--- old/make/bsd/makefiles/adlc.make	2013-06-04 10:02:09.000000000 -0700
+++ new/make/bsd/makefiles/adlc.make	2013-06-04 10:02:09.000000000 -0700
@@ -69,7 +69,7 @@
 # CFLAGS_WARN holds compiler options to suppress/enable warnings.
 # Compiler warnings are treated as errors
 ifneq ($(COMPILER_WARNINGS_FATAL),false)
-  CFLAGS_WARN = -Werror
+  CFLAGS_WARN = $(WARNINGS_ARE_ERRORS)
 endif
 CFLAGS += $(CFLAGS_WARN)
 
--- old/make/bsd/makefiles/gcc.make	2013-06-04 10:02:31.000000000 -0700
+++ new/make/bsd/makefiles/gcc.make	2013-06-04 10:02:31.000000000 -0700
@@ -71,6 +71,11 @@
       CC  = $(CC32)
     endif
 
+    ifeq ($(USE_CLANG), true)
+      CXX = clang++
+      CC  = clang
+    endif
+
     HOSTCXX = $(CXX)
     HOSTCC  = $(CC)
   endif
@@ -79,21 +84,79 @@
 endif
 
 
-# -dumpversion in gcc-2.91 shows "egcs-2.91.66". In later version, it only
-# prints the numbers (e.g. "2.95", "3.2.1")
-CC_VER_MAJOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f1)
-CC_VER_MINOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f2)
-
-# check for precompiled headers support
-ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 3 \) \| \( \( $(CC_VER_MAJOR) = 3 \) \& \( $(CC_VER_MINOR) \>= 4 \) \))" "0"
-# Allow the user to turn off precompiled headers from the command line.
-ifneq ($(USE_PRECOMPILED_HEADER),0)
-PRECOMPILED_HEADER_DIR=.
-PRECOMPILED_HEADER_SRC=$(GAMMADIR)/src/share/vm/precompiled/precompiled.hpp
-PRECOMPILED_HEADER=$(PRECOMPILED_HEADER_DIR)/precompiled.hpp.gch
+ifeq ($(USE_CLANG), true)
+  CC_VER_MAJOR := $(shell $(CC) -v 2>&1 | grep version | sed "s/.*version \([0-9]*\.[0-9]*\).*/\1/" | cut -d'.' -f1)
+  CC_VER_MINOR := $(shell $(CC) -v 2>&1 | grep version | sed "s/.*version \([0-9]*\.[0-9]*\).*/\1/" | cut -d'.' -f2)
+else
+  # -dumpversion in gcc-2.91 shows "egcs-2.91.66". In later version, it only
+  # prints the numbers (e.g. "2.95", "3.2.1")
+  CC_VER_MAJOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f1)
+  CC_VER_MINOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f2)
 endif
+
+ifeq ($(USE_CLANG), true)
+  # clang has precompiled headers support by default, but the user can switch
+  # it off by using 'USE_PRECOMPILED_HEADER=0'.
+  ifdef LP64
+    ifeq ($(USE_PRECOMPILED_HEADER),)
+      USE_PRECOMPILED_HEADER=1
+    endif
+  else
+    # We don't support precompiled headers on 32-bit builds because there some files are
+    # compiled with -fPIC while others are compiled without (see 'NONPIC_OBJ_FILES' rules.make)
+    # Clang produces an error if the PCH file was compiled with other options than the actual compilation unit.
+    USE_PRECOMPILED_HEADER=0
+  endif
+  
+  ifeq ($(USE_PRECOMPILED_HEADER),1)
+  
+    ifndef LP64
+      $(error " Precompiled Headers only supported on 64-bit platforms!")
+    endif
+  
+    PRECOMPILED_HEADER_DIR=.
+    PRECOMPILED_HEADER_SRC=$(GAMMADIR)/src/share/vm/precompiled/precompiled.hpp
+    PRECOMPILED_HEADER=$(PRECOMPILED_HEADER_DIR)/precompiled.hpp.pch
+  
+    PCH_FLAG = -include precompiled.hpp
+    PCH_FLAG/DEFAULT = $(PCH_FLAG)
+    PCH_FLAG/NO_PCH = -DNO_PCH
+    PCH_FLAG/BY_FILE = $(PCH_FLAG/$@)$(PCH_FLAG/DEFAULT$(PCH_FLAG/$@))
+  
+    VM_PCH_FLAG/LIBJVM = $(PCH_FLAG/BY_FILE)
+    VM_PCH_FLAG/AOUT =
+    VM_PCH_FLAG = $(VM_PCH_FLAG/$(LINK_INTO))
+  
+    # We only use precompiled headers for the JVM build
+    CFLAGS += $(VM_PCH_FLAG)
+  
+    # There are some files which don't like precompiled headers
+    # The following files are build with 'OPT_CFLAGS/NOOPT' (-O0) in the opt build.
+    # But Clang doesn't support a precompiled header which was compiled with -O3
+    # to be used in a compilation unit which uses '-O0'. We could also prepare an
+    # extra '-O0' PCH file for the opt build and use it here, but it's probably
+    # not worth the effort as long as only two files need this special handling.
+    PCH_FLAG/loopTransform.o = $(PCH_FLAG/NO_PCH)
+    PCH_FLAG/sharedRuntimeTrig.o = $(PCH_FLAG/NO_PCH)
+    PCH_FLAG/sharedRuntimeTrans.o = $(PCH_FLAG/NO_PCH)
+  
+  endif
+else # ($(USE_CLANG), true)
+  # check for precompiled headers support
+  ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 3 \) \| \( \( $(CC_VER_MAJOR) = 3 \) \& \( $(CC_VER_MINOR) \>= 4 \) \))" "0"
+    # Allow the user to turn off precompiled headers from the command line.
+    ifneq ($(USE_PRECOMPILED_HEADER),0)
+      PRECOMPILED_HEADER_DIR=.
+      PRECOMPILED_HEADER_SRC=$(GAMMADIR)/src/share/vm/precompiled/precompiled.hpp
+      PRECOMPILED_HEADER=$(PRECOMPILED_HEADER_DIR)/precompiled.hpp.gch
+    endif
+  endif
 endif
 
