leaf" symbols (which doesn't reference other symbols). Emit
only the GC data instead. This avoids bringing live the type
descriptor as well as things referenced by it (if it is not
otherwise live).
This reduces binary sizes:
old new
hello (println) 1187776 1133856 (-4.5%)
hello (fmt) 1902448 1844416 (-3.1%)
cmd/compile 22670432 22438576 (-1.0%)
cmd/link 6346272 6225408 (-1.9%)
No significant change in compiler speed.
name old time/op new time/op delta
Template 184ms ± 2% 186ms ± 5% ~ (p=0.905 n=9+10)
Unicode 78.4ms ± 5% 76.3ms ± 3% -2.60% (p=0.009 n=10+10)
GoTypes 1.09s ± 1% 1.08s ± 1% -0.73% (p=0.027 n=10+8)
Compiler 85.6ms ± 3% 84.6ms ± 4% ~ (p=0.143 n=10+10)
SSA 7.23s ± 1% 7.25s ± 1% ~ (p=0.780 n=10+9)
Flate 116ms ± 5% 115ms ± 6% ~ (p=0.912 n=10+10)
GoParser 201ms ± 4% 195ms ± 1% ~ (p=0.089 n=10+10)
Reflect 455ms ± 1% 458ms ± 2% ~ (p=0.050 n=9+9)
Tar 155ms ± 2% 155ms ± 3% ~ (p=0.436 n=10+10)
XML 202ms ± 2% 200ms ± 2% ~ (p=0.053 n=10+9)
Change-Id: I33a7f383d79afba1a482cac6da0cf5b7de9c0ec4
Reviewed-on: https://go-review.googlesource.com/c/go/+/313514
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/src/cmd/compile/internal/liveness/plive.go b/src/cmd/compile/internal/liveness/plive.go
index 424d248..f5c2ef7 100644
--- a/src/cmd/compile/internal/liveness/plive.go
+++ b/src/cmd/compile/internal/liveness/plive.go
@@ -1431,8 +1431,26 @@
// Note: arguments and return values have non-negative Xoffset,
// in which case the offset is relative to argp.
// Locals have a negative Xoffset, in which case the offset is relative to varp.
- off = objw.Uintptr(x, off, uint64(v.FrameOffset()))
- off = objw.SymPtr(x, off, reflectdata.TypeLinksym(v.Type()), 0)
+ // We already limit the frame size, so the offset and the object size
+ // should not be too big.
+ frameOffset := v.FrameOffset()
+ if frameOffset != int64(int32(frameOffset)) {
+ base.Fatalf("frame offset too big: %v %d", v, frameOffset)
+ }
+ off = objw.Uint32(x, off, uint32(frameOffset))
+
+ t := v.Type()
+ sz := t.Width
+ if sz != int64(int32(sz)) {
+ base.Fatalf("stack object too big: %v of type %v, size %d", v, t, sz)
+ }
+ lsym, useGCProg, ptrdata := reflectdata.GCSym(t)
+ if useGCProg {
+ ptrdata = -ptrdata
+ }
+ off = objw.Uint32(x, off, uint32(sz))
+ off = objw.Uint32(x, off, uint32(ptrdata))
+ off = objw.SymPtr(x, off, lsym, 0)
}
if base.Flag.Live != 0 {
diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index 06c4986..01eaf26 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -52,6 +52,9 @@
signatset = make(map[*types.Type]struct{})
signatslice []*types.Type
+ gcsymmu sync.Mutex // protects gcsymset and gcsymslice
+ gcsymset = make(map[*types.Type]struct{})
+
itabs []itabEntry
ptabs []*ir.Name
)
@@ -694,7 +697,8 @@
sptr = writeType(tptr)
}
- gcsym, useGCProg, ptrdata := dgcsym(t)
+ gcsym, useGCProg, ptrdata := dgcsym(t, true)
+ delete(gcsymset, t)
// ../../../../reflect/type.go:/^type.rtype
// actual type structure
@@ -1321,6 +1325,16 @@
}
}
}
+
+ // Emit GC data symbols.
