cmd/compile: fix irgen mis-handling invalid function declaration

In -G=3 mode, irgen use its own generated IR, which is mis-handling of
bodyless function and declared function with //go:noescape pragma.

Fix this by adopting the same logic in noder.funcDecl, which minor
change in linkname detection.

Fixes #48097

Change-Id: Ibef921c1f75e071ca61685e0cb4543f2ee5efc7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/346470
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dan Scales <danscales@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -113,6 +113,10 @@ func (g *irgen) funcDecl(out *ir.Nodes, decl *syntax.FuncDecl) {
 		}
 	}
 
+	if decl.Body != nil && fn.Pragma&ir.Noescape != 0 {
+		base.ErrorfAt(fn.Pos(), "can only use //go:noescape with external func implementations")
+	}
+
 	if decl.Name.Value == "init" && decl.Recv == nil {
 		g.target.Inits = append(g.target.Inits, fn)
 	}

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

@@ -272,12 +272,6 @@ Outer:
 		}
 	}
 
-	// Check for unusual case where noder2 encounters a type error that types2
-	// doesn't check for (e.g. notinheap incompatibility).
-	base.ExitIfErrors()
-
-	typecheck.DeclareUniverse()
-
 	for _, p := range noders {
 		// Process linkname and cgo pragmas.
 		p.processPragmas()
@@ -290,6 +284,22 @@ Outer:
 		})
 	}
 
+	if base.Flag.Complete {
+		for _, n := range g.target.Decls {
+			if fn, ok := n.(*ir.Func); ok {
+				if fn.Body == nil && fn.Nname.Sym().Linkname == "" {
+					base.ErrorfAt(fn.Pos(), "missing function body")
+				}
+			}
+		}
+	}
+
+	// Check for unusual case where noder2 encounters a type error that types2
+	// doesn't check for (e.g. notinheap incompatibility).
+	base.ExitIfErrors()
+
+	typecheck.DeclareUniverse()
+
 	// Create any needed stencils of generic functions
 	g.stencil()
 

src/cmd/compile/internal/types2/stdlib_test.go

@@ -192,6 +192,8 @@ func TestStdFixed(t *testing.T) {
 		"issue20780.go",  // types2 does not have constraints on stack size
 		"issue42058a.go", // types2 does not have constraints on channel element size
 		"issue42058b.go", // types2 does not have constraints on channel element size
+		"issue48097.go",  // go/types doesn't check validity of //go:xxx directives, and non-init bodyless function
+
 	)
 }
 

src/go/types/stdlib_test.go

@@ -194,6 +194,7 @@ func TestStdFixed(t *testing.T) {
 		"bug251.go",      // issue #34333 which was exposed with fix for #34151
 		"issue42058a.go", // go/types does not have constraints on channel element size
 		"issue42058b.go", // go/types does not have constraints on channel element size
+		"issue48097.go",  // go/types doesn't check validity of //go:xxx directives, and non-init bodyless function
 	)
 }
 

test/fixedbugs/issue48097.go

@@ -0,0 +1,12 @@
+// errorcheck -complete
+
+// 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 p
+
+func F() // ERROR "missing function body"
+
+//go:noescape
+func f() {} // ERROR "can only use //go:noescape with external func implementations"