+# -DDONT_USE_PRECOMPILED_HEADER will exclude all includes in precompiled.hpp.
+ifeq ($(USE_PRECOMPILED_HEADER),0)
+  CFLAGS += -DDONT_USE_PRECOMPILED_HEADER
+endif
 
 #------------------------------------------------------------------------
 # Compiler flags
@@ -115,17 +178,31 @@
 CFLAGS += $(VM_PICFLAG)
 CFLAGS += -fno-rtti
 CFLAGS += -fno-exceptions
-CFLAGS += -pthread
-CFLAGS += -fcheck-new
-# version 4 and above support fvisibility=hidden (matches jni_x86.h file)
-# except 4.1.2 gives pointless warnings that can't be disabled (afaik)
-ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
-CFLAGS += -fvisibility=hidden
+ifeq ($(USE_CLANG),)
+  CFLAGS += -pthread
+  CFLAGS += -fcheck-new
+  # version 4 and above support fvisibility=hidden (matches jni_x86.h file)
+  # except 4.1.2 gives pointless warnings that can't be disabled (afaik)
+  ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
+    CFLAGS += -fvisibility=hidden
+  endif
+else
+  CFLAGS += -fvisibility=hidden
+endif
+
+ifeq ($(USE_CLANG), true)
+  # Before Clang 3.1, we had to pass the stack alignment specification directly to llvm with the help of '-mllvm'
+  # Starting with version 3.1, Clang understands the '-mstack-alignment' (and rejects '-mllvm -stack-alignment')
+  ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 3 \) \| \( \( $(CC_VER_MAJOR) = 3 \) \& \( $(CC_VER_MINOR) \>= 1 \) \))" "0"
+    STACK_ALIGNMENT_OPT = -mno-omit-leaf-frame-pointer -mstack-alignment=16
+  else
+    STACK_ALIGNMENT_OPT = -mno-omit-leaf-frame-pointer -mllvm -stack-alignment=16
+  endif
 endif
 
 ARCHFLAG = $(ARCHFLAG/$(BUILDARCH))
 ARCHFLAG/i486    = -m32 -march=i586
-ARCHFLAG/amd64   = -m64
+ARCHFLAG/amd64   = -m64 $(STACK_ALIGNMENT_OPT)
 ARCHFLAG/ia64    =
 ARCHFLAG/sparc   = -m32 -mcpu=v9
 ARCHFLAG/sparcv9 = -m64 -mcpu=v9
@@ -163,14 +240,25 @@
   WARNINGS_ARE_ERRORS = -Werror
 endif
 
