cmd/compile/internal: reuse more memory

Reuse even more memory, and keep track of it in a long-lived debugState
object rather than piecemeal in the Cache.

Change-Id: Ib6936b4e8594dc6dda1f59ece753c00fd1c136ba
Reviewed-on: https://go-review.googlesource.com/92404Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/fmt_test.go

@@ -572,7 +572,6 @@ var knownFormats = map[string]string{
 	"*cmd/compile/internal/ssa.Block %v":              "",
 	"*cmd/compile/internal/ssa.Func %s":               "",
 	"*cmd/compile/internal/ssa.Func %v":               "",
-	"*cmd/compile/internal/ssa.LocalSlot %v":          "",
 	"*cmd/compile/internal/ssa.Register %s":           "",
 	"*cmd/compile/internal/ssa.Register %v":           "",
 	"*cmd/compile/internal/ssa.SparseTreeNode %v":     "",

src/cmd/compile/internal/gc/pgen.go

@@ -650,7 +650,7 @@ func createComplexVar(fn *Func, varID ssa.VarID) *dwarf.Var {
 		// variables just give it the first 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: stackOffset(*debug.Slots[debug.VarSlots[varID][0]]),
+		StackOffset: stackOffset(debug.Slots[debug.VarSlots[varID][0]]),
 		DeclFile:    declpos.RelFilename(),
 		DeclLine:    declpos.RelLine(),
 		DeclCol:     declpos.Col(),

src/cmd/compile/internal/ssa/cache.go

@@ -25,15 +25,7 @@ type Cache struct {
 	scrSparse     []*sparseSet // scratch sparse sets to be re-used.
 
 	ValueToProgAfter []*obj.Prog
-	blockDebug       []BlockDebug
-	valueNames       [][]SlotID
-	slotLocs         []VarLoc
-	regContents      [][]SlotID
-	pendingEntries   []pendingEntry
-	pendingSlotLocs  []VarLoc
-
-	liveSlotSliceBegin int
-	liveSlots          []liveSlot
+	debugState       debugState
 }
 
 func (c *Cache) Reset() {
@@ -53,16 +45,5 @@ func (c *Cache) Reset() {
 		xl[i] = nil
 	}
 
-	c.liveSlots = c.liveSlots[:0]
-	c.liveSlotSliceBegin = 0
-}
-
-func (c *Cache) AppendLiveSlot(ls liveSlot) {
-	c.liveSlots = append(c.liveSlots, ls)
 }
 
-func (c *Cache) GetLiveSlotSlice() []liveSlot {
-	s := c.liveSlots[c.liveSlotSliceBegin:]
-	c.liveSlotSliceBegin = len(c.liveSlots)
-	return s
-}