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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssagen
import (
"internal/buildcfg"
"internal/race"
"math/rand"
"sort"
"sync"
"time"
"cmd/compile/internal/base"
"cmd/compile/internal/ir"
"cmd/compile/internal/objw"
"cmd/compile/internal/ssa"
"cmd/compile/internal/types"
"cmd/internal/obj"
"cmd/internal/objabi"
"cmd/internal/src"
)
// cmpstackvarlt reports whether the stack variable a sorts before b.
//
// Sort the list of stack variables. Autos after anything else,
// within autos, unused after used, within used, things with
// pointers first, zeroed things first, and then decreasing size.
// Because autos are laid out in decreasing addresses
// on the stack, pointers first, zeroed things first and decreasing size
// really means, in memory, things with pointers needing zeroing at
// the top of the stack and increasing in size.
// Non-autos sort on offset.
func cmpstackvarlt(a, b *ir.Name) bool {
if needAlloc(a) != needAlloc(b) {
return needAlloc(b)
}
if !needAlloc(a) {
return a.FrameOffset() < b.FrameOffset()
}
if a.Used() != b.Used() {
return a.Used()
}
ap := a.Type().HasPointers()
bp := b.Type().HasPointers()
if ap != bp {
return ap
}
ap = a.Needzero()
bp = b.Needzero()
if ap != bp {
return ap
}
if a.Type().Width != b.Type().Width {
return a.Type().Width > b.Type().Width
}
return a.Sym().Name < b.Sym().Name
}
// byStackvar implements sort.Interface for []*Node using cmpstackvarlt.
type byStackVar []*ir.Name
func (s byStackVar) Len() int { return len(s) }
func (s byStackVar) Less(i, j int) bool { return cmpstackvarlt(s[i], s[j]) }
func (s byStackVar) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
// needAlloc reports whether n is within the current frame, for which we need to
// allocate space. In particular, it excludes arguments and results, which are in
// the callers frame.
func needAlloc(n *ir.Name) bool {
return n.Class == ir.PAUTO || n.Class == ir.PPARAMOUT && n.IsOutputParamInRegisters()
}
func (s *ssafn) AllocFrame(f *ssa.Func) {
s.stksize = 0
s.stkptrsize = 0
fn := s.curfn
// Mark the PAUTO's unused.
for _, ln := range fn.Dcl {
if needAlloc(ln) {
ln.SetUsed(false)
}
}
for _, l := range f.RegAlloc {
if ls, ok := l.(ssa.LocalSlot); ok {
ls.N.SetUsed(true)
}
}
for _, b := range f.Blocks {
for _, v := range b.Values {
if n, ok := v.Aux.(*ir.Name); ok {
switch n.Class {
case ir.PPARAMOUT:
if n.IsOutputParamInRegisters() && v.Op == ssa.OpVarDef {
// ignore VarDef, look for "real" uses.
// TODO: maybe do this for PAUTO as well?
continue
}
fallthrough
case ir.PPARAM, ir.PAUTO:
n.SetUsed(true)
}
}
}
}
sort.Sort(byStackVar(fn.Dcl))
// Reassign stack offsets of the locals that are used.
lastHasPtr := false
for i, n := range fn.Dcl {
if n.Op() != ir.ONAME || n.Class != ir.PAUTO && !(n.Class == ir.PPARAMOUT && n.IsOutputParamInRegisters()) {
// i.e., stack assign if AUTO, or if PARAMOUT in registers (which has no predefined spill locations)
continue
}
if !n.Used() {
fn.Dcl = fn.Dcl[:i]
break
}
types.CalcSize(n.Type())
w := n.Type().Width
if w >= types.MaxWidth || w < 0 {
base.Fatalf("bad width")
}
if w == 0 && lastHasPtr {
// Pad between a pointer-containing object and a zero-sized object.
// This prevents a pointer to the zero-sized object from being interpreted
// as a pointer to the pointer-containing object (and causing it
// to be scanned when it shouldn't be). See issue 24993.
w = 1
}
s.stksize += w
s.stksize = types.Rnd(s.stksize, int64(n.Type().Align))
if n.Type().HasPointers() {
s.stkptrsize = s.stksize
lastHasPtr = true
} else {
lastHasPtr = false
}
n.SetFrameOffset(-s.stksize)
}
s.stksize = types.Rnd(s.stksize, int64(types.RegSize))
s.stkptrsize = types.Rnd(s.stkptrsize, int64(types.RegSize))
}
const maxStackSize = 1 << 30
// Compile builds an SSA backend function,
// uses it to generate a plist,
// and flushes that plist to machine code.