-# Except for a few acceptable ones
-# Since GCC 4.3, -Wconversion has changed its meanings to warn these implicit
-# conversions which might affect the values. To avoid that, we need to turn
-# it off explicitly. 
-ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
+ifeq ($(USE_CLANG), true)
+  # However we need to clean the code up before we can unrestrictedly enable this option with Clang
+  WARNINGS_ARE_ERRORS += -Wno-unused-value -Wno-logical-op-parentheses -Wno-parentheses-equality -Wno-parentheses
+  WARNINGS_ARE_ERRORS += -Wno-switch -Wno-tautological-compare
+# Not yet supported by clang in Xcode 4.6.2
+#  WARNINGS_ARE_ERRORS += -Wno-tautological-constant-out-of-range-compare
+  WARNINGS_ARE_ERRORS += -Wno-delete-non-virtual-dtor -Wno-deprecated -Wno-format -Wno-dynamic-class-memaccess
+  WARNINGS_ARE_ERRORS += -Wno-return-type -Wno-empty-body
+endif
+
 WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef
-else
-WARNING_FLAGS = -Wpointer-arith -Wconversion -Wsign-compare -Wundef
+
+ifeq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
+  # Since GCC 4.3, -Wconversion has changed its meanings to warn these implicit
+  # conversions which might affect the values. Only enable it in earlier versions.
+  WARNING_FLAGS = -Wunused-function
+  ifeq ($(USE_CLANG),)
+    WARNINGS_FLAGS += -Wconversion
+  endif
 endif
 
 CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(WARNING_FLAGS)
@@ -214,14 +302,24 @@
 
 OPT_CFLAGS/NOOPT=-O0
 
-# 6835796. Problem in GCC 4.3.0 with mulnode.o optimized compilation. 
-ifneq "$(shell expr \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) = 3 \) \))" "0"
-OPT_CFLAGS/mulnode.o += -O0
+# Work around some compiler bugs.
+ifeq ($(USE_CLANG), true)
+  ifeq ($(shell expr $(CC_VER_MAJOR) = 4 \& $(CC_VER_MINOR) = 2), 1)
+    OPT_CFLAGS/loopTransform.o += $(OPT_CFLAGS/NOOPT)
+  endif
+else
+  # 6835796. Problem in GCC 4.3.0 with mulnode.o optimized compilation.
+  ifeq ($(shell expr $(CC_VER_MAJOR) = 4 \& $(CC_VER_MINOR) = 3), 1)
+    OPT_CFLAGS/mulnode.o += $(OPT_CFLAGS/NOOPT)
+  endif
 endif
 
 # Flags for generating make dependency flags.
-ifneq ("${CC_VER_MAJOR}", "2")
-DEPFLAGS = -fpch-deps -MMD -MP -MF $(DEP_DIR)/$(@:%=%.d)
+DEPFLAGS = -MMD -MP -MF $(DEP_DIR)/$(@:%=%.d)
+ifeq ($(USE_CLANG),)
+  ifneq ($(CC_VER_MAJOR), 2)
+    DEPFLAGS += -fpch-deps
+  endif
 endif
 
 # -DDONT_USE_PRECOMPILED_HEADER will exclude all includes in precompiled.hpp.
@@ -249,13 +347,15 @@
 # statically link libstdc++.so, work with gcc but ignored by g++
 STATIC_STDCXX = -Wl,-Bstatic -lstdc++ -Wl,-Bdynamic
 
-# statically link libgcc and/or libgcc_s, libgcc does not exist before gcc-3.x.
-ifneq ("${CC_VER_MAJOR}", "2")
-STATIC_LIBGCC += -static-libgcc
-endif
+ifeq ($(USE_CLANG),)
+  # statically link libgcc and/or libgcc_s, libgcc does not exist before gcc-3.x.
+  ifneq ("${CC_VER_MAJOR}", "2")
+    STATIC_LIBGCC += -static-libgcc
+  endif
 
-ifeq ($(BUILDARCH), ia64)
-LFLAGS += -Wl,-relax
+  ifeq ($(BUILDARCH), ia64)
+    LFLAGS += -Wl,-relax
+  endif
 endif
 
 # Use $(MAPFLAG:FILENAME=real_file_name) to specify a map file.
@@ -296,25 +396,31 @@
 #------------------------------------------------------------------------
 # Debug flags
 
-# Use the stabs format for debugging information (this is the default
-# on gcc-2.91). It's good enough, has all the information about line
-# numbers and local variables, and libjvm.so is only about 16M.
-# Change this back to "-g" if you want the most expressive format.
-# (warning: that could easily inflate libjvm.so to 150M!)
-# Note: The Itanium gcc compiler crashes when using -gstabs.
-DEBUG_CFLAGS/ia64  = -g
-DEBUG_CFLAGS/amd64 = -g
-DEBUG_CFLAGS/arm   = -g
-DEBUG_CFLAGS/ppc   = -g
-DEBUG_CFLAGS += $(DEBUG_CFLAGS/$(BUILDARCH))
-ifeq ($(DEBUG_CFLAGS/$(BUILDARCH)),)
-DEBUG_CFLAGS += -gstabs
+ifeq ($(USE_CLANG), true)
+  # Restrict the debug information created by Clang to avoid
+  # too big object files and speed the build up a little bit
+  # (see http://llvm.org/bugs/show_bug.cgi?id=7554)
+  CFLAGS += -flimit-debug-info
 endif
 
