Support IfThenElse instruction pattern for arbitrary smi constants.

tests/language/if_conversion_vm_test.dart

Index: tests/language/if_conversion_vm_test.dart
diff --git a/tests/language/if_conversion_vm_test.dart b/tests/language/if_conversion_vm_test.dart
index 22e6203291f96ac6251f204399738b29cf7f2be9..8fc82e2babaca09cf65c78dda56166ee767d567b 100644
--- a/tests/language/if_conversion_vm_test.dart
+++ b/tests/language/if_conversion_vm_test.dart
@@ -30,6 +30,12 @@ const POWER_OF_2 = 0x1000000000;
 
 bigPower(i) => (i == 11) ? 0 : POWER_OF_2;
 
+cse(i) {
+  final a = i == 0 ? 0 : 1;
+  final b = i == 0 ? 2 : 3;
+  return a + b;
+}
+
 main() {
   for (var i = 0; i < 10000; i++) {
     f1(i);
@@ -48,6 +54,7 @@ main() {
     f14(i);
     f15(i);
     f16(i);
+    cse(i);
     bigPower(i);
   }
 
@@ -89,4 +96,7 @@ main() {
 
   Expect.equals(0, bigPower(11));
   Expect.equals(POWER_OF_2, bigPower(12));
+
+  Expect.equals(2, cse(0));
+  Expect.equals(4, cse(1));
 }