diff --git a/Makefile.rules b/Makefile.rules
index 4117169f3a3..3e577bbcf0f 100644
--- a/Makefile.rules
+++ b/Makefile.rules
@@ -200,7 +200,11 @@ install-bytecode:: install-bytecode-local
 
 # OPTIMIZE_OPTION - The optimization level option we want to build LLVM with
 # this can be overridden on the make command line.
-OPTIMIZE_OPTION := -O3
+ifneq ($(OS),MingW)
+  OPTIMIZE_OPTION := -O3
+else
+  OPTIMIZE_OPTION := -O2
+endif
 
 ifdef ENABLE_PROFILING
   BuildMode := Profile
diff --git a/autoconf/configure.ac b/autoconf/configure.ac
index c827ec7ecd3..2c2f2ce78e8 100644
--- a/autoconf/configure.ac
+++ b/autoconf/configure.ac
@@ -487,10 +487,8 @@ dnl libelf is for sparc only; we can ignore it if we don't have it
 AC_CHECK_LIB(elf, elf_begin)
 AC_CHECK_LIB(m,sin)
 if test "$llvm_cv_os_type" == "MingW" ; then
-  AC_CHECK_HEADERS([windows.h])
-  AC_CHECK_HEADERS([imagehlp.h psapi.h])
-  AC_CHECK_LIB(imagehlp,[SymGetOptions])
-  AC_CHECK_LIB(psapi,[GetProcessMemoryInfo])
+  AC_CHECK_LIB(imagehlp, main)
+  AC_CHECK_LIB(psapi, main)
 fi
 
 dnl lt_dlopen may be required for plugin support.
diff --git a/configure b/configure
index f5f3925a888..976ad445194 100755
--- a/configure
+++ b/configure
@@ -25147,310 +25147,9 @@ fi
 
