--- a/hotspot/src/share/vm/adlc/adlparse.cpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/adlparse.cpp	Fri Mar 27 10:57:42 2015 +0100
@@ -800,6 +800,7 @@
       }
       if (strcmp(token,"reg_def")==0)          { reg_def_parse(); }
       else if (strcmp(token,"reg_class")==0)   { reg_class_parse(); }
+      else if (strcmp(token, "reg_class_dynamic") == 0) { reg_class_dynamic_parse(); }
       else if (strcmp(token,"alloc_class")==0) { alloc_class_parse(); }
       else if (strcmp(token,"#define")==0)     { preproc_define(); }
       else { parse_err(SYNERR, "bad token %s inside register block.\n", token); break; }
@@ -2323,11 +2324,12 @@
   // Debug Stuff
   if (_AD._adl_debug >1) fprintf(stderr,"Register Class: %s\n", cname);
 
-  RegClass *reg_class = _AD._register->addRegClass(cname);
-
-  // Collect registers in class
   skipws();
   if (_curchar == '(') {
+    // A register list is defined for the register class.
+    // Collect registers into a generic RegClass register class.
+    RegClass* reg_class = _AD._register->addRegClass<RegClass>(cname);
+
     next_char();                  // Skip '('
     skipws();
     while (_curchar != ')') {
@@ -2352,12 +2354,15 @@
     }
     next_char();                  // Skip closing ')'
   } else if (_curchar == '%') {
+    // A code snippet is defined for the register class.
+    // Collect the code snippet into a CodeSnippetRegClass register class.
+    CodeSnippetRegClass* reg_class = _AD._register->addRegClass<CodeSnippetRegClass>(cname);
     char *code = find_cpp_block("reg class");
     if (code == NULL) {
       parse_err(SYNERR, "missing code declaration for reg class.\n");
       return;
     }
-    reg_class->_user_defined = code;
+    reg_class->set_code_snippet(code);
     return;
   }
 
@@ -2374,6 +2379,87 @@
   return;
 }
 
+//------------------------------reg_class_dynamic_parse------------------------
+void ADLParser::reg_class_dynamic_parse(void) {
+  char *cname; // Name of dynamic register class being defined
+
+  // Get register class name
+  skipws();
+  cname = get_ident();
+  if (cname == NULL) {
+    parse_err(SYNERR, "missing dynamic register class name after 'reg_class_dynamic'\n");
+    return;
+  }
+
+  if (_AD._adl_debug > 1) {
+    fprintf(stdout, "Dynamic Register Class: %s\n", cname);
+  }
+
+  skipws();
+  if (_curchar != '(') {
+    parse_err(SYNERR, "missing '(' at the beginning of reg_class_dynamic definition\n");
+    return;
+  }
+  next_char();
+  skipws();
+
+  // Collect two register classes and the C++ code representing the condition code used to
+  // select between the two classes into a ConditionalRegClass register class.
+  ConditionalRegClass* reg_class = _AD._register->addRegClass<ConditionalRegClass>(cname);
+  int i;
+  for (i = 0; i < 2; i++) {
+    char* name = get_ident();
+    if (name == NULL) {
+      parse_err(SYNERR, "missing class identifier inside reg_class_dynamic list.\n");
+      return;
+    }
+    RegClass* rc = _AD._register->getRegClass(name);
+    if (rc == NULL) {
+      parse_err(SEMERR, "unknown identifier %s inside reg_class_dynamic list.\n", name);
+    } else {
+      reg_class->set_rclass_at_index(i, rc);
+    }
+
+    skipws();
+    if (_curchar == ',') {
+      next_char();
+      skipws();
+    } else {
+      parse_err(SYNERR, "missing separator ',' inside reg_class_dynamic list.\n");
+    }
+  }
+
+  // Collect the condition code.
+  skipws();
+  if (_curchar == '%') {
+    char* code = find_cpp_block("reg class dynamic");
+    if (code == NULL) {
+       parse_err(SYNERR, "missing code declaration for reg_class_dynamic.\n");
+       return;
+    }
+    reg_class->set_condition_code(code);
+  } else {
+    parse_err(SYNERR, "missing %% at the beginning of code block in reg_class_dynamic definition\n");
+    return;
+  }
+
+  skipws();
+  if (_curchar != ')') {
+    parse_err(SYNERR, "missing ')' at the end of reg_class_dynamic definition\n");
+    return;
+  }
+  next_char();
+
+  skipws();
+  if (_curchar != ';') {
+    parse_err(SYNERR, "missing ';' at the end of reg_class_dynamic definition.\n");
+    return;
+  }
+  next_char();                    // Skip trailing ';'
+
+  return;
+}
+
 //------------------------------alloc_class_parse------------------------------
 void ADLParser::alloc_class_parse(void) {
   char *name;                     // Name of allocation class being defined

