[turbofan] Simplify representations selection for phi.

test/cctest/compiler/test-simplified-lowering.cc

Index: test/cctest/compiler/test-simplified-lowering.cc
diff --git a/test/cctest/compiler/test-simplified-lowering.cc b/test/cctest/compiler/test-simplified-lowering.cc
index 1700e330f8e36a9366118f935ae79d31b536da20..62eb5bae1801ce030aa753884f3f405a4bdb0741 100644
--- a/test/cctest/compiler/test-simplified-lowering.cc
+++ b/test/cctest/compiler/test-simplified-lowering.cc
@@ -1994,8 +1994,7 @@ TEST(PhiRepresentation) {
        kRepWord32 | kTypeNumber},
       {Type::Signed32(), Type::Signed32(), kMachInt32, kMachInt32},
       {Type::Unsigned32(), Type::Unsigned32(), kMachInt32, kMachUint32},
-      {Type::Number(), Type::Signed32(), kMachInt32, kMachFloat64},
-      {Type::Signed32(), Type::String(), kMachInt32, kMachAnyTagged}};
+      {Type::Number(), Type::Signed32(), kMachInt32, kRepWord32 | kTypeNumber}};
 
   for (auto const d : test_data) {
     TestingGraph t(d.arg1, d.arg2, Type::Boolean());