ensure proper evaluation order if compare can panic

src/cmd/compile/internal/compare/compare.go

@@ -166,10 +166,14 @@ func calculateCostForType(t *types.Type) int64 {
 // It works by building a list of boolean conditions to satisfy.
 // Conditions must be evaluated in the returned order and
 // properly short-circuited by the caller.
-func EqStruct(t *types.Type, np, nq ir.Node) []ir.Node {
+// The first return value is the flattened list of conditions,
+// the second value is a boolean indicating whether any of the
+// comparisons could panic.
+func EqStruct(t *types.Type, np, nq ir.Node) ([]ir.Node, bool) {
 	// The conditions are a list-of-lists. Conditions are reorderable
 	// within each inner list. The outer lists must be evaluated in order.
 	var conds [][]ir.Node
+	var canPanic bool
 	conds = append(conds, []ir.Node{})
 	and := func(n ir.Node) {
 		i := len(conds) - 1
@@ -187,9 +191,14 @@ func EqStruct(t *types.Type, np, nq ir.Node) []ir.Node {
 			continue
 		}
 
+		typeCanPanic := EqCanPanic(f.Type)
+		if !canPanic {
+			canPanic = typeCanPanic
+		}
+
 		// Compare non-memory fields with field equality.
 		if !IsRegularMemory(f.Type) {
-			if EqCanPanic(f.Type) {
+			if typeCanPanic {
 				// Enforce ordering by starting a new set of reorderable conditions.
 				conds = append(conds, []ir.Node{})
 			}
@@ -203,7 +212,7 @@ func EqStruct(t *types.Type, np, nq ir.Node) []ir.Node {
 			default:
 				and(ir.NewBinaryExpr(base.Pos, ir.OEQ, p, q))
 			}
-			if EqCanPanic(f.Type) {
+			if typeCanPanic {
 				// Also enforce ordering after something that can panic.
 				conds = append(conds, []ir.Node{})
 			}
@@ -238,7 +247,7 @@ func EqStruct(t *types.Type, np, nq ir.Node) []ir.Node {
 		})
 		flatConds = append(flatConds, c...)
 	}
-	return flatConds
+	return flatConds, canPanic
 }
 
 // EqString returns the nodes

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

@@ -530,7 +530,7 @@ func eqFunc(t *types.Type) *ir.Func {
 			qi := ir.NewIndexExpr(tmpPos, nq, ir.NewInt(tmpPos, 0))
 			qi.SetBounded(true)
 			qi.SetType(t.Elem())
-			flatConds := compare.EqStruct(t.Elem(), pi, qi)
+			flatConds, canPanic := compare.EqStruct(t.Elem(), pi, qi)
 			for _, c := range flatConds {
 				if isCall(c) {
 					hasCallExprs = true
@@ -538,7 +538,7 @@ func eqFunc(t *types.Type) *ir.Func {
 					allCallExprs = false
 				}
 			}
-			if !hasCallExprs || allCallExprs {
+			if !hasCallExprs || allCallExprs || canPanic {
 				checkAll(1, true, func(pi, qi ir.Node) ir.Node {
 					// p[i] == q[i]
 					return ir.NewBinaryExpr(base.Pos, ir.OEQ, pi, qi)
@@ -546,7 +546,7 @@ func eqFunc(t *types.Type) *ir.Func {
 			} else {
 				checkAll(4, false, func(pi, qi ir.Node) ir.Node {
 					expr = nil
-					flatConds := compare.EqStruct(t.Elem(), pi, qi)
+					flatConds, _ := compare.EqStruct(t.Elem(), pi, qi)
 					if len(flatConds) == 0 {
 						return ir.NewBool(base.Pos, true)
 					}
@@ -559,7 +559,7 @@ func eqFunc(t *types.Type) *ir.Func {
 				})
 				checkAll(2, true, func(pi, qi ir.Node) ir.Node {
 					expr = nil
-					flatConds := compare.EqStruct(t.Elem(), pi, qi)
+					flatConds, _ := compare.EqStruct(t.Elem(), pi, qi)
 					for _, c := range flatConds {
 						if isCall(c) {
 							and(c)
@@ -576,7 +576,7 @@ func eqFunc(t *types.Type) *ir.Func {
 		}
 
 	case types.TSTRUCT:
-		flatConds := compare.EqStruct(t, np, nq)
+		flatConds, _ := compare.EqStruct(t, np, nq)
 		if len(flatConds) == 0 {
 			fn.Body.Append(ir.NewAssignStmt(base.Pos, nr, ir.NewBool(base.Pos, true)))
 		} else {

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

@@ -228,7 +228,7 @@ func walkCompare(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
 	cmpl = safeExpr(cmpl, init)
 	cmpr = safeExpr(cmpr, init)
 	if t.IsStruct() {
-		conds := compare.EqStruct(t, cmpl, cmpr)
+		conds, _ := compare.EqStruct(t, cmpl, cmpr)
 		if n.Op() == ir.OEQ {
 			for _, cond := range conds {
 				and(cond)

test/fixedbugs/issue8606.go

@@ -34,6 +34,10 @@ func main() {
 		f any
 		i int
 	}
+	type S4 struct {
+		a [1000]byte
+		b any
+	}
 	b := []byte{1}
 	s1 := S3{func() {}, 0}
 	s2 := S3{func() {}, 1}
@@ -72,6 +76,7 @@ func main() {
 		{false, T3{s: "fooz", j: b}, T3{s: "bar", j: b}},
 		{true, A{s1, s2}, A{s2, s1}},
 		{true, s1, s2},
+		{false, S4{[1000]byte{0}, func() {}}, S4{[1000]byte{1}, func() {}}},
 	} {
 		f := func() {
 			defer func() {