--- a/hotspot/src/share/vm/adlc/adlparse.hpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/adlparse.hpp	Fri Mar 27 10:57:42 2015 +0100
@@ -53,6 +53,8 @@
 // ***** Register Section *****
 class RegDef;
 class RegClass;
+class CodeSnippetRegClass;
+class ConditionalRegClass;
 class AllocClass;
 class ResourceForm;
 // ***** Pipeline Section *****
@@ -125,6 +127,7 @@
   // Parse components of the register section
   void reg_def_parse(void);              // Parse register definition
   void reg_class_parse(void);            // Parse register class definition
+  void reg_class_dynamic_parse(void);    // Parse dynamic register class definition
   void alloc_class_parse(void);          // Parse allocation class definition
 
   // Parse components of the definition section

--- a/hotspot/src/share/vm/adlc/archDesc.cpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/archDesc.cpp	Fri Mar 27 10:57:42 2015 +0100
@@ -908,7 +908,7 @@
 void ArchDesc::set_stack_or_reg(const char *reg_class_name) {
   if( _register ) {
     RegClass *reg_class  = _register->getRegClass(reg_class_name);
-    reg_class->_stack_or_reg = true;
+    reg_class->set_stack_version(true);
   }
 }
 

--- a/hotspot/src/share/vm/adlc/forms.hpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/forms.hpp	Fri Mar 27 10:57:42 2015 +0100
@@ -68,6 +68,8 @@
 class InsEncode;
 class RegDef;
 class RegClass;
+class CodeSnippetRegClass;
+class ConditionalRegClass;
 class AllocClass;
 class ResourceForm;
 class PipeClassForm;

--- a/hotspot/src/share/vm/adlc/formsopt.cpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/formsopt.cpp	Fri Mar 27 10:57:42 2015 +0100
@@ -47,13 +47,19 @@
 }
 
 // record a new register class
-RegClass *RegisterForm::addRegClass(const char *className) {
-  RegClass *regClass = new RegClass(className);
+template <typename T>
+T* RegisterForm::addRegClass(const char* className) {
+  T* regClass = new T(className);
   _rclasses.addName(className);
-  _regClass.Insert(className,regClass);
+  _regClass.Insert(className, regClass);
   return regClass;
 }
 
+// Explicit instantiation for all supported register classes.
+template RegClass* RegisterForm::addRegClass<RegClass>(const char* className);
+template CodeSnippetRegClass* RegisterForm::addRegClass<CodeSnippetRegClass>(const char* className);
+template ConditionalRegClass* RegisterForm::addRegClass<ConditionalRegClass>(const char* className);
+
 // record a new register class
 AllocClass *RegisterForm::addAllocClass(char *className) {
   AllocClass *allocClass = new AllocClass(className);
@@ -67,9 +73,9 @@
 void RegisterForm::addSpillRegClass() {
   // Stack slots start at the next available even register number.
   _reg_ctr = (_reg_ctr+7) & ~7;
-  const char *rc_name   = "stack_slots";
-  RegClass   *reg_class = new RegClass(rc_name);
-  reg_class->_stack_or_reg = true;
+  const char *rc_name = "stack_slots";
+  RegClass* reg_class = new RegClass(rc_name);
+  reg_class->set_stack_version(true);
   _rclasses.addName(rc_name);
   _regClass.Insert(rc_name,reg_class);
 }
@@ -224,9 +230,11 @@
 
