cmd/compile: fix storeOrder

storeOrder visits values in DFS order. It should "break" after
pushing one argument to stack, instead of "continue".

Fixes #19179.

Change-Id: I561afb44213df40ebf8bf7d28e0fd00f22a81ac0
Reviewed-on: https://go-review.googlesource.com/37250
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -400,7 +400,7 @@ func storeOrder(values []*Value, sset *sparseSet, storeNumber []int32) []*Value
 					stack = append(stack, a)
 					sset.add(a.ID)
 					argsdone = false
-					continue
+					break
 				}
 				if storeNumber[a.ID]/3 > max {
 					max = storeNumber[a.ID] / 3

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

@@ -55,3 +55,44 @@ func isSingleLiveMem(f *Func) bool {
 	}
 	return true
 }
+
+func TestStoreOrder(t *testing.T) {
+	// In the function below, v2 depends on v3 and v4, v4 depends on v3, and v3 depends on store v5.
+	// storeOrder did not handle this case correctly.
+	c := testConfig(t)
+	fun := Fun(c, "entry",
+		Bloc("entry",
+			Valu("mem0", OpInitMem, TypeMem, 0, nil),
+			Valu("a", OpAdd64, TypeInt64, 0, nil, "b", "c"),            // v2
+			Valu("b", OpLoad, TypeInt64, 0, nil, "ptr", "mem1"),        // v3
+			Valu("c", OpNeg64, TypeInt64, 0, nil, "b"),                 // v4
+			Valu("mem1", OpStore, TypeMem, 8, nil, "ptr", "v", "mem0"), // v5
+			Valu("mem2", OpStore, TypeMem, 0, nil, "ptr", "a", "mem1"),
+			Valu("ptr", OpConst64, TypeInt64, 0xABCD, nil),
+			Valu("v", OpConst64, TypeInt64, 12, nil),
+			Goto("exit")),
+		Bloc("exit",
+			Exit("mem2")))
+
+	CheckFunc(fun.f)
+	order := storeOrder(fun.f.Blocks[0].Values, fun.f.newSparseSet(fun.f.NumValues()), make([]int32, fun.f.NumValues()))
+
+	// check that v2, v3, v4 is sorted after v5
+	var ai, bi, ci, si int
+	for i, v := range order {
+		switch v.ID {
+		case 2:
+			ai = i
+		case 3:
+			bi = i
+		case 4:
+			ci = i
+		case 5:
+			si = i
+		}
+	}
+	if ai < si || bi < si || ci < si {
+		t.Logf("Func: %s", fun.f)
+		t.Errorf("store order is wrong: got %v, want v2 v3 v4 after v5", order)
+	}
+}