cmd/compile: fuse escape analysis parameter tagging loops

Simplifies the code somewhat and allows removing Param.Field.

Passes toolstash-check.

Change-Id: Id854416aea8afd27ce4830ff0f5ff940f7353792
Reviewed-on: https://go-review.googlesource.com/99336
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -668,11 +668,6 @@ func tofunargs(l []*Node, funarg types.Funarg) *types.Type {
 	for i, n := range l {
 		f := structfield(n)
 		f.Funarg = funarg
-
-		// esc.go needs to find f given a PPARAM to add the tag.
-		if n.Left != nil && n.Left.Class() == PPARAM {
-			n.Left.Name.Param.Field = f
-		}
 		if f.Broke() {
 			t.SetBroke(true)
 		}
@@ -688,11 +683,6 @@ func tofunargsfield(fields []*types.Field, funarg types.Funarg) *types.Type {
 
 	for _, f := range fields {
 		f.Funarg = funarg
-
-		// esc.go needs to find f given a PPARAM to add the tag.
-		if asNode(f.Nname) != nil && asNode(f.Nname).Class() == PPARAM {
-			asNode(f.Nname).Name.Param.Field = f
-		}
 	}
 	t.SetFields(fields)
 	return t

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

@@ -2238,27 +2238,6 @@ func (e *EscState) esctag(fn *Node) {
 		}
 	}
 
-	for _, ln := range fn.Func.Dcl {
-		if ln.Op != ONAME {
-			continue
-		}
-
-		switch ln.Esc & EscMask {
-		case EscNone, // not touched by escflood
-			EscReturn:
-			if types.Haspointers(ln.Type) { // don't bother tagging for scalars
-				if ln.Name.Param.Field.Note != uintptrEscapesTag {
-					ln.Name.Param.Field.Note = mktag(int(ln.Esc))
-				}
-			}
-
-		case EscHeap: // touched by escflood, moved to heap
-		}
-	}
-
-	// Unnamed parameters are unused and therefore do not escape.
-	// (Unnamed parameters are not in the Dcl list in the loop above
-	// so we need to mark them separately.)
 	for _, fs := range types.RecvsParams {
 		for _, f := range fs(fn.Type).Fields().Slice() {
 			if !types.Haspointers(f.Type) { // don't bother tagging for scalars
@@ -2268,8 +2247,19 @@ func (e *EscState) esctag(fn *Node) {
 				// Note is already set in the loop above.
 				continue
 			}
+
+			// Unnamed parameters are unused and therefore do not escape.
 			if f.Sym == nil || f.Sym.IsBlank() {
 				f.Note = mktag(EscNone)
+				continue
+			}
+
+			switch esc := asNode(f.Nname).Esc; esc & EscMask {
+			case EscNone, // not touched by escflood
+				EscReturn:
+				f.Note = mktag(int(esc))
+
+			case EscHeap: // touched by escflood, moved to heap
 			}
 		}
 	}

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

@@ -24,7 +24,7 @@ func TestSizeof(t *testing.T) {
 	}{
 		{Func{}, 128, 232},
 		{Name{}, 32, 56},
-		{Param{}, 28, 56},
+		{Param{}, 24, 48},
 		{Node{}, 76, 128},
 	}
 

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

@@ -279,9 +279,6 @@ type Param struct {
 	// ONAME PAUTOHEAP
 	Stackcopy *Node // the PPARAM/PPARAMOUT on-stack slot (moved func params only)
 
-	// ONAME PPARAM
-	Field *types.Field // TFIELD in arg struct
-
 	// ONAME closure linkage
 	// Consider:
 	//