cmd/compile: revert most of CL 349169

The method of using references to dictionaries to hold methods
live during linker deadcode elimination wasn't working very well.
I implemented a new scheme in the CL below this, so this CL strips
out the old method.

The new method has the added benefit of having 0 runtime overhead
(unlike the stuff we're ripping out here, which does have a small overhead).

Update #48047

Change-Id: I68ac57119792d53c58f1480f407de6ab2bb53211
Reviewed-on: https://go-review.googlesource.com/c/go/+/357836
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

src/cmd/compile/internal/noder/helpers.go

@@ -183,7 +183,7 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 	// If no type params, do the normal call transformations. This
 	// will convert OCALL to OCALLFUNC.
 	typed(typ, n)
-	transformCall(n, nil)
+	transformCall(n)
 	return n
 }
 

src/cmd/compile/internal/noder/stencil.go

@@ -185,7 +185,7 @@ func (g *genInst) scanForGenCalls(decl ir.Node) {
 			// it before installing the instantiation, so we are
 			// checking against non-shape param types in
 			// typecheckaste.
-			transformCall(call, nil)
+			transformCall(call)
 
 			// Replace the OFUNCINST with a direct reference to the
 			// new stenciled function
@@ -223,7 +223,7 @@ func (g *genInst) scanForGenCalls(decl ir.Node) {
 
 			// Transform the Call now, which changes OCALL
 			// to OCALLFUNC and does typecheckaste/assignconvfn.
-			transformCall(call, nil)
+			transformCall(call)
 
 			st := g.getInstantiation(gf, targs, true).fun
 			dictValue, usingSubdict := g.getDictOrSubdict(declInfo, n, gf, targs, true)
@@ -1089,14 +1089,14 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				// transform the call.
 				call.X.(*ir.SelectorExpr).SetOp(ir.OXDOT)
 				transformDot(call.X.(*ir.SelectorExpr), true)
-				transformCall(call, subst.info.dictParam)
+				transformCall(call)
 
 			case ir.ODOT, ir.ODOTPTR:
 				// An OXDOT for a generic receiver was resolved to
 				// an access to a field which has a function
 				// value. Transform the call to that function, now
 				// that the OXDOT was resolved.
-				transformCall(call, subst.info.dictParam)
+				transformCall(call)
 
 			case ir.ONAME:
 				name := call.X.Name()
@@ -1113,24 +1113,24 @@ func (subst *subster) node(n ir.Node) ir.Node {
 					// This is the case of a function value that was a
 					// type parameter (implied to be a function via a
 					// structural constraint) which is now resolved.
-					transformCall(call, subst.info.dictParam)
+					transformCall(call)
 				}
 
 			case ir.OCLOSURE:
-				transformCall(call, subst.info.dictParam)
+				transformCall(call)
 
 			case ir.ODEREF, ir.OINDEX, ir.OINDEXMAP, ir.ORECV:
 				// Transform a call that was delayed because of the
 				// use of typeparam inside an expression that required
 				// a pointer dereference, array indexing, map indexing,
 				// or channel receive to compute function value.
-				transformCall(call, subst.info.dictParam)
+				transformCall(call)
 
 			case ir.OCALL, ir.OCALLFUNC, ir.OCALLMETH, ir.OCALLINTER:
-				transformCall(call, subst.info.dictParam)
+				transformCall(call)
 
 			case ir.OCONVNOP:
-				transformCall(call, subst.info.dictParam)
+				transformCall(call)
 
 			case ir.OFUNCINST:
 				// A call with an OFUNCINST will get transformed
@@ -1276,7 +1276,7 @@ func (g *genInst) dictPass(info *instInfo) {
 					m.(*ir.CallExpr).X.(*ir.SelectorExpr).SetOp(ir.OXDOT)
 					transformDot(m.(*ir.CallExpr).X.(*ir.SelectorExpr), true)
 				}
-				transformCall(m.(*ir.CallExpr), info.dictParam)
+				transformCall(m.(*ir.CallExpr))
 			}
 
 		case ir.OCONVIFACE:

src/cmd/compile/internal/noder/transform.go

@@ -132,9 +132,7 @@ func transformConvCall(n *ir.CallExpr) ir.Node {
 // transformCall transforms a normal function/method call. Corresponds to last half
 // (non-conversion, non-builtin part) of typecheck.tcCall. This code should work even
 // in the case of OCALL/OFUNCINST.
-// The dict parameter is used for OCALLINTER nodes to ensure that the called method
-// is retained by the linker.
-func transformCall(n *ir.CallExpr, dict *ir.Name) {
+func transformCall(n *ir.CallExpr) {
 	// n.Type() can be nil for calls with no return value
 	assert(n.Typecheck() == 1)
 	transformArgs(n)
@@ -144,17 +142,6 @@ func transformCall(n *ir.CallExpr, dict *ir.Name) {
 	switch l.Op() {
 	case ir.ODOTINTER:
 		n.SetOp(ir.OCALLINTER)
-		if n.X.(*ir.SelectorExpr).X.Type().HasShape() {
-			if dict == nil {
-				base.Fatalf("calls on shape interfaces need a dictionary reference")
-			}
-			dict.SetAddrtaken(true)
-			// KeepAlive isn't exactly the right thing here, as we only
-			// need to keep the dictionary live in the linker-deadcode
-			// sense, not the at-runtime sense. But the at-runtime sense
-			// is stronger, so it works. See issue 48047.
-			n.KeepAlive = append(n.KeepAlive, dict)
-		}
 
 	case ir.ODOTMETH:
 		l := l.(*ir.SelectorExpr)