cmd/compile: use ,ok return idiom for sparsemap.get

Change-Id: I89719b94de74a32402d02309515dffc4989484db
Reviewed-on: https://go-review.googlesource.com/c/go/+/681575
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@google.com>

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

@@ -56,21 +56,21 @@ func (s *biasedSparseMap) contains(x uint) bool {
 	return s.s.contains(ID(int(x) - s.first))
 }
 
-// get returns the value s maps for key x, or -1 if
-// x is not mapped or is out of range for s.
-func (s *biasedSparseMap) get(x uint) int32 {
+// get returns the value s maps for key x and true, or
+// 0/false if x is not mapped or is out of range for s.
+func (s *biasedSparseMap) get(x uint) (int32, bool) {
 	if s == nil || s.s == nil {
-		return -1
+		return 0, false
 	}
 	if int(x) < s.first {
-		return -1
+		return 0, false
 	}
 	if int(x) >= s.cap() {
-		return -1
+		return 0, false
 	}
 	k := ID(int(x) - s.first)
 	if !s.s.contains(k) {
-		return -1 // TODO: push presence check to callers?
+		return 0, false
 	}
 	return s.s.get(k)
 }

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

@@ -257,7 +257,7 @@ func deadcode(f *Func) {
 	// Find new homes for lost lines -- require earliest in data flow with same line that is also in same block
 	for i := len(order) - 1; i >= 0; i-- {
 		w := order[i]
-		if j := pendingLines.get(w.Pos); j > -1 && f.Blocks[j] == w.Block {
+		if j, ok := pendingLines.get(w.Pos); ok && f.Blocks[j] == w.Block {
 			w.Pos = w.Pos.WithIsStmt()
 			pendingLines.remove(w.Pos)
 		}

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

@@ -118,7 +118,8 @@ func dse(f *Func) {
 					ptr = la
 				}
 			}
-			sr := shadowRange(shadowed.get(ptr.ID))
+			srNum, _ := shadowed.get(ptr.ID)
+			sr := shadowRange(srNum)
 			if sr.contains(off, off+sz) {
 				// Modify the store/zero into a copy of the memory state,
 				// effectively eliding the store operation.

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

@@ -221,7 +221,8 @@ func nilcheckelim2(f *Func) {
 
 				// Iteration order means that first nilcheck in the chain wins, others
 				// are bumped into the ordinary statement preservation algorithm.
-				u := b.Values[unnecessary.get(v.Args[0].ID)]
+				uid, _ := unnecessary.get(v.Args[0].ID)
+				u := b.Values[uid]
 				if !u.Type.IsMemory() && !u.Pos.SameFileAndLine(v.Pos) {
 					if u.Pos.IsStmt() == src.PosIsStmt {
 						pendingLines.add(u.Pos)

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

@@ -199,16 +199,18 @@ func applyRewrite(f *Func, rb blockRewriter, rv valueRewriter, deadcode deadValu
 				f.freeValue(v)
 				continue
 			}
-			if v.Pos.IsStmt() != src.PosNotStmt && !notStmtBoundary(v.Op) && pendingLines.get(vl) == int32(b.ID) {
-				pendingLines.remove(vl)
-				v.Pos = v.Pos.WithIsStmt()
+			if v.Pos.IsStmt() != src.PosNotStmt && !notStmtBoundary(v.Op) {
+				if pl, ok := pendingLines.get(vl); ok && pl == int32(b.ID) {
+					pendingLines.remove(vl)
+					v.Pos = v.Pos.WithIsStmt()
+				}
 			}
 			if i != j {
 				b.Values[j] = v
 			}
 			j++
 		}
-		if pendingLines.get(b.Pos) == int32(b.ID) {
+		if pl, ok := pendingLines.get(b.Pos); ok && pl == int32(b.ID) {
 			b.Pos = b.Pos.WithIsStmt()
 			pendingLines.remove(b.Pos)
 		}

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

@@ -41,13 +41,13 @@ func (s *genericSparseMap[K, V]) contains(k K) bool {
 
 // get returns the value for key k, or the zero V
 // if k does not appear in the map.
-func (s *genericSparseMap[K, V]) get(k K) V {
+func (s *genericSparseMap[K, V]) get(k K) (V, bool) {
 	i := s.sparse[k]
 	if i < int32(len(s.dense)) && s.dense[i].key == k {
-		return s.dense[i].val
+		return s.dense[i].val, true
 	}
 	var v V
-	return v
+	return v, false
 }
 
 func (s *genericSparseMap[K, V]) set(k K, v V) {

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

@@ -69,10 +69,10 @@ func (m *xposmap) set(p src.XPos, v int32) {
 }
 
 // get returns the int32 associated with the file index and line of p.
-func (m *xposmap) get(p src.XPos) int32 {
+func (m *xposmap) get(p src.XPos) (int32, bool) {
 	s := m.mapFor(p.FileIndex())
 	if s == nil {
-		return -1
+		return 0, false
 	}
 	return s.get(p.Line())
 }