 //------------------------------RegClass---------------------------------------
 // Construct a register class into which registers will be inserted
-RegClass::RegClass(const char *classid) : _stack_or_reg(false), _classid(classid), _regDef(cmpstr,hashstr, Form::arena),
-                                          _user_defined(NULL)
-{
+RegClass::RegClass(const char* classid) : _stack_or_reg(false), _classid(classid), _regDef(cmpstr, hashstr, Form::arena) {
+}
+
+RegClass::~RegClass() {
+  delete _classid;
 }
 
 // record a register in this class
@@ -305,6 +313,91 @@
   fprintf(fp,"--- done with entries for reg_class %s\n\n",_classid);
 }
 
+void RegClass::declare_register_masks(FILE* fp) {
+  const char* prefix = "";
+  const char* rc_name_to_upper = toUpper(_classid);
+  fprintf(fp, "extern const RegMask _%s%s_mask;\n", prefix,  rc_name_to_upper);
+  fprintf(fp, "inline const RegMask &%s%s_mask() { return _%s%s_mask; }\n", prefix, rc_name_to_upper, prefix, rc_name_to_upper);
+  if (_stack_or_reg) {
+    fprintf(fp, "extern const RegMask _%sSTACK_OR_%s_mask;\n", prefix, rc_name_to_upper);
+    fprintf(fp, "inline const RegMask &%sSTACK_OR_%s_mask() { return _%sSTACK_OR_%s_mask; }\n", prefix, rc_name_to_upper, prefix, rc_name_to_upper);
+  }
+  delete[] rc_name_to_upper;
+}
+
+void RegClass::build_register_masks(FILE* fp) {
+  int len = RegisterForm::RegMask_Size();
+  const char *prefix = "";
+  const char* rc_name_to_upper = toUpper(_classid);
+  fprintf(fp, "const RegMask _%s%s_mask(", prefix, rc_name_to_upper);
+
+  int i;
+  for(i = 0; i < len - 1; i++) {
+    fprintf(fp," 0x%x,", regs_in_word(i, false));
+  }
+  fprintf(fp," 0x%x );\n", regs_in_word(i, false));
+
+  if (_stack_or_reg) {
+    fprintf(fp, "const RegMask _%sSTACK_OR_%s_mask(", prefix, rc_name_to_upper);
+    for(i = 0; i < len - 1; i++) {
+      fprintf(fp," 0x%x,", regs_in_word(i, true));
+    }
+    fprintf(fp," 0x%x );\n", regs_in_word(i, true));
+  }
+  delete[] rc_name_to_upper;
+}
+
+//------------------------------CodeSnippetRegClass---------------------------
+CodeSnippetRegClass::CodeSnippetRegClass(const char* classid) : RegClass(classid), _code_snippet(NULL) {
+}
+
+CodeSnippetRegClass::~CodeSnippetRegClass() {
+  delete _code_snippet;
+}
+
+void CodeSnippetRegClass::declare_register_masks(FILE* fp) {
+  const char* prefix = "";
+  const char* rc_name_to_upper = toUpper(_classid);
+  fprintf(fp, "inline const RegMask &%s%s_mask() { %s }\n", prefix, rc_name_to_upper, _code_snippet);
+  delete[] rc_name_to_upper;
+}
+
+//------------------------------ConditionalRegClass---------------------------
+ConditionalRegClass::ConditionalRegClass(const char *classid) : RegClass(classid), _condition_code(NULL) {
+}
+
+ConditionalRegClass::~ConditionalRegClass() {
+  delete _condition_code;
+}
+
+void ConditionalRegClass::declare_register_masks(FILE* fp) {
+  const char* prefix = "";
+  const char* rc_name_to_upper = toUpper(_classid);
+  const char* rclass_0_to_upper = toUpper(_rclasses[0]->_classid);
+  const char* rclass_1_to_upper = toUpper(_rclasses[1]->_classid);
+  fprintf(fp, "inline const RegMask &%s%s_mask() {"
+              " return (%s) ?"
+              " %s%s_mask() :"
+              " %s%s_mask(); }\n",
+              prefix, rc_name_to_upper,
+              _condition_code,
+              prefix, rclass_0_to_upper,
+              prefix, rclass_1_to_upper);
+  if (_stack_or_reg) {
+    fprintf(fp, "inline const RegMask &%sSTACK_OR_%s_mask() {"
+                  " return (%s) ?"
+                  " %sSTACK_OR_%s_mask() :"
+                  " %sSTACK_OR_%s_mask(); }\n",
+                  prefix, rc_name_to_upper,
+                  _condition_code,
+                  prefix, rclass_0_to_upper,
+                  prefix, rclass_1_to_upper);
+  }
+  delete[] rc_name_to_upper;
+  delete[] rclass_0_to_upper;
+  delete[] rclass_1_to_upper;
+  return;
+}
 
