cmd/go: support -trimpath with gccgo

Fixes #32162

Change-Id: I164665108fa8ae299229054bded82cb3b027bccb
Reviewed-on: https://go-review.googlesource.com/c/go/+/196023
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/work/gccgo.go

@@ -91,6 +91,10 @@ func (tools gccgoToolchain) gc(b *Builder, a *Action, archive string, importcfg
 			args = append(args, "-I", root)
 		}
 	}
+	if cfg.BuildTrimpath && b.gccSupportsFlag(args[:1], "-ffile-prefix-map=a=b") {
+		args = append(args, "-ffile-prefix-map="+base.Cwd+"=.")
+		args = append(args, "-ffile-prefix-map="+b.WorkDir+"=/tmp/go-build")
+	}
 	args = append(args, a.Package.Internal.Gccgoflags...)
 	for _, f := range gofiles {
 		args = append(args, mkAbs(p.Dir, f))
@@ -535,7 +539,10 @@ func (tools gccgoToolchain) cc(b *Builder, a *Action, ofile, cfile string) error
 		defs = append(defs, "-fsplit-stack")
 	}
 	defs = tools.maybePIC(defs)
-	if b.gccSupportsFlag(compiler, "-fdebug-prefix-map=a=b") {
+	if b.gccSupportsFlag(compiler, "-ffile-prefix-map=a=b") {
+		defs = append(defs, "-ffile-prefix-map="+base.Cwd+"=.")
+		defs = append(defs, "-ffile-prefix-map="+b.WorkDir+"=/tmp/go-build")
+	} else if b.gccSupportsFlag(compiler, "-fdebug-prefix-map=a=b") {
 		defs = append(defs, "-fdebug-prefix-map="+b.WorkDir+"=/tmp/go-build")
 	}
 	if b.gccSupportsFlag(compiler, "-gno-record-gcc-switches") {

src/cmd/go/testdata/script/build_trimpath.txt

@@ -16,10 +16,10 @@ grep -q $GOROOT_REGEXP hello.exe
 go build -trimpath -o hello.exe hello.go
 ! grep -q $GOROOT_REGEXP hello.exe
 ! grep -q $WORK_REGEXP hello.exe
-cd ..
 
 # A binary from an external module built with -trimpath should not contain
 # the current workspace or GOROOT.
+cd $WORK
 env GO111MODULE=on
 go build -trimpath -o fortune.exe rsc.io/fortune
 ! grep -q $GOROOT_REGEXP fortune.exe
@@ -27,18 +27,35 @@ go build -trimpath -o fortune.exe rsc.io/fortune
 
 # Two binaries built from identical packages in different directories
 # should be identical.
-mkdir b
-cp a/go.mod a/hello.go b
-cd a
-go build -trimpath -o ../a.exe .
-cd ../b
-go build -trimpath -o ../b.exe .
-cd ..
-cmp -q a.exe b.exe
+cd $GOPATH/src/a
+go build -trimpath -o $WORK/a-GOPATH.exe .
+cd $WORK/_alt/src/a
+go build -trimpath -o $WORK/a-alt.exe .
+cmp -q $WORK/a-GOPATH.exe $WORK/a-alt.exe
+
+[!exec:gccgo] stop
+
+# Binaries built using gccgo should also be identical to each other.
+env GO111MODULE=off # The current released gccgo does not support builds in module mode.
+cd $GOPATH/src/a
+go build -compiler=gccgo -trimpath -o $WORK/gccgo-GOPATH.exe .
+
+env old_gopath=$GOPATH
+env GOPATH=$WORK/_alt
+cd $WORK/_alt/src/a
+go build -compiler=gccgo -trimpath -o $WORK/gccgo-alt.exe .
+cd $WORK
+! grep -q $GOROOT_REGEXP gccgo-GOPATH.exe
+! grep -q $WORK_REGEXP gccgo-GOPATH.exe
+cmp -q gccgo-GOPATH.exe gccgo-alt.exe
 
+-- $GOPATH/src/a/hello.go --
 package main
 func main() { println("hello") }
-func main() { println("hello") }
-
--- a/go.mod --
+-- $GOPATH/src/a/go.mod --
+module example.com/a
+-- $WORK/_alt/src/a/hello.go --
+package main
+func main() { println("hello") }
+-- $WORK/_alt/src/a/go.mod --
+module example.com/a