[dev.regabi] cmd/compile: backport changes from dev.typeparams (9456804)

This CL backports a bunch of changes that landed on dev.typeparams,
but are not dependent on types2 or generics. By backporting, we reduce
the divergence between development branches, hopefully improving test
coverage and reducing risk of merge conflicts.

Updates #43866.

Change-Id: I382510855c9b5fac52b17066e44a00bd07fe86f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/286172
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 83 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/posmap.go b/src/cmd/compile/internal/noder/posmap.go
new file mode 100644
index 0000000000..a6d3e2d7ef
--- /dev/null
+++ b/src/cmd/compile/internal/noder/posmap.go
@@ -0,0 +1,83 @@
+// 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/syntax"
+	"cmd/internal/src"
+)
+
+// A posMap handles mapping from syntax.Pos to src.XPos.
+type posMap struct {
+	bases map[*syntax.PosBase]*src.PosBase
+	cache struct {
+		last *syntax.PosBase
+		base *src.PosBase
+	}
+}
+
+type poser interface{ Pos() syntax.Pos }
+type ender interface{ End() syntax.Pos }
+
+func (m *posMap) pos(p poser) src.XPos { return m.makeXPos(p.Pos()) }
+func (m *posMap) end(p ender) src.XPos { return m.makeXPos(p.End()) }
+
+func (m *posMap) makeXPos(pos syntax.Pos) src.XPos {
+	if !pos.IsKnown() {
+		// TODO(mdempsky): Investigate restoring base.Fatalf.
+		return src.NoXPos
+	}
+
+	posBase := m.makeSrcPosBase(pos.Base())
+	return base.Ctxt.PosTable.XPos(src.MakePos(posBase, pos.Line(), pos.Col()))
+}
+
+// makeSrcPosBase translates from a *syntax.PosBase to a *src.PosBase.
+func (m *posMap) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
+	// fast path: most likely PosBase hasn't changed
+	if m.cache.last == b0 {
+		return m.cache.base
+	}
+
+	b1, ok := m.bases[b0]
+	if !ok {
+		fn := b0.Filename()
+		if b0.IsFileBase() {
+			b1 = src.NewFileBase(fn, absFilename(fn))
+		} else {
+			// line directive base
+			p0 := b0.Pos()
+			p0b := p0.Base()
+			if p0b == b0 {
+				panic("infinite recursion in makeSrcPosBase")
+			}
+			p1 := src.MakePos(m.makeSrcPosBase(p0b), p0.Line(), p0.Col())
+			b1 = src.NewLinePragmaBase(p1, fn, fileh(fn), b0.Line(), b0.Col())
+		}
+		if m.bases == nil {
+			m.bases = make(map[*syntax.PosBase]*src.PosBase)
+		}
+		m.bases[b0] = b1
+	}
+
+	// update cache
+	m.cache.last = b0
+	m.cache.base = b1
+
+	return b1
+}
+
+func (m *posMap) join(other *posMap) {
+	if m.bases == nil {
+		m.bases = make(map[*syntax.PosBase]*src.PosBase)
+	}
+	for k, v := range other.bases {
+		if m.bases[k] != nil {
+			base.Fatalf("duplicate posmap bases")
+		}
+		m.bases[k] = v
+	}
+}