-# DEBUG_BINARIES overrides everything, use full -g debug information
+# DEBUG_BINARIES uses full -g debug information for all configs
 ifeq ($(DEBUG_BINARIES), true)
-  DEBUG_CFLAGS = -g
-  CFLAGS += $(DEBUG_CFLAGS)
+  CFLAGS += -g
+else
+  # Use the stabs format for debugging information (this is the default
+  # on gcc-2.91). It's good enough, has all the information about line
+  # numbers and local variables, and libjvm.so is only about 16M.
+  # Change this back to "-g" if you want the most expressive format.
+  # (warning: that could easily inflate libjvm.so to 150M!)
+  # Note: The Itanium gcc compiler crashes when using -gstabs.
+  DEBUG_CFLAGS/ia64  = -g
+  DEBUG_CFLAGS/amd64 = -g
+  DEBUG_CFLAGS/arm   = -g
+  DEBUG_CFLAGS/ppc   = -g
+  DEBUG_CFLAGS += $(DEBUG_CFLAGS/$(BUILDARCH))
+  ifeq ($(DEBUG_CFLAGS/$(BUILDARCH)),)
+  DEBUG_CFLAGS += -gstabs
+  endif
 endif
 
 # If we are building HEADLESS, pass on to VM
--- old/make/bsd/makefiles/vm.make	2013-06-04 10:02:56.000000000 -0700
+++ new/make/bsd/makefiles/vm.make	2013-06-04 10:02:55.000000000 -0700
@@ -126,7 +126,11 @@
 LFLAGS += -Xlinker -z -Xlinker noexecstack
 endif
 
-LIBS += -lm -pthread
+LIBS += -lm
+
+ifeq ($(USE_CLANG),)
+  LIBS += -pthread
+endif
 
 # By default, link the *.o into the library, not the executable.
 LINK_INTO$(LINK_INTO) = LIBJVM
--- old/make/linux/makefiles/adlc.make	2013-06-04 10:03:19.000000000 -0700
+++ new/make/linux/makefiles/adlc.make	2013-06-04 10:03:18.000000000 -0700
@@ -68,7 +68,7 @@
 
 # CFLAGS_WARN holds compiler options to suppress/enable warnings.
 # Compiler warnings are treated as errors
-CFLAGS_WARN = -Werror
+CFLAGS_WARN = $(WARNINGS_ARE_ERRORS)
 CFLAGS += $(CFLAGS_WARN)
 
 OBJECTNAMES = \
--- old/make/linux/makefiles/gcc.make	2013-06-04 10:03:39.000000000 -0700
+++ new/make/linux/makefiles/gcc.make	2013-06-04 10:03:39.000000000 -0700
@@ -36,8 +36,14 @@
     HOSTCC  = gcc
     STRIP = $(ALT_COMPILER_PATH)/strip
   else
-    CXX = g++
-    CC  = gcc
+    ifeq ($(USE_CLANG), true)
+      CXX = clang++
+      CC  = clang
+    else
+      CXX = g++
+      CC  = gcc
+    endif
+
     HOSTCXX = $(CXX)
     HOSTCC  = $(CC)
     STRIP = strip
@@ -46,19 +52,79 @@
 endif
 
