cmd/compile: in poset, simplify usage of CheckIntegrity

Instead of returning an error, just panic: the function is
used only for debugging purposes anyway.

Change-Id: Ie81b2309daaf1efb9470992391534bce2141b3c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/196779Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/ssa/poset.go

@@ -5,7 +5,6 @@
 package ssa
 
 import (
-	"errors"
 	"fmt"
 	"os"
 )
@@ -625,13 +624,12 @@ func (po *poset) setnoneq(id1, id2 ID) {
 
 // CheckIntegrity verifies internal integrity of a poset. It is intended
 // for debugging purposes.
-func (po *poset) CheckIntegrity() (err error) {
+func (po *poset) CheckIntegrity() {
 	// Record which index is a constant
 	constants := newBitset(int(po.lastidx + 1))
 	for _, c := range po.constants {
 		if idx, ok := po.values[c.ID]; !ok {
-			err = errors.New("node missing for constant")
-			return err
+			panic("node missing for constant")
 		} else {
 			constants.Set(idx)
 		}
@@ -642,34 +640,27 @@ func (po *poset) CheckIntegrity() (err error) {
 	seen := newBitset(int(po.lastidx + 1))
 	for ridx, r := range po.roots {
 		if r == 0 {
-			err = errors.New("empty root")
-			return
+			panic("empty root")
 		}
 
 		po.dfs(r, false, func(i uint32) bool {
 			if seen.Test(i) {
-				err = errors.New("duplicate node")
-				return true
+				panic("duplicate node")
 			}
 			seen.Set(i)
 			if constants.Test(i) {
 				if ridx != 0 {
-					err = errors.New("constants not in the first DAG")
-					return true
+					panic("constants not in the first DAG")
 				}
 			}
 			return false
 		})
-		if err != nil {
-			return
-		}
 	}
 
 	// Verify that values contain the minimum set
 	for id, idx := range po.values {
 		if !seen.Test(idx) {
-			err = fmt.Errorf("spurious value [%d]=%d", id, idx)
-			return
+			panic(fmt.Errorf("spurious value [%d]=%d", id, idx))
 		}
 	}
 
@@ -677,17 +668,13 @@ func (po *poset) CheckIntegrity() (err error) {
 	for i, n := range po.nodes {
 		if n.l|n.r != 0 {
 			if !seen.Test(uint32(i)) {
-				err = fmt.Errorf("children of unknown node %d->%v", i, n)
-				return
+				panic(fmt.Errorf("children of unknown node %d->%v", i, n))
 			}
 			if n.l.Target() == uint32(i) || n.r.Target() == uint32(i) {
-				err = fmt.Errorf("self-loop on node %d", i)
-				return
+				panic(fmt.Errorf("self-loop on node %d", i))
 			}
 		}
 	}
-
-	return
 }
 
 // CheckEmpty checks that a poset is completely empty.

src/cmd/compile/internal/ssa/poset_test.go

@@ -146,9 +146,7 @@ func testPosetOps(t *testing.T, unsigned bool, ops []posetTestOp) {
 			po.DotDump(fmt.Sprintf("op%d.dot", idx), fmt.Sprintf("Last op: %v", op))
 		}
 
-		if err := po.CheckIntegrity(); err != nil {
-			t.Fatalf("op%d%v: integrity error: %v", idx, op, err)
-		}
+		po.CheckIntegrity()
 	}
 
 	// Check that the poset is completely empty