// worker indicates which of the backend workers is doing the processing.
func Compile(fn *ir.Func, worker int) {
f := buildssa(fn, worker)
// Note: check arg size to fix issue 25507.
if f.Frontend().(*ssafn).stksize >= maxStackSize || f.OwnAux.ArgWidth() >= maxStackSize {
largeStackFramesMu.Lock()
largeStackFrames = append(largeStackFrames, largeStack{locals: f.Frontend().(*ssafn).stksize, args: f.OwnAux.ArgWidth(), pos: fn.Pos()})
largeStackFramesMu.Unlock()
return
}
pp := objw.NewProgs(fn, worker)
defer pp.Free()
genssa(f, pp)
// Check frame size again.
// The check above included only the space needed for local variables.
// After genssa, the space needed includes local variables and the callee arg region.
// We must do this check prior to calling pp.Flush.
// If there are any oversized stack frames,
// the assembler may emit inscrutable complaints about invalid instructions.
if pp.Text.To.Offset >= maxStackSize {
largeStackFramesMu.Lock()
locals := f.Frontend().(*ssafn).stksize
largeStackFrames = append(largeStackFrames, largeStack{locals: locals, args: f.OwnAux.ArgWidth(), callee: pp.Text.To.Offset - locals, pos: fn.Pos()})
largeStackFramesMu.Unlock()
return
}
pp.Flush() // assemble, fill in boilerplate, etc.
// fieldtrack must be called after pp.Flush. See issue 20014.
fieldtrack(pp.Text.From.Sym, fn.FieldTrack)
}
func init() {
if race.Enabled {
rand.Seed(time.Now().UnixNano())
}
}
// StackOffset returns the stack location of a LocalSlot relative to the
// stack pointer, suitable for use in a DWARF location entry. This has nothing
// to do with its offset in the user variable.
func StackOffset(slot ssa.LocalSlot) int32 {
n := slot.N
var off int64
switch n.Class {
case ir.PPARAM, ir.PPARAMOUT:
if !n.IsOutputParamInRegisters() {
off = n.FrameOffset() + base.Ctxt.FixedFrameSize()
break
}
fallthrough // PPARAMOUT in registers allocates like an AUTO
case ir.PAUTO:
off = n.FrameOffset()
if base.Ctxt.FixedFrameSize() == 0 {
off -= int64(types.PtrSize)
}
if buildcfg.FramePointerEnabled {
off -= int64(types.PtrSize)
}
}
return int32(off + slot.Off)
}
// fieldtrack adds R_USEFIELD relocations to fnsym to record any
// struct fields that it used.
func fieldtrack(fnsym *obj.LSym, tracked map[*obj.LSym]struct{}) {
if fnsym == nil {
return
}
if !buildcfg.Experiment.FieldTrack || len(tracked) == 0 {
return
}
trackSyms := make([]*obj.LSym, 0, len(tracked))
for sym := range tracked {
trackSyms = append(trackSyms, sym)
}
sort.Slice(trackSyms, func(i, j int) bool { return trackSyms[i].Name < trackSyms[j].Name })
for _, sym := range trackSyms {
r := obj.Addrel(fnsym)
r.Sym = sym
r.Type = objabi.R_USEFIELD
}
}
// largeStack is info about a function whose stack frame is too large (rare).
type largeStack struct {
locals int64
args int64
callee int64
pos src.XPos
}
var (
largeStackFramesMu sync.Mutex // protects largeStackFrames
largeStackFrames []largeStack
)
func CheckLargeStacks() {
// Check whether any of the functions we have compiled have gigantic stack frames.
sort.Slice(largeStackFrames, func(i, j int) bool {
return largeStackFrames[i].pos.Before(largeStackFrames[j].pos)
})
for _, large := range largeStackFrames {
if large.callee != 0 {
base.ErrorfAt(large.pos, "stack frame too large (>1GB): %d MB locals + %d MB args + %d MB callee", large.locals>>20, large.args>>20, large.callee>>20)
} else {
base.ErrorfAt(large.pos, "stack frame too large (>1GB): %d MB locals + %d MB args", large.locals>>20, large.args>>20)
}
}
}