 
-# -dumpversion in gcc-2.91 shows "egcs-2.91.66". In later version, it only
-# prints the numbers (e.g. "2.95", "3.2.1")
-CC_VER_MAJOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f1)
-CC_VER_MINOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f2)
-
-# check for precompiled headers support
-ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 3 \) \| \( \( $(CC_VER_MAJOR) = 3 \) \& \( $(CC_VER_MINOR) \>= 4 \) \))" "0"
-# Allow the user to turn off precompiled headers from the command line.
-ifneq ($(USE_PRECOMPILED_HEADER),0)
-PRECOMPILED_HEADER_DIR=.
-PRECOMPILED_HEADER_SRC=$(GAMMADIR)/src/share/vm/precompiled/precompiled.hpp
-PRECOMPILED_HEADER=$(PRECOMPILED_HEADER_DIR)/precompiled.hpp.gch
+ifeq ($(USE_CLANG), true)
+  CC_VER_MAJOR := $(shell $(CC) -v 2>&1 | grep version | sed "s/.*version \([0-9]*\.[0-9]*\).*/\1/" | cut -d'.' -f1)
+  CC_VER_MINOR := $(shell $(CC) -v 2>&1 | grep version | sed "s/.*version \([0-9]*\.[0-9]*\).*/\1/" | cut -d'.' -f2)
+else
+  # -dumpversion in gcc-2.91 shows "egcs-2.91.66". In later version, it only
+  # prints the numbers (e.g. "2.95", "3.2.1")
+  CC_VER_MAJOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f1)
+  CC_VER_MINOR := $(shell $(CC) -dumpversion | sed 's/egcs-//' | cut -d'.' -f2)
 endif
+
+
+ifeq ($(USE_CLANG), true)
+  # Clang has precompiled headers support by default, but the user can switch
+  # it off by using 'USE_PRECOMPILED_HEADER=0'.
+  ifdef LP64
+    ifeq ($(USE_PRECOMPILED_HEADER),)
+      USE_PRECOMPILED_HEADER=1
+    endif
+  else
+    # We don't support precompiled headers on 32-bit builds because there some files are
+    # compiled with -fPIC while others are compiled without (see 'NONPIC_OBJ_FILES' rules.make)
+    # Clang produces an error if the PCH file was compiled with other options than the actual compilation unit.
+    USE_PRECOMPILED_HEADER=0
+  endif
+
+  ifeq ($(USE_PRECOMPILED_HEADER),1)
+
+    ifndef LP64
+      $(error " Precompiled Headers only supported on 64-bit platforms!")
+    endif
+
+    PRECOMPILED_HEADER_DIR=.
+    PRECOMPILED_HEADER_SRC=$(GAMMADIR)/src/share/vm/precompiled/precompiled.hpp
+    PRECOMPILED_HEADER=$(PRECOMPILED_HEADER_DIR)/precompiled.hpp.pch
+
+    PCH_FLAG = -include precompiled.hpp
+    PCH_FLAG/DEFAULT = $(PCH_FLAG)
+    PCH_FLAG/NO_PCH = -DNO_PCH
+    PCH_FLAG/BY_FILE = $(PCH_FLAG/$@)$(PCH_FLAG/DEFAULT$(PCH_FLAG/$@))
+
+    VM_PCH_FLAG/LIBJVM = $(PCH_FLAG/BY_FILE)
+    VM_PCH_FLAG/AOUT =
+    VM_PCH_FLAG = $(VM_PCH_FLAG/$(LINK_INTO))
+
+    # We only use precompiled headers for the JVM build
+    CFLAGS += $(VM_PCH_FLAG)
+
+    # There are some files which don't like precompiled headers
+    # The following files are build with 'OPT_CFLAGS/NOOPT' (-O0) in the opt build.
+    # But Clang doesn't support a precompiled header which was compiled with -O3
+    # to be used in a compilation unit which uses '-O0'. We could also prepare an
+    # extra '-O0' PCH file for the opt build and use it here, but it's probably
+    # not worth the effoert as long as only two files need this special handling.
+    PCH_FLAG/loopTransform.o = $(PCH_FLAG/NO_PCH)
+    PCH_FLAG/sharedRuntimeTrig.o = $(PCH_FLAG/NO_PCH)
+    PCH_FLAG/sharedRuntimeTrans.o = $(PCH_FLAG/NO_PCH)
+
+  endif
+else # ($(USE_CLANG), true)
+  # check for precompiled headers support
+  ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 3 \) \| \( \( $(CC_VER_MAJOR) = 3 \) \& \( $(CC_VER_MINOR) \>= 4 \) \))" "0"
+    # Allow the user to turn off precompiled headers from the command line.
+    ifneq ($(USE_PRECOMPILED_HEADER),0)
+      PRECOMPILED_HEADER_DIR=.
+      PRECOMPILED_HEADER_SRC=$(GAMMADIR)/src/share/vm/precompiled/precompiled.hpp
+      PRECOMPILED_HEADER=$(PRECOMPILED_HEADER_DIR)/precompiled.hpp.gch
+    endif
+  endif
+endif
+
+# -DDONT_USE_PRECOMPILED_HEADER will exclude all includes in precompiled.hpp.
+ifeq ($(USE_PRECOMPILED_HEADER),0)
+  CFLAGS += -DDONT_USE_PRECOMPILED_HEADER
 endif
 
