diff --git a/src/cmd/compile/internal/importer/iimport.go b/src/cmd/compile/internal/importer/iimport.go
index ac5ec7c8f29..4384e59c30a 100644
--- a/src/cmd/compile/internal/importer/iimport.go
+++ b/src/cmd/compile/internal/importer/iimport.go
@@ -257,7 +257,7 @@ func (p *iimporter) posBaseAt(off uint64) *syntax.PosBase {
 		return posBase
 	}
 	filename := p.stringAt(off)
-	posBase := syntax.NewFileBase(filename)
+	posBase := syntax.NewTrimmedFileBase(filename, true)
 	p.posBaseCache[off] = posBase
 	return posBase
 }
diff --git a/src/cmd/compile/internal/noder/noder.go b/src/cmd/compile/internal/noder/noder.go
index 6a2aacd3fea..2b67a91b3f7 100644
--- a/src/cmd/compile/internal/noder/noder.go
+++ b/src/cmd/compile/internal/noder/noder.go
@@ -191,13 +191,23 @@ func (p *noder) errorAt(pos syntax.Pos, format string, args ...interface{}) {
 	base.ErrorfAt(p.makeXPos(pos), format, args...)
 }
 
-// TODO(gri) Can we eliminate fileh in favor of absFilename?
-func fileh(name string) string {
-	return objabi.AbsFile("", name, base.Flag.TrimPath)
-}
-
-func absFilename(name string) string {
-	return objabi.AbsFile(base.Ctxt.Pathname, name, base.Flag.TrimPath)
+// trimFilename returns the "trimmed" filename of b, which is the
+// absolute filename after applying -trimpath processing. This
+// filename form is suitable for use in object files and export data.
+//
+// If b's filename has already been trimmed (i.e., because it was read
+// in from an imported package's export data), then the filename is
+// returned unchanged.
+func trimFilename(b *syntax.PosBase) string {
+	filename := b.Filename()
+	if !b.Trimmed() {
+		dir := ""
+		if b.IsFileBase() {
+			dir = base.Ctxt.Pathname
+		}
+		filename = objabi.AbsFile(dir, filename, base.Flag.TrimPath)
+	}
+	return filename
 }
 
 // noder transforms package syntax's AST into a Node tree.
@@ -1723,7 +1733,7 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 // (primarily misuse of linker flags), other files are not.
 // See golang.org/issue/23672.
 func isCgoGeneratedFile(pos syntax.Pos) bool {
-	return strings.HasPrefix(filepath.Base(filepath.Clean(fileh(pos.Base().Filename()))), "_cgo_")
+	return strings.HasPrefix(filepath.Base(trimFilename(pos.Base())), "_cgo_")
 }
 
 // safeArg reports whether arg is a "safe" command-line argument,
diff --git a/src/cmd/compile/internal/noder/posmap.go b/src/cmd/compile/internal/noder/posmap.go
index a6d3e2d7ef4..f22628f845f 100644
--- a/src/cmd/compile/internal/noder/posmap.go
+++ b/src/cmd/compile/internal/noder/posmap.go
@@ -45,8 +45,10 @@ func (m *posMap) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
 	b1, ok := m.bases[b0]
 	if !ok {
 		fn := b0.Filename()
+		absfn := trimFilename(b0)
+
 		if b0.IsFileBase() {
-			b1 = src.NewFileBase(fn, absFilename(fn))
+			b1 = src.NewFileBase(fn, absfn)
 		} else {
 			// line directive base
 			p0 := b0.Pos()
@@ -55,7 +57,7 @@ func (m *posMap) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
 				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())
+			b1 = src.NewLinePragmaBase(p1, fn, absfn, b0.Line(), b0.Col())
 		}
 		if m.bases == nil {
 			m.bases = make(map[*syntax.PosBase]*src.PosBase)
diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 5481812b18d..985453a1bb3 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -194,16 +194,15 @@ func (pr *pkgReader) posBaseIdx(idx int) *src.PosBase {
 	r := pr.newReader(relocPosBase, idx, syncPosBase)
 	var b *src.PosBase
 
