[turbofan] Fix select lowering.

test/unittests/compiler/select-lowering-unittest.cc

Index: test/unittests/compiler/select-lowering-unittest.cc
diff --git a/test/unittests/compiler/select-lowering-unittest.cc b/test/unittests/compiler/select-lowering-unittest.cc
index 6dbd7ad73d99608931c8a6d06c1781b656b38bd3..51efc83f87c2eb15d4d8f6edfe3ac3a7ef77a34b 100644
--- a/test/unittests/compiler/select-lowering-unittest.cc
+++ b/test/unittests/compiler/select-lowering-unittest.cc
@@ -10,6 +10,7 @@
 using testing::AllOf;
 using testing::Capture;
 using testing::CaptureEq;
+using testing::Not;
 
 namespace v8 {
 namespace internal {
@@ -33,12 +34,12 @@ TEST_F(SelectLoweringTest, SelectWithSameConditions) {
   Node* const p2 = Parameter(2);
   Node* const p3 = Parameter(3);
   Node* const p4 = Parameter(4);
+  Node* const s0 = graph()->NewNode(common()->Select(kMachInt32), p0, p1, p2);
 
   Capture<Node*> branch;
   Capture<Node*> merge;
   {
-    Reduction const r =
-        Reduce(graph()->NewNode(common()->Select(kMachInt32), p0, p1, p2));
+    Reduction const r = Reduce(s0);
     ASSERT_TRUE(r.Changed());
     EXPECT_THAT(
         r.replacement(),
@@ -55,6 +56,15 @@ TEST_F(SelectLoweringTest, SelectWithSameConditions) {
     ASSERT_TRUE(r.Changed());
     EXPECT_THAT(r.replacement(), IsPhi(kMachInt32, p3, p4, CaptureEq(&merge)));
   }
+  {
+    // We must not reuse the diamond if it is reachable from either else/then
+    // values of the Select, because the resulting graph can not be scheduled.
+    Reduction const r =
+        Reduce(graph()->NewNode(common()->Select(kMachInt32), p0, s0, p0));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_THAT(r.replacement(),
+                IsPhi(kMachInt32, s0, p0, Not(CaptureEq(&merge))));
+  }
 }
 
 }  // namespace compiler