 
@@ -83,16 +149,30 @@
 CFLAGS += -fno-rtti
 CFLAGS += -fno-exceptions
 CFLAGS += -D_REENTRANT
-CFLAGS += -fcheck-new
-# version 4 and above support fvisibility=hidden (matches jni_x86.h file)
-# except 4.1.2 gives pointless warnings that can't be disabled (afaik)
-ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
-CFLAGS += -fvisibility=hidden
+ifeq ($(USE_CLANG),)
+  CFLAGS += -fcheck-new
+  # version 4 and above support fvisibility=hidden (matches jni_x86.h file)
+  # except 4.1.2 gives pointless warnings that can't be disabled (afaik)
+  ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
+    CFLAGS += -fvisibility=hidden
+  endif
+else
+  CFLAGS += -fvisibility=hidden
+endif
+
+ifeq ($(USE_CLANG), true)
+  # Before Clang 3.1, we had to pass the stack alignment specification directly to llvm with the help of '-mllvm'
+  # Starting with version 3.1, Clang understands the '-mstack-alignment' (and rejects '-mllvm -stack-alignment')
+  ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 3 \) \| \( \( $(CC_VER_MAJOR) = 3 \) \& \( $(CC_VER_MINOR) \>= 1 \) \))" "0"
+    STACK_ALIGNMENT_OPT = -mno-omit-leaf-frame-pointer -mstack-alignment=16
+  else
+    STACK_ALIGNMENT_OPT = -mno-omit-leaf-frame-pointer -mllvm -stack-alignment=16
+  endif
 endif
 
 ARCHFLAG = $(ARCHFLAG/$(BUILDARCH))
 ARCHFLAG/i486    = -m32 -march=i586
-ARCHFLAG/amd64   = -m64
+ARCHFLAG/amd64   = -m64 $(STACK_ALIGNMENT_OPT)
 ARCHFLAG/ia64    =
 ARCHFLAG/sparc   = -m32 -mcpu=v9
 ARCHFLAG/sparcv9 = -m64 -mcpu=v9
@@ -126,12 +206,22 @@
 # Compiler warnings are treated as errors
 WARNINGS_ARE_ERRORS = -Werror
 
+ifeq ($(USE_CLANG), true)
+  # However we need to clean the code up before we can unrestrictedly enable this option with Clang
+  WARNINGS_ARE_ERRORS += -Wno-unused-value -Wno-logical-op-parentheses -Wno-parentheses-equality -Wno-parentheses
+  WARNINGS_ARE_ERRORS += -Wno-switch -Wno-tautological-constant-out-of-range-compare -Wno-tautological-compare
+  WARNINGS_ARE_ERRORS += -Wno-delete-non-virtual-dtor -Wno-deprecated -Wno-format -Wno-dynamic-class-memaccess
+  WARNINGS_ARE_ERRORS += -Wno-return-type -Wno-empty-body
+endif
+
 WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef -Wunused-function
 
-# Since GCC 4.3, -Wconversion has changed its meanings to warn these implicit
-# conversions which might affect the values. Only enable it in earlier versions.
-ifeq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
-WARNING_FLAGS += -Wconversion
+ifeq ($(USE_CLANG),)
+  # Since GCC 4.3, -Wconversion has changed its meanings to warn these implicit
+  # conversions which might affect the values. Only enable it in earlier versions.
+  ifeq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
+    WARNING_FLAGS += -Wconversion
+  endif
 endif
 
 CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(WARNING_FLAGS)
@@ -165,19 +255,24 @@
 
 OPT_CFLAGS/NOOPT=-O0
 
-# 6835796. Problem in GCC 4.3.0 with mulnode.o optimized compilation. 
-ifneq "$(shell expr \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) = 3 \) \))" "0"
-OPT_CFLAGS/mulnode.o += -O0
+# Work around some compiler bugs.
+ifeq ($(USE_CLANG), true)
+  ifeq ($(shell expr $(CC_VER_MAJOR) = 4 \& $(CC_VER_MINOR) = 2), 1)
+    OPT_CFLAGS/loopTransform.o += $(OPT_CFLAGS/NOOPT)
+  endif
+else
+  # 6835796. Problem in GCC 4.3.0 with mulnode.o optimized compilation.
+  ifeq ($(shell expr $(CC_VER_MAJOR) = 4 \& $(CC_VER_MINOR) = 3), 1)
+    OPT_CFLAGS/mulnode.o += $(OPT_CFLAGS/NOOPT)
+  endif
 endif
 
 # Flags for generating make dependency flags.
-ifneq ("${CC_VER_MAJOR}", "2")
-DEPFLAGS = -fpch-deps -MMD -MP -MF $(DEP_DIR)/$(@:%=%.d)
-endif
-
-# -DDONT_USE_PRECOMPILED_HEADER will exclude all includes in precompiled.hpp.
-ifeq ($(USE_PRECOMPILED_HEADER),0)
-CFLAGS += -DDONT_USE_PRECOMPILED_HEADER
+DEPFLAGS = -MMD -MP -MF $(DEP_DIR)/$(@:%=%.d)
+ifeq ($(USE_CLANG),)
+  ifneq ("${CC_VER_MAJOR}", "2")
+    DEPFLAGS += -fpch-deps
+  endif
 endif
 