 //------------------------------AllocClass-------------------------------------
 AllocClass::AllocClass(char *classid) : _classid(classid), _regDef(cmpstr,hashstr, Form::arena) {

--- a/hotspot/src/share/vm/adlc/formsopt.hpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/formsopt.hpp	Fri Mar 27 10:57:42 2015 +0100
@@ -60,6 +60,8 @@
 class InsEncode;
 class RegDef;
 class RegClass;
+class CodeSnippetRegClass;
+class ConditionalRegClass;
 class AllocClass;
 class ResourceForm;
 class PipeClassForm;
@@ -98,7 +100,8 @@
 
   void        addRegDef(char *regName, char *callingConv, char *c_conv,
                         char * idealtype, char *encoding, char* concreteName);
-  RegClass   *addRegClass(const char *className);
+  template<typename T> T* addRegClass(const char* className);
+
   AllocClass *addAllocClass(char *allocName);
   void        addSpillRegClass();
 
@@ -154,17 +157,28 @@
 };
 
 //------------------------------RegClass---------------------------------------
+// Generic register class. This register class is the internal representation
+// for the following .ad file format:
+//
+//  reg_class ptr(RAX, RBX, ...);
+//
+// where ptr is the name of the register class, RAX and RBX are registers.
+//
+// This register class allows registers to be spilled onto the stack. Spilling
+// is allowed is field _stack_or_reg is true.
 class RegClass : public Form {
 public:
   // Public Data
   const char *_classid;         // Name of class
   NameList    _regDefs;         // List of registers in class
   Dict        _regDef;          // Dictionary of registers in class
+protected:
   bool        _stack_or_reg;    // Allowed on any stack slot
-  char*       _user_defined;
 
+public:
   // Public Methods
   RegClass(const char *classid);// Constructor
+  virtual ~RegClass();
 