+ gcsyms := make([]typeAndStr, 0, len(gcsymset))
+ for t := range gcsymset {
+ gcsyms = append(gcsyms, typeAndStr{t: t, short: types.TypeSymName(t), regular: t.String()})
+ }
+ sort.Sort(typesByString(gcsyms))
+ for _, ts := range gcsyms {
+ dgcsym(ts.t, true)
+ }
}
func WriteTabs() {
@@ -1490,29 +1504,46 @@
//
const maxPtrmaskBytes = 2048
-// dgcsym emits and returns a data symbol containing GC information for type t,
-// along with a boolean reporting whether the UseGCProg bit should be set in
-// the type kind, and the ptrdata field to record in the reflect type information.
-func dgcsym(t *types.Type) (lsym *obj.LSym, useGCProg bool, ptrdata int64) {
+// GCSym returns a data symbol containing GC information for type t, along
+// with a boolean reporting whether the UseGCProg bit should be set in the
+// type kind, and the ptrdata field to record in the reflect type information.
+// GCSym may be called in concurrent backend, so it does not emit the symbol
+// content.
+func GCSym(t *types.Type) (lsym *obj.LSym, useGCProg bool, ptrdata int64) {
+ // Record that we need to emit the GC symbol.
+ gcsymmu.Lock()
+ if _, ok := gcsymset[t]; !ok {
+ gcsymset[t] = struct{}{}
+ }
+ gcsymmu.Unlock()
+
+ return dgcsym(t, false)
+}
+
+// dgcsym returns a data symbol containing GC information for type t, along
+// with a boolean reporting whether the UseGCProg bit should be set in the
+// type kind, and the ptrdata field to record in the reflect type information.
+// When write is true, it writes the symbol data.
+func dgcsym(t *types.Type, write bool) (lsym *obj.LSym, useGCProg bool, ptrdata int64) {
ptrdata = types.PtrDataSize(t)
if ptrdata/int64(types.PtrSize) <= maxPtrmaskBytes*8 {
- lsym = dgcptrmask(t)
+ lsym = dgcptrmask(t, write)
return
}
useGCProg = true
- lsym, ptrdata = dgcprog(t)
+ lsym, ptrdata = dgcprog(t, write)
return
}
// dgcptrmask emits and returns the symbol containing a pointer mask for type t.
-func dgcptrmask(t *types.Type) *obj.LSym {
+func dgcptrmask(t *types.Type, write bool) *obj.LSym {
ptrmask := make([]byte, (types.PtrDataSize(t)/int64(types.PtrSize)+7)/8)
fillptrmask(t, ptrmask)
p := fmt.Sprintf("runtime.gcbits.%x", ptrmask)
lsym := base.Ctxt.Lookup(p)
- if !lsym.OnList() {
+ if write && !lsym.OnList() {
for i, x := range ptrmask {
objw.Uint8(lsym, i, x)
}
@@ -1549,14 +1580,14 @@
// [types.PtrDataSize(t), t.Width]).
// In practice, the size is types.PtrDataSize(t) except for non-trivial arrays.
// For non-trivial arrays, the program describes the full t.Width size.
-func dgcprog(t *types.Type) (*obj.LSym, int64) {
+func dgcprog(t *types.Type, write bool) (*obj.LSym, int64) {
types.CalcSize(t)
if t.Width == types.BADWIDTH {
base.Fatalf("dgcprog: %v badwidth", t)
}
lsym := TypeLinksymPrefix(".gcprog", t)
var p gcProg
- p.init(lsym)
+ p.init(lsym, write)
p.emit(t, 0)
offset := p.w.BitIndex() * int64(types.PtrSize)
p.end()
@@ -1570,11 +1601,17 @@
lsym *obj.LSym
symoff int
w gcprog.Writer
+ write bool
}
-func (p *gcProg) init(lsym *obj.LSym) {
+func (p *gcProg) init(lsym *obj.LSym, write bool) {
p.lsym = lsym
+ p.write = write && !lsym.OnList()
p.symoff = 4 // first 4 bytes hold program length
+ if !write {
+ p.w.Init(func(byte) {})
+ return
+ }
p.w.Init(p.writeByte)
if base.Debug.GCProg > 0 {
fmt.Fprintf(os.Stderr, "compile: start GCProg for %v\n", lsym)
@@ -1588,6 +1625,9 @@
func (p *gcProg) end() {
p.w.End()
+ if !p.write {
+ return
+ }
objw.Uint32(p.lsym, 0, uint32(p.symoff-4))
objw.Global(p.lsym, int32(p.symoff), obj.DUPOK|obj.RODATA|obj.LOCAL)
p.lsym.Set(obj.AttrContentAddressable, true)
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 719b210..1fd0732 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -792,24 +792,24 @@
if obj == nil {
continue
}
- t := obj.typ
- if t == nil {
+ r := obj.r
+ if r == nil {
// We've already scanned this object.