 #------------------------------------------------------------------------
@@ -186,24 +281,33 @@
 # statically link libstdc++.so, work with gcc but ignored by g++
 STATIC_STDCXX = -Wl,-Bstatic -lstdc++ -Wl,-Bdynamic
 
-# statically link libgcc and/or libgcc_s, libgcc does not exist before gcc-3.x.
-ifneq ("${CC_VER_MAJOR}", "2")
-STATIC_LIBGCC += -static-libgcc
-endif
+ifeq ($(USE_CLANG),)
+  # statically link libgcc and/or libgcc_s, libgcc does not exist before gcc-3.x.
+  ifneq ("${CC_VER_MAJOR}", "2")
+    STATIC_LIBGCC += -static-libgcc
+  endif
 
-ifeq ($(BUILDARCH), ia64)
-LFLAGS += -Wl,-relax
+  ifeq ($(BUILDARCH), ia64)
+    LFLAGS += -Wl,-relax
+  endif
 endif
 
 # Enable linker optimization
 LFLAGS += -Xlinker -O1
 
-# If this is a --hash-style=gnu system, use --hash-style=both
-#   The gnu .hash section won't work on some Linux systems like SuSE 10.
-_HAS_HASH_STYLE_GNU:=$(shell $(CC) -dumpspecs | grep -- '--hash-style=gnu')
-ifneq ($(_HAS_HASH_STYLE_GNU),)
+ifeq ($(USE_CLANG),)
+  # If this is a --hash-style=gnu system, use --hash-style=both
+  #   The gnu .hash section won't work on some Linux systems like SuSE 10.
+  _HAS_HASH_STYLE_GNU:=$(shell $(CC) -dumpspecs | grep -- '--hash-style=gnu')
+  ifneq ($(_HAS_HASH_STYLE_GNU),)
+    LDFLAGS_HASH_STYLE = -Wl,--hash-style=both
+  endif
+else
+  # Don't know how to find out the 'hash style' of a system as '-dumpspecs'
+  # doesn't work for Clang. So for now we'll alwys use --hash-style=both
   LDFLAGS_HASH_STYLE = -Wl,--hash-style=both
 endif
+
 LFLAGS += $(LDFLAGS_HASH_STYLE)
 
 # Use $(MAPFLAG:FILENAME=real_file_name) to specify a map file.
@@ -221,6 +325,13 @@
 #------------------------------------------------------------------------
 # Debug flags
 
+ifeq ($(USE_CLANG), true)
+  # Restrict the debug information created by Clang to avoid
+  # too big object files and speed the build up a little bit
+  # (see http://llvm.org/bugs/show_bug.cgi?id=7554)
+  CFLAGS += -flimit-debug-info
+endif
+
 # DEBUG_BINARIES uses full -g debug information for all configs
 ifeq ($(DEBUG_BINARIES), true)
   CFLAGS += -g
@@ -237,7 +348,12 @@
   DEBUG_CFLAGS/ppc   = -g
   DEBUG_CFLAGS += $(DEBUG_CFLAGS/$(BUILDARCH))
   ifeq ($(DEBUG_CFLAGS/$(BUILDARCH)),)
-    DEBUG_CFLAGS += -gstabs
+      ifeq ($(USE_CLANG), true)
+        # Clang doesn't understand -gstabs
+        OPT_CFLAGS += -g
+      else
+        OPT_CFLAGS += -gstabs
+      endif
   endif
   
   ifeq ($(ENABLE_FULL_DEBUG_SYMBOLS),1)
@@ -247,7 +363,12 @@
     FASTDEBUG_CFLAGS/ppc   = -g
     FASTDEBUG_CFLAGS += $(DEBUG_CFLAGS/$(BUILDARCH))
     ifeq ($(FASTDEBUG_CFLAGS/$(BUILDARCH)),)
-      FASTDEBUG_CFLAGS += -gstabs
+      ifeq ($(USE_CLANG), true)
+        # Clang doesn't understand -gstabs
+        OPT_CFLAGS += -g
+      else
+        OPT_CFLAGS += -gstabs
+      endif
     endif
   
