[dev.typeparams] cmd/compile: add types2-based noder

This CL adds "irgen", a new noding implementation that utilizes types2
to guide IR construction. Notably, it completely skips dealing with
constant and type expressions (aside from using ir.TypeNode to
interoperate with the types1 typechecker), because types2 already
handled those. It also omits any syntax checking, trusting that types2
already rejected any errors.

It currently still utilizes the types1 typechecker for the desugaring
operations it handles (e.g., turning OAS2 into OAS2FUNC/etc, inserting
implicit conversions, rewriting f(g()) functions, and so on). However,
the IR is constructed in a fully incremental fashion, so it should be
easy to now piecemeal replace those dependencies as needed.

Nearly all of "go test std cmd" passes with -G=3 enabled by
default. The main remaining blocker is the number of test/run.go
failures. There also appear to be cases where types2 does not provide
us with position information. These will be iterated upon.

Portions and ideas from Dan Scales's CL 276653.

Change-Id: Ic99e8f2d0267b0312d30c10d5d043f5817a59c9d
Reviewed-on: https://go-review.googlesource.com/c/go/+/281932
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>

1 files changed, 169 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/object.go b/src/cmd/compile/internal/noder/object.go
new file mode 100644
index 0000000000..9567042156
--- /dev/null
+++ b/src/cmd/compile/internal/noder/object.go
@@ -0,0 +1,169 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/syntax"
+	"cmd/compile/internal/typecheck"
+	"cmd/compile/internal/types"
+	"cmd/compile/internal/types2"
+	"cmd/internal/src"
+)
+
+func (g *irgen) def(name *syntax.Name) (*ir.Name, types2.Object) {
+	obj, ok := g.info.Defs[name]
+	if !ok {
+		base.FatalfAt(g.pos(name), "unknown name %v", name)
+	}
+	return g.obj(obj), obj
+}
+
+func (g *irgen) use(name *syntax.Name) *ir.Name {
+	obj, ok := g.info.Uses[name]
+	if !ok {
+		base.FatalfAt(g.pos(name), "unknown name %v", name)
+	}
+	return ir.CaptureName(g.pos(obj), ir.CurFunc, g.obj(obj))
+}
+
+// obj returns the Name that represents the given object. If no such
+// Name exists yet, it will be implicitly created.
+//
+// For objects declared at function scope, ir.CurFunc must already be
+// set to the respective function when the Name is created.
+func (g *irgen) obj(obj types2.Object) *ir.Name {
+	// For imported objects, we use iimport directly instead of mapping
+	// the types2 representation.
+	if obj.Pkg() != g.self {
+		sym := g.sym(obj)
+		if sym.Def != nil {
+			return sym.Def.(*ir.Name)
+		}
+		n := typecheck.Resolve(ir.NewIdent(src.NoXPos, sym))
+		if n, ok := n.(*ir.Name); ok {
+			return n
+		}
+		base.FatalfAt(g.pos(obj), "failed to resolve %v", obj)
+	}
+
+	if name, ok := g.objs[obj]; ok {
+		return name // previously mapped
+	}
+
+	var name *ir.Name
+	pos := g.pos(obj)
+
+	class := typecheck.DeclContext
+	if obj.Parent() == g.self.Scope() {
+		class = ir.PEXTERN // forward reference to package-block declaration
+	}
+
+	// "You are in a maze of twisting little passages, all different."
+	switch obj := obj.(type) {
+	case *types2.Const:
+		name = g.objCommon(pos, ir.OLITERAL, g.sym(obj), class, g.typ(obj.Type()))
+
+	case *types2.Func:
+		sig := obj.Type().(*types2.Signature)
+		var sym *types.Sym
+		var typ *types.Type
+		if recv := sig.Recv(); recv == nil {
+			if obj.Name() == "init" {
+				sym = renameinit()
+			} else {
+				sym = g.sym(obj)
+			}
+			typ = g.typ(sig)
+		} else {
+			sym = ir.MethodSym(g.typ(recv.Type()), g.selector(obj))
+			typ = g.signature(g.param(recv), sig)
+		}
+		name = g.objCommon(pos, ir.ONAME, sym, ir.PFUNC, typ)
+
+	case *types2.TypeName:
+		if obj.IsAlias() {
+			name = g.objCommon(pos, ir.OTYPE, g.sym(obj), class, g.typ(obj.Type()))
+		} else {
+			name = ir.NewDeclNameAt(pos, ir.OTYPE, g.sym(obj))
+			g.objFinish(name, class, types.NewNamed(name))
+		}
+
+	case *types2.Var:
+		var sym *types.Sym
+		if class == ir.PPARAMOUT {
+			// Backend needs names for result parameters,
+			// even if they're anonymous or blank.
+			switch obj.Name() {
+			case "":
+				sym = typecheck.LookupNum("~r", len(ir.CurFunc.Dcl)) // 'r' for "result"
+			case "_":
+				sym = typecheck.LookupNum("~b", len(ir.CurFunc.Dcl)) // 'b' for "blank"
+			}
+		}
+		if sym == nil {
+			sym = g.sym(obj)
+		}
+		name = g.objCommon(pos, ir.ONAME, sym, class, g.typ(obj.Type()))
+
+	default:
+		g.unhandled("object", obj)
+	}
+
+	g.objs[obj] = name
+	return name
+}
+
+func (g *irgen) objCommon(pos src.XPos, op ir.Op, sym *types.Sym, class ir.Class, typ *types.Type) *ir.Name {
+	name := ir.NewDeclNameAt(pos, op, sym)
+	g.objFinish(name, class, typ)
+	return name
+}
+
+func (g *irgen) objFinish(name *ir.Name, class ir.Class, typ *types.Type) {
+	sym := name.Sym()
+
+	name.SetType(typ)
+	name.Class = class
+	if name.Class == ir.PFUNC {
+		sym.SetFunc(true)
+	}
+
+	// We already know name's type, but typecheck is really eager to try
+	// recomputing it later. This appears to prevent that at least.
+	name.Ntype = ir.TypeNode(typ)
+	name.SetTypecheck(1)
+	name.SetWalkdef(1)
+
+	if ir.IsBlank(name) {
+		return
+	}
+
+	switch class {
+	case ir.PEXTERN:
+		g.target.Externs = append(g.target.Externs, name)
+		fallthrough
+	case ir.PFUNC:
+		sym.Def = name
+		if name.Class == ir.PFUNC && name.Type().Recv() != nil {
+			break // methods are exported with their receiver type
+		}
+		if types.IsExported(sym.Name) {
+			typecheck.Export(name)
+		}
+		if base.Flag.AsmHdr != "" && !name.Sym().Asm() {
+			name.Sym().SetAsm(true)
+			g.target.Asms = append(g.target.Asms, name)
+		}
+
+	default:
+		// Function-scoped declaration.
+		name.Curfn = ir.CurFunc
+		if name.Op() == ir.ONAME {
+			ir.CurFunc.Dcl = append(ir.CurFunc.Dcl, name)
+		}
+	}
+}