 if test "$llvm_cv_os_type" == "MingW" ; then
 
-for ac_header in windows.h
-do
-as_ac_Header=`echo "ac_cv_header_$ac_header" | $as_tr_sh`
-if eval "test \"\${$as_ac_Header+set}\" = set"; then
-  echo "$as_me:$LINENO: checking for $ac_header" >&5
-echo $ECHO_N "checking for $ac_header... $ECHO_C" >&6
-if eval "test \"\${$as_ac_Header+set}\" = set"; then
-  echo $ECHO_N "(cached) $ECHO_C" >&6
-fi
-echo "$as_me:$LINENO: result: `eval echo '${'$as_ac_Header'}'`" >&5
-echo "${ECHO_T}`eval echo '${'$as_ac_Header'}'`" >&6
-else
-  # Is the header compilable?
-echo "$as_me:$LINENO: checking $ac_header usability" >&5
-echo $ECHO_N "checking $ac_header usability... $ECHO_C" >&6
-cat >conftest.$ac_ext <<_ACEOF
-/* confdefs.h.  */
-_ACEOF
-cat confdefs.h >>conftest.$ac_ext
-cat >>conftest.$ac_ext <<_ACEOF
-/* end confdefs.h.  */
-$ac_includes_default
-#include <$ac_header>
-_ACEOF
-rm -f conftest.$ac_objext
-if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
-  (eval $ac_compile) 2>conftest.er1
-  ac_status=$?
-  grep -v '^ *+' conftest.er1 >conftest.err
-  rm -f conftest.er1
-  cat conftest.err >&5
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); } &&
-	 { ac_try='test -z "$ac_c_werror_flag"
-			 || test ! -s conftest.err'
-  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
-  (eval $ac_try) 2>&5
-  ac_status=$?
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); }; } &&
-	 { ac_try='test -s conftest.$ac_objext'
-  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
-  (eval $ac_try) 2>&5
-  ac_status=$?
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); }; }; then
-  ac_header_compiler=yes
-else
-  echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
-
-ac_header_compiler=no
-fi
-rm -f conftest.err conftest.$ac_objext conftest.$ac_ext
-echo "$as_me:$LINENO: result: $ac_header_compiler" >&5
-echo "${ECHO_T}$ac_header_compiler" >&6
-
-# Is the header present?
-echo "$as_me:$LINENO: checking $ac_header presence" >&5
-echo $ECHO_N "checking $ac_header presence... $ECHO_C" >&6
-cat >conftest.$ac_ext <<_ACEOF
-/* confdefs.h.  */
-_ACEOF
-cat confdefs.h >>conftest.$ac_ext
-cat >>conftest.$ac_ext <<_ACEOF
-/* end confdefs.h.  */
-#include <$ac_header>
-_ACEOF
-if { (eval echo "$as_me:$LINENO: \"$ac_cpp conftest.$ac_ext\"") >&5
-  (eval $ac_cpp conftest.$ac_ext) 2>conftest.er1
-  ac_status=$?
-  grep -v '^ *+' conftest.er1 >conftest.err
-  rm -f conftest.er1
-  cat conftest.err >&5
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); } >/dev/null; then
-  if test -s conftest.err; then
-    ac_cpp_err=$ac_c_preproc_warn_flag
-    ac_cpp_err=$ac_cpp_err$ac_c_werror_flag
-  else
-    ac_cpp_err=
-  fi
-else
-  ac_cpp_err=yes
-fi
-if test -z "$ac_cpp_err"; then
-  ac_header_preproc=yes
-else
-  echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
-
-  ac_header_preproc=no
-fi
-rm -f conftest.err conftest.$ac_ext
-echo "$as_me:$LINENO: result: $ac_header_preproc" >&5
-echo "${ECHO_T}$ac_header_preproc" >&6
-
-# So?  What about this header?
-case $ac_header_compiler:$ac_header_preproc:$ac_c_preproc_warn_flag in
-  yes:no: )
-    { echo "$as_me:$LINENO: WARNING: $ac_header: accepted by the compiler, rejected by the preprocessor!" >&5
-echo "$as_me: WARNING: $ac_header: accepted by the compiler, rejected by the preprocessor!" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: proceeding with the compiler's result" >&5
-echo "$as_me: WARNING: $ac_header: proceeding with the compiler's result" >&2;}
-    ac_header_preproc=yes
-    ;;
-  no:yes:* )
-    { echo "$as_me:$LINENO: WARNING: $ac_header: present but cannot be compiled" >&5
-echo "$as_me: WARNING: $ac_header: present but cannot be compiled" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header:     check for missing prerequisite headers?" >&5
-echo "$as_me: WARNING: $ac_header:     check for missing prerequisite headers?" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: see the Autoconf documentation" >&5
-echo "$as_me: WARNING: $ac_header: see the Autoconf documentation" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header:     section \"Present But Cannot Be Compiled\"" >&5
-echo "$as_me: WARNING: $ac_header:     section \"Present But Cannot Be Compiled\"" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: proceeding with the preprocessor's result" >&5
-echo "$as_me: WARNING: $ac_header: proceeding with the preprocessor's result" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: in the future, the compiler will take precedence" >&5
-echo "$as_me: WARNING: $ac_header: in the future, the compiler will take precedence" >&2;}
-    (
-      cat <<\_ASBOX
-## ----------------------------------- ##
-## Report this to llvmbugs@cs.uiuc.edu ##
-## ----------------------------------- ##
-_ASBOX
-    ) |
-      sed "s/^/$as_me: WARNING:     /" >&2
-    ;;
-esac
-echo "$as_me:$LINENO: checking for $ac_header" >&5
-echo $ECHO_N "checking for $ac_header... $ECHO_C" >&6
-if eval "test \"\${$as_ac_Header+set}\" = set"; then
-  echo $ECHO_N "(cached) $ECHO_C" >&6
-else
-  eval "$as_ac_Header=\$ac_header_preproc"
-fi
-echo "$as_me:$LINENO: result: `eval echo '${'$as_ac_Header'}'`" >&5
-echo "${ECHO_T}`eval echo '${'$as_ac_Header'}'`" >&6
-
-fi
-if test `eval echo '${'$as_ac_Header'}'` = yes; then
-  cat >>confdefs.h <<_ACEOF
-#define `echo "HAVE_$ac_header" | $as_tr_cpp` 1
-_ACEOF
-
-fi
-
-done
-
-
-
-for ac_header in imagehlp.h psapi.h
-do
-as_ac_Header=`echo "ac_cv_header_$ac_header" | $as_tr_sh`
-if eval "test \"\${$as_ac_Header+set}\" = set"; then
-  echo "$as_me:$LINENO: checking for $ac_header" >&5
-echo $ECHO_N "checking for $ac_header... $ECHO_C" >&6
-if eval "test \"\${$as_ac_Header+set}\" = set"; then
-  echo $ECHO_N "(cached) $ECHO_C" >&6
-fi
-echo "$as_me:$LINENO: result: `eval echo '${'$as_ac_Header'}'`" >&5
-echo "${ECHO_T}`eval echo '${'$as_ac_Header'}'`" >&6
-else
-  # Is the header compilable?
-echo "$as_me:$LINENO: checking $ac_header usability" >&5