     OPT_CFLAGS/ia64  = -g
@@ -256,7 +377,12 @@
     OPT_CFLAGS/ppc   = -g
     OPT_CFLAGS += $(OPT_CFLAGS/$(BUILDARCH))
     ifeq ($(OPT_CFLAGS/$(BUILDARCH)),)
-      OPT_CFLAGS += -gstabs
+      ifeq ($(USE_CLANG), true)
+        # Clang doesn't understand -gstabs
+        OPT_CFLAGS += -g
+      else
+        OPT_CFLAGS += -gstabs
+      endif
     endif
   endif
 endif
--- old/src/os/bsd/vm/os_bsd.cpp	2013-06-04 10:04:06.000000000 -0700
+++ new/src/os/bsd/vm/os_bsd.cpp	2013-06-04 10:04:05.000000000 -0700
@@ -626,8 +626,6 @@
 //////////////////////////////////////////////////////////////////////////////
 // create new thread
 
-static address highest_vm_reserved_address();
-
 // check if it's safe to start a new thread
 static bool _thread_safety_check(Thread* thread) {
   return true;
@@ -2112,10 +2110,6 @@
   return anon_munmap(addr, size);
 }
 
-static address highest_vm_reserved_address() {
-  return _highest_vm_reserved_address;
-}
-
 static bool bsd_mprotect(char* addr, size_t size, int prot) {
   // Bsd wants the mprotect address argument to be page aligned.
   char* bottom = (char*)align_size_down((intptr_t)addr, os::Bsd::page_size());
@@ -2159,43 +2153,6 @@
   return false;
 }
 
-/*
-* Set the coredump_filter bits to include largepages in core dump (bit 6)
-*
-* From the coredump_filter documentation:
-*
-* - (bit 0) anonymous private memory
-* - (bit 1) anonymous shared memory
-* - (bit 2) file-backed private memory
-* - (bit 3) file-backed shared memory
-* - (bit 4) ELF header pages in file-backed private memory areas (it is
-*           effective only if the bit 2 is cleared)
-* - (bit 5) hugetlb private memory
-* - (bit 6) hugetlb shared memory
-*/
-static void set_coredump_filter(void) {
-  FILE *f;
-  long cdm;
-
-  if ((f = fopen("/proc/self/coredump_filter", "r+")) == NULL) {
-    return;
-  }
-
-  if (fscanf(f, "%lx", &cdm) != 1) {
-    fclose(f);
-    return;
-  }
-
-  rewind(f);
-
-  if ((cdm & LARGEPAGES_BIT) == 0) {
-    cdm |= LARGEPAGES_BIT;
-    fprintf(f, "%#lx", cdm);
-  }
-
-  fclose(f);
-}
-
 // Large page support
 
 static size_t _large_page_size = 0;
--- old/src/os_cpu/linux_x86/vm/linux_x86_32.s	2013-06-04 10:04:32.000000000 -0700
+++ new/src/os_cpu/linux_x86/vm/linux_x86_32.s	2013-06-04 10:04:31.000000000 -0700
@@ -241,7 +241,7 @@
         jbe      2f                   # <= 32 dwords
         rep;     smovl
         jmp      4f
-	.=.+8
+	.space 8
 2:      subl     %esi,%edi
         .p2align 4,,15
 3:      movl     (%esi),%edx
@@ -378,7 +378,7 @@
         rep;     smovl
         jmp      4f 
         # copy aligned dwords
-        .=.+5
+        .space 5
 2:      subl     %esi,%edi 
         .p2align 4,,15
 3:      movl     (%esi),%edx
@@ -454,7 +454,7 @@
         popl     %edi
         popl     %esi
         ret
-        .=.+10
+        .space 10
 2:      subl     %esi,%edi
         jmp      4f
         .p2align 4,,15
--- old/src/os_cpu/linux_x86/vm/os_linux_x86.cpp	2013-06-04 10:04:53.000000000 -0700
+++ new/src/os_cpu/linux_x86/vm/os_linux_x86.cpp	2013-06-04 10:04:53.000000000 -0700
@@ -93,6 +93,10 @@
   register void *esp;
   __asm__("mov %%"SPELL_REG_SP", %0":"=r"(esp));
   return (address) ((char*)esp + sizeof(long)*2);
+#elif defined(__clang__)
+  intptr_t* esp;
+  __asm__ __volatile__ ("mov %%"SPELL_REG_SP", %0":"=r"(esp):);
+  return (address) esp;
 #else
   register void *esp __asm__ (SPELL_REG_SP);
   return (address) esp;
@@ -175,6 +179,9 @@
 #ifdef SPARC_WORKS
   register intptr_t **ebp;
   __asm__("mov %%"SPELL_REG_FP", %0":"=r"(ebp));
+#elif defined(__clang__)
+  intptr_t **ebp;
+  __asm__ __volatile__ ("mov %%"SPELL_REG_FP", %0":"=r"(ebp):);
 #else
   register intptr_t **ebp __asm__ (SPELL_REG_FP);
 #endif