Use only single characters for ssa types.

lib/compiler/implementation/ssa/tracer.dart

Index: lib/compiler/implementation/ssa/tracer.dart
diff --git a/lib/compiler/implementation/ssa/tracer.dart b/lib/compiler/implementation/ssa/tracer.dart
index c4c58ebafd0dded8deb9a6b8b248a1019678f3b3..dc91f69cec9fd54f5bfe0b70c7791790bc0373d6 100644
--- a/lib/compiler/implementation/ssa/tracer.dart
+++ b/lib/compiler/implementation/ssa/tracer.dart
@@ -167,8 +167,8 @@ class HInstructionStringifier implements HVisitor<String> {
     String prefix;
     HType type = instruction.propagatedType;
     switch (type) {
-      case HType.MUTABLE_ARRAY: prefix = 'a'; break;
-      case HType.READABLE_ARRAY: prefix = 'roa'; break;
+      case HType.MUTABLE_ARRAY: prefix = 'm'; break;
+      case HType.READABLE_ARRAY: prefix = 'a'; break;
       case HType.BOOLEAN: prefix = 'b'; break;
       case HType.INTEGER: prefix = 'i'; break;
       case HType.DOUBLE: prefix = 'd'; break;
@@ -176,7 +176,7 @@ class HInstructionStringifier implements HVisitor<String> {
       case HType.STRING: prefix = 's'; break;
       case HType.UNKNOWN: prefix = 'v'; break;
       case HType.CONFLICTING: prefix = 'c'; break;
-      case HType.STRING_OR_ARRAY: prefix = 'sa'; break;
+      case HType.STRING_OR_ARRAY: prefix = 'r'; break;
       default: unreachable();
     }
     return "$prefix${instruction.id}";