-echo $ECHO_N "checking $ac_header usability... $ECHO_C" >&6
-cat >conftest.$ac_ext <<_ACEOF
-/* confdefs.h.  */
-_ACEOF
-cat confdefs.h >>conftest.$ac_ext
-cat >>conftest.$ac_ext <<_ACEOF
-/* end confdefs.h.  */
-$ac_includes_default
-#include <$ac_header>
-_ACEOF
-rm -f conftest.$ac_objext
-if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
-  (eval $ac_compile) 2>conftest.er1
-  ac_status=$?
-  grep -v '^ *+' conftest.er1 >conftest.err
-  rm -f conftest.er1
-  cat conftest.err >&5
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); } &&
-	 { ac_try='test -z "$ac_c_werror_flag"
-			 || test ! -s conftest.err'
-  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
-  (eval $ac_try) 2>&5
-  ac_status=$?
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); }; } &&
-	 { ac_try='test -s conftest.$ac_objext'
-  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
-  (eval $ac_try) 2>&5
-  ac_status=$?
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); }; }; then
-  ac_header_compiler=yes
-else
-  echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
-
-ac_header_compiler=no
-fi
-rm -f conftest.err conftest.$ac_objext conftest.$ac_ext
-echo "$as_me:$LINENO: result: $ac_header_compiler" >&5
-echo "${ECHO_T}$ac_header_compiler" >&6
-
-# Is the header present?
-echo "$as_me:$LINENO: checking $ac_header presence" >&5
-echo $ECHO_N "checking $ac_header presence... $ECHO_C" >&6
-cat >conftest.$ac_ext <<_ACEOF
-/* confdefs.h.  */
-_ACEOF
-cat confdefs.h >>conftest.$ac_ext
-cat >>conftest.$ac_ext <<_ACEOF
-/* end confdefs.h.  */
-#include <$ac_header>
-_ACEOF
-if { (eval echo "$as_me:$LINENO: \"$ac_cpp conftest.$ac_ext\"") >&5
-  (eval $ac_cpp conftest.$ac_ext) 2>conftest.er1
-  ac_status=$?
-  grep -v '^ *+' conftest.er1 >conftest.err
-  rm -f conftest.er1
-  cat conftest.err >&5
-  echo "$as_me:$LINENO: \$? = $ac_status" >&5
-  (exit $ac_status); } >/dev/null; then
-  if test -s conftest.err; then
-    ac_cpp_err=$ac_c_preproc_warn_flag
-    ac_cpp_err=$ac_cpp_err$ac_c_werror_flag
-  else
-    ac_cpp_err=
-  fi
-else
-  ac_cpp_err=yes
-fi
-if test -z "$ac_cpp_err"; then
-  ac_header_preproc=yes
-else
-  echo "$as_me: failed program was:" >&5
-sed 's/^/| /' conftest.$ac_ext >&5
-
-  ac_header_preproc=no
-fi
-rm -f conftest.err conftest.$ac_ext
-echo "$as_me:$LINENO: result: $ac_header_preproc" >&5
-echo "${ECHO_T}$ac_header_preproc" >&6
-
-# So?  What about this header?
-case $ac_header_compiler:$ac_header_preproc:$ac_c_preproc_warn_flag in
-  yes:no: )
-    { echo "$as_me:$LINENO: WARNING: $ac_header: accepted by the compiler, rejected by the preprocessor!" >&5
-echo "$as_me: WARNING: $ac_header: accepted by the compiler, rejected by the preprocessor!" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: proceeding with the compiler's result" >&5
-echo "$as_me: WARNING: $ac_header: proceeding with the compiler's result" >&2;}
-    ac_header_preproc=yes
-    ;;
-  no:yes:* )
-    { echo "$as_me:$LINENO: WARNING: $ac_header: present but cannot be compiled" >&5
-echo "$as_me: WARNING: $ac_header: present but cannot be compiled" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header:     check for missing prerequisite headers?" >&5
-echo "$as_me: WARNING: $ac_header:     check for missing prerequisite headers?" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: see the Autoconf documentation" >&5
-echo "$as_me: WARNING: $ac_header: see the Autoconf documentation" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header:     section \"Present But Cannot Be Compiled\"" >&5
-echo "$as_me: WARNING: $ac_header:     section \"Present But Cannot Be Compiled\"" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: proceeding with the preprocessor's result" >&5
-echo "$as_me: WARNING: $ac_header: proceeding with the preprocessor's result" >&2;}
-    { echo "$as_me:$LINENO: WARNING: $ac_header: in the future, the compiler will take precedence" >&5
-echo "$as_me: WARNING: $ac_header: in the future, the compiler will take precedence" >&2;}
-    (
-      cat <<\_ASBOX
-## ----------------------------------- ##
-## Report this to llvmbugs@cs.uiuc.edu ##
-## ----------------------------------- ##
-_ASBOX
-    ) |
-      sed "s/^/$as_me: WARNING:     /" >&2
-    ;;
-esac
-echo "$as_me:$LINENO: checking for $ac_header" >&5
-echo $ECHO_N "checking for $ac_header... $ECHO_C" >&6
-if eval "test \"\${$as_ac_Header+set}\" = set"; then
-  echo $ECHO_N "(cached) $ECHO_C" >&6
-else
-  eval "$as_ac_Header=\$ac_header_preproc"
-fi
-echo "$as_me:$LINENO: result: `eval echo '${'$as_ac_Header'}'`" >&5
-echo "${ECHO_T}`eval echo '${'$as_ac_Header'}'`" >&6
-
-fi
-if test `eval echo '${'$as_ac_Header'}'` = yes; then
-  cat >>confdefs.h <<_ACEOF
-#define `echo "HAVE_$ac_header" | $as_tr_cpp` 1
-_ACEOF
-
-fi
-
-done
-
-
-echo "$as_me:$LINENO: checking for SymGetOptions in -limagehlp" >&5
-echo $ECHO_N "checking for SymGetOptions in -limagehlp... $ECHO_C" >&6
-if test "${ac_cv_lib_imagehlp_SymGetOptions+set}" = set; then
+echo "$as_me:$LINENO: checking for main in -limagehlp" >&5
+echo $ECHO_N "checking for main in -limagehlp... $ECHO_C" >&6
+if test "${ac_cv_lib_imagehlp_main+set}" = set; then
   echo $ECHO_N "(cached) $ECHO_C" >&6
 else
   ac_check_lib_save_LIBS=$LIBS
@@ -25462,17 +25161,11 @@ cat confdefs.h >>conftest.$ac_ext
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 
-/* Override any gcc2 internal prototype to avoid an error.  */
-#ifdef __cplusplus
-extern "C"
-#endif
-/* We use char because int might match the return type of a gcc2
-   builtin and then its argument prototype would still apply.  */
-char SymGetOptions ();
+
 int
 main ()
 {
-SymGetOptions ();
+main ();
   ;
   return 0;
 }
@@ -25499,20 +25192,20 @@ if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
   ac_status=$?
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
-  ac_cv_lib_imagehlp_SymGetOptions=yes
+  ac_cv_lib_imagehlp_main=yes
 else
   echo "$as_me: failed program was:" >&5
 sed 's/^/| /' conftest.$ac_ext >&5
 
