diff --git a/src/cmd/compile/internal/ir/mini.go b/src/cmd/compile/internal/ir/mini.go
index 7bc816356da..801a48a78e4 100644
--- a/src/cmd/compile/internal/ir/mini.go
+++ b/src/cmd/compile/internal/ir/mini.go
@@ -7,7 +7,6 @@
 package ir
 
 import (
-	"cmd/compile/internal/base"
 	"cmd/compile/internal/types"
 	"cmd/internal/src"
 	"fmt"
@@ -67,8 +66,6 @@ func (n *miniNode) SetTypecheck(x uint8) {
 	n.bits.set2(miniTypecheckShift, x)
 }
 
-func (n *miniNode) SetDiag(x bool) { base.AssertfAt(!x, n.Pos(), "SetDiag") }
-
 func (n *miniNode) Walked() bool     { return n.bits&miniWalked != 0 }
 func (n *miniNode) SetWalked(x bool) { n.bits.set(miniWalked, x) }
 
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index 390af6aad21..5e5868abb2a 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -46,7 +46,6 @@ type Node interface {
 	// Storage for analysis passes.
 	Esc() uint16
 	SetEsc(x uint16)
-	SetDiag(x bool)
 
 	// Typecheck values:
 	//  0 means the node is not typechecked
diff --git a/src/cmd/compile/internal/typecheck/const.go b/src/cmd/compile/internal/typecheck/const.go
index 79387dd7353..1422ab00312 100644
--- a/src/cmd/compile/internal/typecheck/const.go
+++ b/src/cmd/compile/internal/typecheck/const.go
@@ -98,10 +98,7 @@ func convlit1(n ir.Node, t *types.Type, explicit bool, context func() string) ir
 		}
 		n = ir.Copy(n)
 		if t == nil {
-			base.Errorf("use of untyped nil")
-			n.SetDiag(true)
-			n.SetType(nil)
-			return n
+			base.Fatalf("use of untyped nil")
 		}
 
 		if !t.HasNil() {
@@ -199,13 +196,12 @@ func convlit1(n ir.Node, t *types.Type, explicit bool, context func() string) ir
 	}
 
 	if explicit {
-		base.Errorf("cannot convert %L to type %v", n, t)
+		base.Fatalf("cannot convert %L to type %v", n, t)
 	} else if context != nil {
-		base.Errorf("cannot use %L as type %v in %s", n, t, context())
+		base.Fatalf("cannot use %L as type %v in %s", n, t, context())
 	} else {
-		base.Errorf("cannot use %L as type %v", n, t)
+		base.Fatalf("cannot use %L as type %v", n, t)
 	}
-	n.SetDiag(true)
 
 	n.SetType(nil)
 	return n
diff --git a/src/cmd/compile/internal/typecheck/expr.go b/src/cmd/compile/internal/typecheck/expr.go
index 50271403415..11e5268feb2 100644
--- a/src/cmd/compile/internal/typecheck/expr.go
+++ b/src/cmd/compile/internal/typecheck/expr.go
@@ -413,11 +413,7 @@ func tcConv(n *ir.ConvExpr) ir.Node {
 	}
 	op, why := Convertop(n.X.Op() == ir.OLITERAL, t, n.Type())
 	if op == ir.OXXX {
-		base.Errorf("cannot convert %L to type %v%s", n.X, n.Type(), why)
-		n.SetDiag(true)
-		n.SetOp(ir.OCONV)
-		n.SetType(nil)
-		return n
+		base.Fatalf("cannot convert %L to type %v%s", n.X, n.Type(), why)
 	}
 
 	n.SetOp(op)
diff --git a/src/cmd/compile/internal/typecheck/func.go b/src/cmd/compile/internal/typecheck/func.go
index 630a17b7f2b..298af2aeeb7 100644
--- a/src/cmd/compile/internal/typecheck/func.go
+++ b/src/cmd/compile/internal/typecheck/func.go
@@ -357,8 +357,7 @@ func tcCall(n *ir.CallExpr, top int) ir.Node {
 	l = n.X
 	if l.Op() == ir.OTYPE {
 		if n.IsDDD {
-			base.Errorf("invalid use of ... in type conversion to %v", l.Type())
-			n.SetDiag(true)
+			base.Fatalf("invalid use of ... in type conversion to %v", l.Type())
 		}
 
 		// pick off before type-checking arguments
diff --git a/src/cmd/compile/internal/typecheck/stmt.go b/src/cmd/compile/internal/typecheck/stmt.go
index 603b9819b1c..a6ff84e7f6e 100644
--- a/src/cmd/compile/internal/typecheck/stmt.go
+++ b/src/cmd/compile/internal/typecheck/stmt.go
@@ -315,8 +315,7 @@ func tcGoDefer(n *ir.GoDeferStmt) {
 
 	// The syntax made sure it was a call, so this must be
 	// a conversion.
-	n.SetDiag(true)
-	base.ErrorfAt(n.Pos(), "%s requires function call, not conversion", what)
+	base.FatalfAt(n.Pos(), "%s requires function call, not conversion", what)
 }
 
 // tcIf typechecks an OIF node.
diff --git a/src/cmd/compile/internal/typecheck/typecheck.go b/src/cmd/compile/internal/typecheck/typecheck.go
index 7b9e35b4440..13c19dbdaca 100644
--- a/src/cmd/compile/internal/typecheck/typecheck.go
+++ b/src/cmd/compile/internal/typecheck/typecheck.go
@@ -454,10 +454,8 @@ func typecheck1(n ir.Node, top int) ir.Node {
 	case ir.ONONAME:
 		// Note: adderrorname looks for this string and
 		// adds context about the outer expression
-		base.ErrorfAt(n.Pos(), "undefined: %v", n.Sym())
-		n.SetDiag(true)
-		n.SetType(nil)
-		return n
+		base.FatalfAt(n.Pos(), "undefined: %v", n.Sym())
+		panic("unreachable")
 
 	case ir.ONAME:
 		n := n.(*ir.Name)
@@ -828,8 +826,7 @@ func typecheck1(n ir.Node, top int) ir.Node {
 
 	case ir.OTYPESW:
 		n := n.(*ir.TypeSwitchGuard)
-		base.Errorf("use of .(type) outside type switch")
-		n.SetDiag(true)
+		base.Fatalf("use of .(type) outside type switch")
 		return n
 
 	case ir.ODCLFUNC:
@@ -1374,7 +1371,7 @@ notenough:
 			base.Errorf("not enough arguments to %v%s", op, details)
 		}
 		if n != nil {
-			n.SetDiag(true)
+			base.Fatalf("invalid call")
 		}
 	}
 	return
@@ -1521,13 +1518,7 @@ func typecheckarraylit(elemType *types.Type, bound int64, elts []ir.Node, ctx st
 			elt.Key = Expr(elt.Key)
 			key = IndexConst(elt.Key)
 			if key < 0 {
-				if key == -2 {
-					base.Errorf("index too large")
-				} else {
-					base.Errorf("index must be non-negative integer constant")
-				}
-				elt.Key.SetDiag(true)
-				key = -(1 << 30) // stay negative for a while
+				base.Fatalf("invalid index: %v", elt.Key)
 			}
 			kv = elt
 			r = elt.Value