[dev.typeparams] cmd/compile/internal/ir: more useful Fatalfs

This CL just adds some additional details to existing Fatalf messages
that make them more useful for identifying what went wrong.

Change-Id: Icba0d943ccfb1b810a1ede0977cc8cf22b2afde5
Reviewed-on: https://go-review.googlesource.com/c/go/+/320612
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

src/cmd/compile/internal/ir/func.go

@@ -279,7 +279,7 @@ func FuncSymName(s *types.Sym) string {
 // MarkFunc marks a node as a function.
 func MarkFunc(n *Name) {
 	if n.Op() != ONAME || n.Class != Pxxx {
-		base.Fatalf("expected ONAME/Pxxx node, got %v", n)
+		base.FatalfAt(n.Pos(), "expected ONAME/Pxxx node, got %v (%v/%v)", n, n.Op(), n.Class)
 	}
 
 	n.Class = PFUNC

src/cmd/compile/internal/ir/node.go

@@ -563,7 +563,7 @@ func OuterValue(n Node) Node {
 	for {
 		switch nn := n; nn.Op() {
 		case OXDOT:
-			base.Fatalf("OXDOT in walk")
+			base.FatalfAt(n.Pos(), "OXDOT in walk: %v", n)
 		case ODOT:
 			nn := nn.(*SelectorExpr)
 			n = nn.X

src/cmd/compile/internal/ir/val.go

@@ -66,7 +66,7 @@ func Float64Val(v constant.Value) float64 {
 
 func AssertValidTypeForConst(t *types.Type, v constant.Value) {
 	if !ValidTypeForConst(t, v) {
-		base.Fatalf("%v does not represent %v", t, v)
+		base.Fatalf("%v does not represent %v (%v)", t, v, v.Kind())
 	}
 }