continue
}
- obj.setType(nil) // Don't scan it again.
+ obj.setRecord(nil) // Don't scan it again.
if stackTraceDebug {
printlock()
- print(" live stkobj at", hex(state.stack.lo+uintptr(obj.off)), "of type", t.string())
+ print(" live stkobj at", hex(state.stack.lo+uintptr(obj.off)), "of size", obj.size)
if conservative {
print(" (conservative)")
}
println()
printunlock()
}
- gcdata := t.gcdata
+ gcdata := r.gcdata
var s *mspan
- if t.kind&kindGCProg != 0 {
+ if r.useGCProg() {
// This path is pretty unlikely, an object large enough
// to have a GC program allocated on the stack.
// We need some space to unpack the program into a straight
@@ -819,15 +819,15 @@
// to change from a Lempel-Ziv style program to something else.
// Or we can forbid putting objects on stacks if they require
// a gc program (see issue 27447).
- s = materializeGCProg(t.ptrdata, gcdata)
+ s = materializeGCProg(r.ptrdata(), gcdata)
gcdata = (*byte)(unsafe.Pointer(s.startAddr))
}
b := state.stack.lo + uintptr(obj.off)
if conservative {
- scanConservative(b, t.ptrdata, gcdata, gcw, &state)
+ scanConservative(b, r.ptrdata(), gcdata, gcw, &state)
} else {
- scanblock(b, t.ptrdata, gcdata, gcw, &state)
+ scanblock(b, r.ptrdata(), gcdata, gcw, &state)
}
if s != nil {
@@ -843,10 +843,10 @@
if stackTraceDebug {
for i := 0; i < x.nobj; i++ {
obj := &x.obj[i]
- if obj.typ == nil { // reachable
+ if obj.r == nil { // reachable
continue
}
- println(" dead stkobj at", hex(gp.stack.lo+uintptr(obj.off)), "of type", obj.typ.string())
+ println(" dead stkobj at", hex(gp.stack.lo+uintptr(obj.off)), "of size", obj.r.size)
// Note: not necessarily really dead - only reachable-from-ptr dead.
}
}
@@ -927,7 +927,7 @@
// varp is 0 for defers, where there are no locals.
// In that case, there can't be a pointer to its args, either.
// (And all args would be scanned above anyway.)
- for _, obj := range objs {
+ for i, obj := range objs {
off := obj.off
base := frame.varp // locals base pointer
if off >= 0 {
@@ -939,9 +939,9 @@
continue
}
if stackTraceDebug {
- println("stkobj at", hex(ptr), "of type", obj.typ.string())
+ println("stkobj at", hex(ptr), "of size", obj.size)
}
- state.addObject(ptr, obj.typ)
+ state.addObject(ptr, &objs[i])
}
}
}
diff --git a/src/runtime/mgcstack.go b/src/runtime/mgcstack.go
index 8eb941a..92d5848 100644
--- a/src/runtime/mgcstack.go
+++ b/src/runtime/mgcstack.go
@@ -150,19 +150,19 @@
//
//go:notinheap
type stackObject struct {
- off uint32 // offset above stack.lo
- size uint32 // size of object
- typ *_type // type info (for ptr/nonptr bits). nil if object has been scanned.
- left *stackObject // objects with lower addresses
- right *stackObject // objects with higher addresses
+ off uint32 // offset above stack.lo
+ size uint32 // size of object
+ r *stackObjectRecord // info of the object (for ptr/nonptr bits). nil if object has been scanned.
