cmd/compile: eliminate fallback code for missing -p flag

cmd/compile has required the -p flag since go.dev/cl/391014. It's safe
to eliminate the fallback code that tried to cope without.

Change-Id: I9a62ff829e34a6fa5bfe6ae6a836610cc3f0cd33
Reviewed-on: https://go-review.googlesource.com/c/go/+/523337
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/dwarfgen/dwarf.go

@@ -524,9 +524,7 @@ func createComplexVar(fnsym *obj.LSym, fn *ir.Func, varID ssa.VarID) *dwarf.Var
 // in the DWARF info.
 func RecordFlags(flags ...string) {
 	if base.Ctxt.Pkgpath == "" {
-		// We can't record the flags if we don't know what the
-		// package name is.
-		return
+		panic("missing pkgpath")
 	}
 
 	type BoolFlag interface {

src/cmd/compile/internal/noder/import.go

@@ -133,7 +133,10 @@ func resolveImportPath(path string) (string, error) {
 		return "", errors.New("cannot import \"main\"")
 	}
 
-	if base.Ctxt.Pkgpath != "" && path == base.Ctxt.Pkgpath {
+	if base.Ctxt.Pkgpath == "" {
+		panic("missing pkgpath")
+	}
+	if path == base.Ctxt.Pkgpath {
 		return "", fmt.Errorf("import %q while compiling that package (import cycle)", path)
 	}
 

src/cmd/compile/internal/noder/noder.go

@@ -265,8 +265,7 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 			// user didn't provide one.
 			target = objabi.PathToPrefix(base.Ctxt.Pkgpath) + "." + f[1]
 		} else {
-			p.error(syntax.Error{Pos: pos, Msg: "//go:linkname requires linkname argument or -p compiler flag"})
-			break
+			panic("missing pkgpath")
 		}
 		p.linknames = append(p.linknames, linkname{pos, f[1], target})
 

src/cmd/compile/internal/reflectdata/reflect.go

@@ -432,13 +432,7 @@ func dgopkgpath(s *obj.LSym, ot int, pkg *types.Pkg) int {
 	}
 
 	if pkg == types.LocalPkg && base.Ctxt.Pkgpath == "" {
-		// If we don't know the full import path of the package being compiled
-		// (i.e. -p was not passed on the compiler command line), emit a reference to
-		// type:.importpath.""., which the linker will rewrite using the correct import path.
-		// Every package that imports this one directly defines the symbol.
-		// See also https://groups.google.com/forum/#!topic/golang-dev/myb9s53HxGQ.
-		ns := base.Ctxt.Lookup(`type:.importpath."".`)
-		return objw.SymPtr(s, ot, ns, 0)
+		panic("missing pkgpath")
 	}
 
 	dimportpath(pkg)
@@ -451,13 +445,7 @@ func dgopkgpathOff(s *obj.LSym, ot int, pkg *types.Pkg) int {
 		return objw.Uint32(s, ot, 0)
 	}
 	if pkg == types.LocalPkg && base.Ctxt.Pkgpath == "" {
-		// If we don't know the full import path of the package being compiled
-		// (i.e. -p was not passed on the compiler command line), emit a reference to
-		// type:.importpath.""., which the linker will rewrite using the correct import path.
-		// Every package that imports this one directly defines the symbol.
-		// See also https://groups.google.com/forum/#!topic/golang-dev/myb9s53HxGQ.
-		ns := base.Ctxt.Lookup(`type:.importpath."".`)
-		return objw.SymPtrOff(s, ot, ns)
+		panic("missing pkgpath")
 	}
 
 	dimportpath(pkg)
@@ -546,7 +534,9 @@ func dname(name, tag string, pkg *types.Pkg, exported, embedded bool) *obj.LSym
 			}
 		}
 	} else {
-		sname = fmt.Sprintf(`%s"".%d`, sname, dnameCount)
+		// TODO(mdempsky): We should be able to share these too (except
+		// maybe when dynamic linking).
+		sname = fmt.Sprintf("%s%s.%d", sname, types.LocalPkg.Prefix, dnameCount)
 		dnameCount++
 	}
 	if embedded {

src/cmd/compile/internal/types/size.go

@@ -195,8 +195,10 @@ func calcStructOffset(t *Type, fields []*Field, offset int64) int64 {
 }
 
 func isAtomicStdPkg(p *Pkg) bool {
-	return (p.Prefix == "sync/atomic" || p.Prefix == `""` && base.Ctxt.Pkgpath == "sync/atomic") ||
-		(p.Prefix == "runtime/internal/atomic" || p.Prefix == `""` && base.Ctxt.Pkgpath == "runtime/internal/atomic")
+	if p.Prefix == `""` {
+		panic("bad package prefix")
+	}
+	return p.Prefix == "sync/atomic" || p.Prefix == "runtime/internal/atomic"
 }
 
 // CalcSize calculates and stores the size and alignment for t.

src/cmd/compile/internal/walk/order.go

@@ -1507,7 +1507,7 @@ func isFuncPCIntrinsic(n *ir.CallExpr) bool {
 	}
 	fn := n.X.(*ir.Name).Sym()
 	return (fn.Name == "FuncPCABI0" || fn.Name == "FuncPCABIInternal") &&
-		(fn.Pkg.Path == "internal/abi" || fn.Pkg == types.LocalPkg && base.Ctxt.Pkgpath == "internal/abi")
+		fn.Pkg.Path == "internal/abi"
 }
 
 // isIfaceOfFunc returns whether n is an interface conversion from a direct reference of a func.