internal/maps,cmd/compile/internal/walk: replace calls to mapaccess1* with mapaccess2*

mapaccess1* and mapaccess2* functions share the same implementation and differ only in whether the boolean "found" is returned.

This change replaces mapaccess1* calls with mapaccess2*.
We can do this transparently, since the call site can safely discard the second (boolean) result.

Ideally, mapacces1* functions could be removed entirely, but this change keeps them as thin wrappers for compatibility.

Fixes #73196
Change-Id: I07c3423d22ed1095ac3666d00e134c2747b2f9c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/736020
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>

3 files changed, 44 insertions, 21 deletions

diff --git a/src/cmd/compile/internal/walk/assign.go b/src/cmd/compile/internal/walk/assign.go
index 63b6a1d2c1..f640cd83d1 100644
--- a/src/cmd/compile/internal/walk/assign.go
+++ b/src/cmd/compile/internal/walk/assign.go
@@ -154,12 +154,14 @@ func walkAssignMapRead(init *ir.Nodes, n *ir.AssignListStmt) ir.Node {
 
 	r := n.Rhs[0].(*ir.IndexExpr)
 	walkExprListSafe(n.Lhs, init)
+
 	r.X = walkExpr(r.X, init)
 	r.Index = walkExpr(r.Index, init)
+	map_ := r.X
 	t := r.X.Type()
-
 	fast := mapfast(t)
 	key := mapKeyArg(fast, r, r.Index, false)
+	args := []ir.Node{reflectdata.IndexMapRType(base.Pos, r), map_, key}
 
 	// from:
 	//   a,b = m[i]
@@ -168,15 +170,14 @@ func walkAssignMapRead(init *ir.Nodes, n *ir.AssignListStmt) ir.Node {
 	//   a = *var
 	a := n.Lhs[0]
 
-	var call *ir.CallExpr
-	if w := t.Elem().Size(); w <= abi.ZeroValSize {
-		fn := mapfn(mapaccess2[fast], t, false)
-		call = mkcall1(fn, fn.Type().ResultsTuple(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key)
+	var mapFn ir.Node
+	if t.Elem().Size() > abi.ZeroValSize {
+		args = append(args, reflectdata.ZeroAddr(t.Elem().Size()))
+		mapFn = mapfn("mapaccess2_fat", t, true)
 	} else {
-		fn := mapfn("mapaccess2_fat", t, true)
-		z := reflectdata.ZeroAddr(w)
-		call = mkcall1(fn, fn.Type().ResultsTuple(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key, z)
+		mapFn = mapfn(mapaccess[fast], t, false)
 	}
+	call := mkcall1(mapFn, mapFn.Type().ResultsTuple(), init, args...)
 
 	// mapaccess2* returns a typed bool, but due to spec changes,
 	// the boolean result of i.(T) is now untyped so we make it the
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index 2794671c73..125ffd53b1 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -868,20 +868,43 @@ func walkIndexMap(n *ir.IndexExpr, init *ir.Nodes) ir.Node {
 	key := mapKeyArg(fast, n, n.Index, n.Assigned)
 	args := []ir.Node{reflectdata.IndexMapRType(base.Pos, n), map_, key}
 
+	if n.Assigned {
+		mapFn := mapfn(mapassign[fast], t, false)
+		call := mkcall1(mapFn, nil, init, args...)
+		call.SetType(types.NewPtr(t.Elem()))
+		call.MarkNonNil() // mapassign always return non-nil pointers.
+		star := ir.NewStarExpr(base.Pos, call)
+		star.SetType(t.Elem())
+		star.SetTypecheck(1)
+		return star
+	}
+
+	// from:
+	//   m[i]
+	// to:
+	//   var, _ = mapaccess2*(t, m, i)
+	//   *var
 	var mapFn ir.Node
-	switch {
-	case n.Assigned:
-		mapFn = mapfn(mapassign[fast], t, false)
-	case t.Elem().Size() > abi.ZeroValSize:
+	if t.Elem().Size() > abi.ZeroValSize {
 		args = append(args, reflectdata.ZeroAddr(t.Elem().Size()))
-		mapFn = mapfn("mapaccess1_fat", t, true)
-	default:
-		mapFn = mapfn(mapaccess1[fast], t, false)
+		mapFn = mapfn("mapaccess2_fat", t, true)
+	} else {
+		mapFn = mapfn(mapaccess[fast], t, false)
 	}
-	call := mkcall1(mapFn, nil, init, args...)
-	call.SetType(types.NewPtr(t.Elem()))
-	call.MarkNonNil() // mapaccess1* and mapassign always return non-nil pointers.
-	star := ir.NewStarExpr(base.Pos, call)
+	call := mkcall1(mapFn, mapFn.Type().ResultsTuple(), init, args...)
+
+	var_ := typecheck.TempAt(base.Pos, ir.CurFunc, types.NewPtr(t.Elem()))
+	var_.SetTypecheck(1)
+	var_.MarkNonNil() // mapaccess always returns a non-nill pointer
+
+	bool_ := typecheck.TempAt(base.Pos, ir.CurFunc, types.Types[types.TBOOL])
+	bool_.SetTypecheck(1)
+
+	r := ir.NewAssignListStmt(base.Pos, ir.OAS2FUNC, []ir.Node{var_, bool_}, []ir.Node{call})
+	r.SetTypecheck(1)
+	init.Append(walkExpr(r, init))
+
+	star := ir.NewStarExpr(base.Pos, var_)
 	star.SetType(t.Elem())
 	star.SetTypecheck(1)
 	return star
diff --git a/src/cmd/compile/internal/walk/walk.go b/src/cmd/compile/internal/walk/walk.go
index 08f36095a5..a97263d2bf 100644
--- a/src/cmd/compile/internal/walk/walk.go
+++ b/src/cmd/compile/internal/walk/walk.go
@@ -184,8 +184,7 @@ func mkmapnames(base string, ptr string) mapnames {
 	return mapnames{base, base + "_fast32", base + "_fast32" + ptr, base + "_fast64", base + "_fast64" + ptr, base + "_faststr"}
 }
 
-var mapaccess1 = mkmapnames("mapaccess1", "")
-var mapaccess2 = mkmapnames("mapaccess2", "")
+var mapaccess = mkmapnames("mapaccess2", "")
 var mapassign = mkmapnames("mapassign", "ptr")
 var mapdelete = mkmapnames("mapdelete", "")