Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

cmd/compile: use correct stack slots in location lists

Browse source 
When variables need to be spilled to the stack, they usually get their
own stack slot. Local variables have a slot allocated if they need one,
and arguments start out on the stack. Before this CL, the debug
information made the assumption that this was always the case, and so
didn't bother storing an actual stack offset during SSA analysis.

There's at least one case where this isn't true: variables that alias
arguments. Since the argument is the source of the variable, the
variable will begin its life on the stack in the argument's stack slot,
not its own. Therefore the debug info needs to track the actual stack
slot for each location entry.

No detectable performance change, despite the O(N) loop in getHomeSlot.

Change-Id: I2701adb7eddee17d4524336cb7aa6786e8f32b46
Reviewed-on: https://go-review.googlesource.com/67231
Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Heschi Kreinick 2017-09-29 14:14:03 -04:00
parent ca8c361d86
commit 0b6b5641d7
2 changed files with 80 additions and 26 deletions
Download patch file Download diff file Expand all files Collapse all files

41
src/cmd/compile/internal/gc/pgen.go
View file

@ -437,7 +437,7 @@ func createComplexVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug) ([]*Node, []*d
// Group SSA variables by the user variable they were decomposed from.
varParts := map[*Node][]varPart{}
for slotID, slot := range debugInfo.Slots {
for slotID, slot := range debugInfo.VarSlots {
for slot.SplitOf != nil {
slot = slot.SplitOf
}
@ -450,7 +450,7 @@ func createComplexVars(fnsym *obj.LSym, debugInfo *ssa.FuncDebug) ([]*Node, []*d
// createComplexVar has side effects. Instead, go by slot.
var decls []*Node
var vars []*dwarf.Var
for _, slot := range debugInfo.Slots {
for _, slot := range debugInfo.VarSlots {
for slot.SplitOf != nil {
slot = slot.SplitOf
}
@ -490,6 +490,26 @@ func (a partsByVarOffset) Len() int { return len(a) }
func (a partsByVarOffset) Less(i, j int) bool { return a[i].varOffset < a[j].varOffset }
func (a partsByVarOffset) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
// 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.(*Node)
var base int64
switch n.Class() {
case PAUTO:
if Ctxt.FixedFrameSize() == 0 {
base -= int64(Widthptr)
}
if objabi.Framepointer_enabled(objabi.GOOS, objabi.GOARCH) {
base -= int64(Widthptr)
}
case PPARAM, PPARAMOUT:
base += Ctxt.FixedFrameSize()
}
return int32(base + n.Xoffset + slot.Off)
}
// createComplexVar builds a DWARF variable entry and location list representing n.
func createComplexVar(debugInfo *ssa.FuncDebug, n *Node, parts []varPart) *dwarf.Var {
slots := debugInfo.Slots
@ -514,14 +534,15 @@ func createComplexVar(debugInfo *ssa.FuncDebug, n *Node, parts []varPart) *dwarf
gotype := ngotype(n).Linksym()
typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
// The stack offset is used as a sorting key, so for decomposed
// variables just give it the lowest one. It's not used otherwise.
stackOffset := debugInfo.Slots[parts[0].slot].N.(*Node).Xoffset + offs
dvar := &dwarf.Var{
Name: n.Sym.Name,
Abbrev: abbrev,
Type: Ctxt.Lookup(typename),
StackOffset: int32(stackOffset),
Name: n.Sym.Name,
Abbrev: abbrev,
Type: Ctxt.Lookup(typename),
// The stack offset is used as a sorting key, so for decomposed
// variables just give it the lowest one. It's not used otherwise.
// This won't work well if the first slot hasn't been assigned a stack
// location, but it's not obvious how to do better.
StackOffset: int32(stackOffset(slots[parts[0].slot])),
DeclLine: n.Pos.Line(),
}
@ -666,7 +687,7 @@ func createComplexVar(debugInfo *ssa.FuncDebug, n *Node, parts []varPart) *dwarf
}
if loc.OnStack {
dpiece.OnStack = true
dpiece.StackOffset = int32(offs + slots[part.slot].Off + slots[part.slot].N.(*Node).Xoffset)
dpiece.StackOffset = stackOffset(slots[loc.StackLocation])
} else {
for reg := 0; reg < len(debugInfo.Registers); reg++ {
if loc.Registers&(1<<uint8(reg)) != 0 {