+ left *stackObject // objects with lower addresses
+ right *stackObject // objects with higher addresses
}
-// obj.typ = typ, but with no write barrier.
+// obj.r = r, but with no write barrier.
//go:nowritebarrier
-func (obj *stackObject) setType(typ *_type) {
+func (obj *stackObject) setRecord(r *stackObjectRecord) {
// Types of stack objects are always in read-only memory, not the heap.
// So not using a write barrier is ok.
- *(*uintptr)(unsafe.Pointer(&obj.typ)) = uintptr(unsafe.Pointer(typ))
+ *(*uintptr)(unsafe.Pointer(&obj.r)) = uintptr(unsafe.Pointer(r))
}
// A stackScanState keeps track of the state used during the GC walk
@@ -271,7 +271,7 @@
}
// addObject adds a stack object at addr of type typ to the set of stack objects.
-func (s *stackScanState) addObject(addr uintptr, typ *_type) {
+func (s *stackScanState) addObject(addr uintptr, r *stackObjectRecord) {
x := s.tail
if x == nil {
// initial setup
@@ -294,8 +294,8 @@
obj := &x.obj[x.nobj]
x.nobj++
obj.off = uint32(addr - s.stack.lo)
- obj.size = uint32(typ.size)
- obj.setType(typ)
+ obj.size = uint32(r.size)
+ obj.setRecord(r)
// obj.left and obj.right will be initialized by buildIndex before use.
s.nobjs++
}
diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index babfdfc..b21c9c9 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -702,15 +702,15 @@
// we call into morestack.)
continue
}
- t := obj.typ
- gcdata := t.gcdata
+ ptrdata := obj.ptrdata()
+ gcdata := obj.gcdata
var s *mspan
- if t.kind&kindGCProg != 0 {
+ if obj.useGCProg() {
// See comments in mgcmark.go:scanstack
- s = materializeGCProg(t.ptrdata, gcdata)
+ s = materializeGCProg(ptrdata, gcdata)
gcdata = (*byte)(unsafe.Pointer(s.startAddr))
}
- for i := uintptr(0); i < t.ptrdata; i += sys.PtrSize {
+ for i := uintptr(0); i < ptrdata; i += sys.PtrSize {
if *addb(gcdata, i/(8*sys.PtrSize))>>(i/sys.PtrSize&7)&1 != 0 {
adjustpointer(adjinfo, unsafe.Pointer(p+i))
}
@@ -1346,20 +1346,42 @@
abiRegArgsType *_type = efaceOf(&abiRegArgsEface)._type
methodValueCallFrameObjs = []stackObjectRecord{
{
- off: -int(alignUp(abiRegArgsType.size, 8)), // It's always the highest address local.
- typ: abiRegArgsType,
+ off: -int32(alignUp(abiRegArgsType.size, 8)), // It's always the highest address local.
+ size: int32(abiRegArgsType.size),
+ _ptrdata: int32(abiRegArgsType.ptrdata),
+ gcdata: abiRegArgsType.gcdata,
},
}
)
+func init() {
+ if abiRegArgsType.kind&kindGCProg != 0 {
+ throw("abiRegArgsType needs GC Prog, update methodValueCallFrameObjs")
+ }
+}
+
// A stackObjectRecord is generated by the compiler for each stack object in a stack frame.
// This record must match the generator code in cmd/compile/internal/liveness/plive.go:emitStackObjects.
type stackObjectRecord struct {
// offset in frame
// if negative, offset from varp
// if non-negative, offset from argp
- off int
- typ *_type
+ off int32
+ size int32
+ _ptrdata int32 // ptrdata, or -ptrdata is GC prog is used
+ gcdata *byte // pointer map or GC prog of the type
+}
+
+func (r *stackObjectRecord) useGCProg() bool {
+ return r._ptrdata < 0
+}
+
+func (r *stackObjectRecord) ptrdata() uintptr {
+ x := r._ptrdata
+ if x < 0 {
+ return uintptr(-x)
+ }
+ return uintptr(x)
}
// This is exported as ABI0 via linkname so obj can call it.