   void addReg(RegDef *regDef);  // Add a register to this class
 
@@ -183,6 +197,115 @@
 
   void dump();                  // Debug printer
   void output(FILE *fp);        // Write info to output files
+
+  virtual bool has_stack_version() {
+    return _stack_or_reg;
+  }
+  virtual void set_stack_version(bool flag) {
+    _stack_or_reg = flag;
+  }
+
+  virtual void declare_register_masks(FILE* fp);
+  virtual void build_register_masks(FILE* fp);
+};
+
+//------------------------------CodeSnippetRegClass----------------------------
+// Register class that has an user-defined C++ code snippet attached to it
+// to determine at runtime which register class to use. This register class is
+// the internal representation for the following .ad file format:
+//
+//  reg_class actual_dflt_reg %{
+//      if (VM_Version::has_vfp3_32()) {
+//          return DFLT_REG_mask();
+//      } else {
+//          return DFLT_LOW_REG_mask();
+//      }
+//  %}
+//
+// where DFLT_REG_mask() and DFLT_LOW_REG_mask() are the internal names of the
+// masks of register classes dflt_reg and dflt_low_reg.
+//
+// The attached code snippet can select also between more than two register classes.
+// This register class can be, however, used only if the register class is not
+// cisc-spillable (i.e., the registers of this class are not allowed on the stack,
+// which is equivalent with _stack_or_reg being false).
+class CodeSnippetRegClass : public RegClass {
+protected:
+  char* _code_snippet;
+public:
+  CodeSnippetRegClass(const char* classid);// Constructor
+  ~CodeSnippetRegClass();
+
+  void set_code_snippet(char* code) {
+    _code_snippet = code;
+  }
+  char* code_snippet() {
+    return _code_snippet;
+  }
+  void set_stack_version(bool flag) {
+    assert(false, "User defined register classes are not allowed to spill to the stack.");
+  }
+  void declare_register_masks(FILE* fp);
+  void build_register_masks(FILE* fp) {
+    // We do not need to generate register masks because we select at runtime
+    // between register masks generated for other register classes.
+    return;
+  }
+};
+
+//------------------------------ConditionalRegClass----------------------------
+// Register class that has two register classes and a runtime condition attached
+// to it. The condition is evaluated at runtime and either one of the register
+// attached register classes is selected. This register class is the internal
+// representation for the following .ad format:
+//
+//  reg_class_dynamic actual_dflt_reg(dflt_reg, low_reg,
+//                                    %{ VM_Version::has_vfp3_32() }%
+//                                    );
+//
+// This example is equivalent to the example used with the CodeSnippetRegClass
+// register class. A ConditionalRegClass works also if a register class is cisc-spillable
+// (i.e., _stack_or_reg is true), but if can select only between two register classes.
+class ConditionalRegClass : public RegClass {
+protected:
+  // reference to condition code
+  char* _condition_code;  // C++ condition code to dynamically determine which register class to use.
+
+                          // Example syntax (equivalent to previous example):
+                          //
+                          //  reg_class actual_dflt_reg(dflt_reg, low_reg,
+                          //                            %{ VM_Version::has_vfp3_32() }%
+                          //                            );
+  // reference to conditional register classes
+  RegClass* _rclasses[2]; // 0 is the register class selected if the condition code returns true
+                          // 1 is the register class selected if the condition code returns false
+public:
+  ConditionalRegClass(const char* classid);// Constructor
+  ~ConditionalRegClass();
+
+  virtual void set_stack_version(bool flag) {
+    RegClass::set_stack_version(flag);
+    assert((_rclasses[0] != NULL), "Register class NULL for condition code == true");
+    assert((_rclasses[1] != NULL), "Register class NULL for condition code == false");
+    _rclasses[0]->set_stack_version(flag);
+    _rclasses[1]->set_stack_version(flag);
+  }
+  void declare_register_masks(FILE* fp);
+  void build_register_masks(FILE* fp) {
+    // We do not need to generate register masks because we select at runtime
+    // between register masks generated for other register classes.
+    return;
+  }
+  void set_rclass_at_index(int index, RegClass* rclass) {
+    assert((0 <= index && index < 2), "Condition code can select only between two register classes");
+    _rclasses[index] = rclass;
+  }
+  void set_condition_code(char* code) {
+    _condition_code = code;
+  }
+  char* condition_code() {
+    return _condition_code;
+  }
 };
 
