Add compressed oops to VM info string, for HotSpot 20.0

example

OpenJDK Client VM (build 20.0-b11-internal, mixed mode, sharing)
OpenJDK 64-Bit Server VM (build 20.0-b11-internal, mixed mode, compressed oops)

vm_info_string.diff

diff -r f0f676c5a2c6 src/share/vm/runtime/vm_version.cpp
--- a/src/share/vm/runtime/vm_version.cpp       Tue Mar 15 19:30:16 2011 -0700
+++ b/src/share/vm/runtime/vm_version.cpp       Thu Nov 10 14:41:05 2011 +0800
@@ -137,18 +137,46 @@
 #endif
 }
 
+enum {
+  mode_bits = 2,
+  sharing_bits = 1,
+  coops_bits = 1
+};
+
+enum {
+  mode_shift = 0,
+  sharing_shift = mode_bits,
+  coops_shift = sharing_shift + sharing_bits
+};
+
+const char* unknown_info = "unknown VM";
+
+const char* info_strs[] = {                     // coops | sharing | mode
+  "interpreted mode",                           //     0 |       0 |   00
+  "mixed mode",                                 //     0 |       0 |   01
+  "compiled mode",                              //     0 |       0 |   10
+  unknown_info,                                 //     0 |       0 |   11
+  "interpreted mode, sharing",                  //     0 |       1 |   00
+  "mixed mode, sharing",                        //     0 |       1 |   01
+  "compiled mode, sharing",                     //     0 |       1 |   10
+  unknown_info,                                 //     0 |       1 |   11
+  "interpreted mode, compressed oops",          //     1 |       0 |   00
+  "mixed mode, compressed oops",                //     1 |       0 |   01
+  "compiled mode, compressed oops",             //     1 |       0 |   10
+  unknown_info,                                 //     1 |       0 |   11
+  "interpreted mode, sharing, compressed oops", //     1 |       1 |   00
+  "mixed mode, sharing, compressed oops",       //     1 |       1 |   01
+  "compiled mode, sharing, compressed oops",    //     1 |       1 |   10
+  unknown_info                                  //     1 |       1 |   11
+};
 
 const char* Abstract_VM_Version::vm_info_string() {
-  switch (Arguments::mode()) {
-    case Arguments::_int:
-      return UseSharedSpaces ? "interpreted mode, sharing" : "interpreted mode";
-    case Arguments::_mixed:
-      return UseSharedSpaces ? "mixed mode, sharing"       :  "mixed mode";
-    case Arguments::_comp:
-      return UseSharedSpaces ? "compiled mode, sharing"    : "compiled mode";
-  };
-  ShouldNotReachHere();
-  return "";
+  int index = Arguments::mode() << mode_shift
+            | (UseSharedSpaces ? 1 : 0) << sharing_shift
+            | (UseCompressedOops ? 1 : 0) << coops_shift;
+  const char* info_str = info_strs[index];
+  if (unknown_info == info_str) ShouldNotReachHere();
+  return info_str;
 }
 
 // NOTE: do *not* use stringStream. this function is called by
diff -r f0f676c5a2c6 src/share/vm/utilities/vmError.cpp
--- a/src/share/vm/utilities/vmError.cpp        Tue Mar 15 19:30:16 2011 -0700
+++ b/src/share/vm/utilities/vmError.cpp        Thu Nov 10 14:41:05 2011 +0800
@@ -434,12 +434,11 @@
      st->print_cr("#");
      JDK_Version::current().to_string(buf, sizeof(buf));
      st->print_cr("# JRE version: %s", buf);
-     st->print_cr("# Java VM: %s (%s %s %s %s)",
+     st->print_cr("# Java VM: %s (%s %s %s)",
                    Abstract_VM_Version::vm_name(),
                    Abstract_VM_Version::vm_release(),
                    Abstract_VM_Version::vm_info_string(),
-                   Abstract_VM_Version::vm_platform_string(),
-                   UseCompressedOops ? "compressed oops" : ""
+                   Abstract_VM_Version::vm_platform_string()
                  );
 
   STEP(60, "(printing problematic frame)")