-	fn := r.string()
-	absfn := r.string()
+	filename := r.string()
 
 	if r.bool() {
-		b = src.NewFileBase(fn, absfn)
+		b = src.NewFileBase(filename, filename)
 	} else {
 		pos := r.pos0()
 		line := r.uint()
 		col := r.uint()
-		b = src.NewLinePragmaBase(pos, fn, absfn, line, col)
+		b = src.NewLinePragmaBase(pos, filename, filename, line, col)
 	}
 
 	pr.posBases[idx] = b
diff --git a/src/cmd/compile/internal/noder/reader2.go b/src/cmd/compile/internal/noder/reader2.go
index 22c742ab251..64c1612f706 100644
--- a/src/cmd/compile/internal/noder/reader2.go
+++ b/src/cmd/compile/internal/noder/reader2.go
@@ -109,15 +109,14 @@ func (pr *pkgReader2) posBaseIdx(idx int) *syntax.PosBase {
 	var b *syntax.PosBase
 
 	filename := r.string()
-	_ = r.string() // absolute file name
 
 	if r.bool() {
-		b = syntax.NewFileBase(filename)
+		b = syntax.NewTrimmedFileBase(filename, true)
 	} else {
 		pos := r.pos()
 		line := r.uint()
 		col := r.uint()
-		b = syntax.NewLineBase(pos, filename, line, col)
+		b = syntax.NewLineBase(pos, filename, true, line, col)
 	}
 
 	pr.posBases[idx] = b
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index d971bd0d164..a33b24e50cb 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -189,11 +189,7 @@ func (pw *pkgWriter) posBaseIdx(b *syntax.PosBase) int {
 	w := pw.newWriter(relocPosBase, syncPosBase)
 	w.p.posBasesIdx[b] = w.idx
 
-	// TODO(mdempsky): What exactly does "fileh" do anyway? Is writing
-	// out both of these strings really the right thing to do here?
-	fn := b.Filename()
-	w.string(fn)
-	w.string(fileh(fn))
+	w.string(trimFilename(b))
 
 	if !w.bool(b.IsFileBase()) {
 		w.pos(b)
diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 4fb6de10a82..c477ddd45d5 100644
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -146,11 +146,13 @@ func (p *parser) updateBase(pos Pos, tline, tcol uint, text string) {
 	// If we have a column (//line filename:line:col form),
 	// an empty filename means to use the previous filename.
 	filename := text[:i-1] // lop off ":line"
+	trimmed := false
 	if filename == "" && ok2 {
 		filename = p.base.Filename()
+		trimmed = p.base.Trimmed()
 	}
 
-	p.base = NewLineBase(pos, filename, line, col)
+	p.base = NewLineBase(pos, filename, trimmed, line, col)
 }
 
 func commentText(s string) string {
diff --git a/src/cmd/compile/internal/syntax/pos.go b/src/cmd/compile/internal/syntax/pos.go
index baebcc995c7..1494c0989fb 100644
--- a/src/cmd/compile/internal/syntax/pos.go
+++ b/src/cmd/compile/internal/syntax/pos.go
@@ -133,13 +133,19 @@ type PosBase struct {
 	pos       Pos
 	filename  string
 	line, col uint32
+	trimmed   bool // whether -trimpath has been applied
 }
 
 // NewFileBase returns a new PosBase for the given filename.
 // A file PosBase's position is relative to itself, with the
 // position being filename:1:1.
 func NewFileBase(filename string) *PosBase {
-	base := &PosBase{MakePos(nil, linebase, colbase), filename, linebase, colbase}
+	return NewTrimmedFileBase(filename, false)
+}
+
+// NewTrimmedFileBase is like NewFileBase, but allows specifying Trimmed.
+func NewTrimmedFileBase(filename string, trimmed bool) *PosBase {
+	base := &PosBase{MakePos(nil, linebase, colbase), filename, linebase, colbase, trimmed}
 	base.pos.base = base
 	return base
 }
@@ -149,8 +155,8 @@ func NewFileBase(filename string) *PosBase {
 // the comment containing the line directive. For a directive in a line comment,
 // that position is the beginning of the next line (i.e., the newline character
 // belongs to the line comment).
-func NewLineBase(pos Pos, filename string, line, col uint) *PosBase {
-	return &PosBase{pos, filename, sat32(line), sat32(col)}
+func NewLineBase(pos Pos, filename string, trimmed bool, line, col uint) *PosBase {
+	return &PosBase{pos, filename, sat32(line), sat32(col), trimmed}
 }
 
 func (base *PosBase) IsFileBase() bool {
@@ -188,6 +194,13 @@ func (base *PosBase) Col() uint {
 	return uint(base.col)
 }
 
+func (base *PosBase) Trimmed() bool {
+	if base == nil {
+		return false
+	}
+	return base.trimmed
+}
+
 func sat32(x uint) uint32 {
 	if x > PosMax {
 		return PosMax