cmd/compile: apply FixVariadicCall and FixMethodCall during typecheck

To simplify backend analysis, we normalize variadic and method calls:
variadic calls are rewritten with an explicit slice argument, and
method calls are turned into function calls that pass the receiver
argument as the first parameter.

But because we've been supporting multiple frontends, this
normalization was scattered in various later passes. Now that we're
back to just one frontend, we can move the normalization forward into
typecheck (where most other IR normalization already happens).

Change-Id: Idd05ae231fc180ae3dd1664452414f6b6d578962
Reviewed-on: https://go-review.googlesource.com/c/go/+/463737
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/escape/call.go

@@ -45,8 +45,7 @@ func (e *escape) callCommon(ks []hole, call ir.Node, init *ir.Nodes, wrapper *ir
 
 	case ir.OCALLFUNC, ir.OCALLMETH, ir.OCALLINTER:
 		call := call.(*ir.CallExpr)
-		typecheck.FixVariadicCall(call)
+		typecheck.AssertFixedCall(call)
-		typecheck.FixMethodCall(call)
 
 		// Pick out the function callee, if statically known.
 		//

src/cmd/compile/internal/inline/inl.go

@@ -981,7 +981,7 @@ func mkinlcall(n *ir.CallExpr, fn *ir.Func, maxCost int32, inlCalls *[]*ir.Inlin
 		}
 	}
 
-	typecheck.FixVariadicCall(n)
+	typecheck.AssertFixedCall(n)
 
 	inlIndex := base.Ctxt.InlTree.Add(parent, n.Pos(), sym)
 

src/cmd/compile/internal/typecheck/func.go

@@ -76,6 +76,15 @@ func FixMethodCall(call *ir.CallExpr) {
 	call.Args = args
 }
 
+func AssertFixedCall(call *ir.CallExpr) {
+	if call.X.Type().IsVariadic() && !call.IsDDD {
+		base.FatalfAt(call.Pos(), "missed FixVariadicCall")
+	}
+	if call.Op() == ir.OCALLMETH {
+		base.FatalfAt(call.Pos(), "missed FixMethodCall")
+	}
+}
+
 // ClosureType returns the struct type used to hold all the information
 // needed in the closure for clo (clo must be a OCLOSURE node).
 // The address of a variable of the returned type can be cast to a func.
@@ -339,6 +348,7 @@ func tcCall(n *ir.CallExpr, top int) ir.Node {
 	}
 
 	typecheckaste(ir.OCALL, n.X, n.IsDDD, t.Params(), n.Args, func() string { return fmt.Sprintf("argument to %v", n.X) })
+	FixVariadicCall(n)
 	FixMethodCall(n)
 	if t.NumResults() == 0 {
 		return n

src/cmd/compile/internal/walk/order.go

@@ -536,7 +536,7 @@ func (o *orderState) call(nn ir.Node) {
 	}
 
 	n := nn.(*ir.CallExpr)
-	typecheck.FixVariadicCall(n)
+	typecheck.AssertFixedCall(n)
 
 	if isFuncPCIntrinsic(n) && isIfaceOfFunc(n.Args[0]) {
 		// For internal/abi.FuncPCABIxxx(fn), if fn is a defined function,