 //------------------------------AllocClass-------------------------------------

--- a/hotspot/src/share/vm/adlc/formssel.hpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/formssel.hpp	Fri Mar 27 10:57:42 2015 +0100
@@ -59,6 +59,8 @@
 class InsEncode;
 class RegDef;
 class RegClass;
+class CodeSnippetRegClass;
+class ConditionalRegClass;
 class AllocClass;
 class ResourceForm;
 class PipeDesc;

--- a/hotspot/src/share/vm/adlc/output_c.cpp	Mon Mar 23 11:20:38 2015 +0000
+++ b/hotspot/src/share/vm/adlc/output_c.cpp	Fri Mar 27 10:57:42 2015 +0100
@@ -138,26 +138,9 @@
     fprintf(fp_hpp,"// Register masks, one for each register class.\n");
     _register->_rclasses.reset();
     for (rc_name = NULL; (rc_name = _register->_rclasses.iter()) != NULL;) {
-      const char *prefix = "";
       RegClass *reg_class = _register->getRegClass(rc_name);
       assert(reg_class, "Using an undefined register class");
-
-      const char* rc_name_to_upper = toUpper(rc_name);
-
-      if (reg_class->_user_defined == NULL) {
-        fprintf(fp_hpp, "extern const RegMask _%s%s_mask;\n", prefix,  rc_name_to_upper);
-        fprintf(fp_hpp, "inline const RegMask &%s%s_mask() { return _%s%s_mask; }\n", prefix, rc_name_to_upper, prefix, rc_name_to_upper);
-      } else {
-        fprintf(fp_hpp, "inline const RegMask &%s%s_mask() { %s }\n", prefix, rc_name_to_upper, reg_class->_user_defined);
-      }
-
-      if (reg_class->_stack_or_reg) {
-        assert(reg_class->_user_defined == NULL, "no user defined reg class here");
-        fprintf(fp_hpp, "extern const RegMask _%sSTACK_OR_%s_mask;\n", prefix, rc_name_to_upper);
-        fprintf(fp_hpp, "inline const RegMask &%sSTACK_OR_%s_mask() { return _%sSTACK_OR_%s_mask; }\n", prefix, rc_name_to_upper, prefix, rc_name_to_upper);
-      }
-      delete[] rc_name_to_upper;
-
+      reg_class->declare_register_masks(fp_hpp);
     }
   }
 }
@@ -173,35 +156,9 @@
     fprintf(fp_cpp,"// Register masks, one for each register class.\n");
     _register->_rclasses.reset();
     for (rc_name = NULL; (rc_name = _register->_rclasses.iter()) != NULL;) {
-      const char *prefix = "";
       RegClass *reg_class = _register->getRegClass(rc_name);
       assert(reg_class, "Using an undefined register class");
-
-      if (reg_class->_user_defined != NULL) {
-        continue;
-      }
-
-      int len = RegisterForm::RegMask_Size();
-      const char* rc_name_to_upper = toUpper(rc_name);
-      fprintf(fp_cpp, "const RegMask _%s%s_mask(", prefix, rc_name_to_upper);
-
-      {
-        int i;
-        for(i = 0; i < len - 1; i++) {
-          fprintf(fp_cpp," 0x%x,", reg_class->regs_in_word(i, false));
-        }
-        fprintf(fp_cpp," 0x%x );\n", reg_class->regs_in_word(i, false));
-      }
-
-      if (reg_class->_stack_or_reg) {
-        int i;
-        fprintf(fp_cpp, "const RegMask _%sSTACK_OR_%s_mask(", prefix, rc_name_to_upper);
-        for(i = 0; i < len - 1; i++) {
-          fprintf(fp_cpp," 0x%x,",reg_class->regs_in_word(i, true));
-        }
-        fprintf(fp_cpp," 0x%x );\n",reg_class->regs_in_word(i, true));
-      }
-      delete[] rc_name_to_upper;
+      reg_class->build_register_masks(fp_cpp);
     }
   }
 }