[dev.regabi] cmd/compile: add register ABI analysis utilities

Introduce a new utility routine for analyzing a given function
signature to how its various input and output parameters will be
passed (in registers or on the stack) for a given ABI description,
along with some unit tests.

Change-Id: Id64a98a0a142e42dd9c2dc9f6607c0d827ef84fb
Reviewed-on: https://go-review.googlesource.com/c/go/+/273011
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Trust: Than McIntosh <thanm@google.com>

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

@@ -0,0 +1,157 @@
+// Copyright 2020 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 gc
+
+// This file contains utility routines and harness infrastructure used
+// by the ABI tests in "abiutils_test.go".
+
+import (
+	"cmd/compile/internal/ir"
+	"cmd/compile/internal/types"
+	"cmd/internal/src"
+	"fmt"
+	"strings"
+	"testing"
+	"text/scanner"
+)
+
+func mkParamResultField(t *types.Type, s *types.Sym, which ir.Class) *types.Field {
+	field := types.NewField(src.NoXPos, s, t)
+	n := NewName(s)
+	n.SetClass(which)
+	field.Nname = n
+	n.SetType(t)
+	return field
+}
+
+// mkstruct is a helper routine to create a struct type with fields
+// of the types specified in 'fieldtypes'.
+func mkstruct(fieldtypes []*types.Type) *types.Type {
+	fields := make([]*types.Field, len(fieldtypes))
+	for k, t := range fieldtypes {
+		if t == nil {
+			panic("bad -- field has no type")
+		}
+		f := types.NewField(src.NoXPos, nil, t)
+		fields[k] = f
+	}
+	s := types.NewStruct(types.LocalPkg, fields)
+	return s
+}
+
+func mkFuncType(rcvr *types.Type, ins []*types.Type, outs []*types.Type) *types.Type {
+	q := lookup("?")
+	inf := []*types.Field{}
+	for _, it := range ins {
+		inf = append(inf, mkParamResultField(it, q, ir.PPARAM))
+	}
+	outf := []*types.Field{}
+	for _, ot := range outs {
+		outf = append(outf, mkParamResultField(ot, q, ir.PPARAMOUT))
+	}
+	var rf *types.Field
+	if rcvr != nil {
+		rf = mkParamResultField(rcvr, q, ir.PPARAM)
+	}
+	return types.NewSignature(types.LocalPkg, rf, inf, outf)
+}
+
+type expectedDump struct {
+	dump string
+	file string
+	line int
+}
+
+func tokenize(src string) []string {
+	var s scanner.Scanner
+	s.Init(strings.NewReader(src))
+	res := []string{}
+	for tok := s.Scan(); tok != scanner.EOF; tok = s.Scan() {
+		res = append(res, s.TokenText())
+	}
+	return res
+}
+
+func verifyParamResultOffset(t *testing.T, f *types.Field, r ABIParamAssignment, which string, idx int) int {
+	n := ir.AsNode(f.Nname)
+	if n == nil {
+		panic("not expected")
+	}
+	if n.Offset() != int64(r.Offset) {
+		t.Errorf("%s %d: got offset %d wanted %d t=%v",
+			which, idx, r.Offset, n.Offset(), f.Type)
+		return 1
+	}
+	return 0
+}
+
+func makeExpectedDump(e string) expectedDump {
+	return expectedDump{dump: e}
+}
+
+func difftokens(atoks []string, etoks []string) string {
+	if len(atoks) != len(etoks) {
+		return fmt.Sprintf("expected %d tokens got %d",
+			len(etoks), len(atoks))
+	}
+	for i := 0; i < len(etoks); i++ {
+		if etoks[i] == atoks[i] {
+			continue
+		}
+
+		return fmt.Sprintf("diff at token %d: expected %q got %q",
+			i, etoks[i], atoks[i])
+	}
+	return ""
+}
+
+func abitest(t *testing.T, ft *types.Type, exp expectedDump) {
+
+	dowidth(ft)
+
+	// Analyze with full set of registers.
+	regRes := ABIAnalyze(ft, configAMD64)
+	regResString := strings.TrimSpace(regRes.String())
+
+	// Check results.
+	reason := difftokens(tokenize(regResString), tokenize(exp.dump))
+	if reason != "" {
+		t.Errorf("\nexpected:\n%s\ngot:\n%s\nreason: %s",
+			strings.TrimSpace(exp.dump), regResString, reason)
+	}
+
+	// Analyze again with empty register set.
+	empty := ABIConfig{}
+	emptyRes := ABIAnalyze(ft, empty)
+	emptyResString := emptyRes.String()
+
+	// Walk the results and make sure the offsets assigned match
+	// up with those assiged by dowidth. This checks to make sure that
+	// when we have no available registers the ABI assignment degenerates
+	// back to the original ABI0.
+
+	// receiver
+	failed := 0
+	rfsl := ft.Recvs().Fields().Slice()
+	poff := 0
+	if len(rfsl) != 0 {
+		failed |= verifyParamResultOffset(t, rfsl[0], emptyRes.inparams[0], "receiver", 0)
+		poff = 1
+	}
+	// params
+	pfsl := ft.Params().Fields().Slice()
+	for k, f := range pfsl {
+		verifyParamResultOffset(t, f, emptyRes.inparams[k+poff], "param", k)
+	}
+	// results
+	ofsl := ft.Results().Fields().Slice()
+	for k, f := range ofsl {
+		failed |= verifyParamResultOffset(t, f, emptyRes.outparams[k], "result", k)
+	}
+
+	if failed != 0 {
+		t.Logf("emptyres:\n%s\n", emptyResString)
+	}
+}