-ac_cv_lib_imagehlp_SymGetOptions=no
+ac_cv_lib_imagehlp_main=no
 fi
 rm -f conftest.err conftest.$ac_objext \
       conftest$ac_exeext conftest.$ac_ext
 LIBS=$ac_check_lib_save_LIBS
 fi
-echo "$as_me:$LINENO: result: $ac_cv_lib_imagehlp_SymGetOptions" >&5
-echo "${ECHO_T}$ac_cv_lib_imagehlp_SymGetOptions" >&6
-if test $ac_cv_lib_imagehlp_SymGetOptions = yes; then
+echo "$as_me:$LINENO: result: $ac_cv_lib_imagehlp_main" >&5
+echo "${ECHO_T}$ac_cv_lib_imagehlp_main" >&6
+if test $ac_cv_lib_imagehlp_main = yes; then
   cat >>confdefs.h <<_ACEOF
 #define HAVE_LIBIMAGEHLP 1
 _ACEOF
@@ -25522,9 +25215,9 @@ _ACEOF
 fi
 
 
-echo "$as_me:$LINENO: checking for GetProcessMemoryInfo in -lpsapi" >&5
-echo $ECHO_N "checking for GetProcessMemoryInfo in -lpsapi... $ECHO_C" >&6
-if test "${ac_cv_lib_psapi_GetProcessMemoryInfo+set}" = set; then
+echo "$as_me:$LINENO: checking for main in -lpsapi" >&5
+echo $ECHO_N "checking for main in -lpsapi... $ECHO_C" >&6
+if test "${ac_cv_lib_psapi_main+set}" = set; then
   echo $ECHO_N "(cached) $ECHO_C" >&6
 else
   ac_check_lib_save_LIBS=$LIBS
@@ -25536,17 +25229,11 @@ cat confdefs.h >>conftest.$ac_ext
 cat >>conftest.$ac_ext <<_ACEOF
 /* end confdefs.h.  */
 
-/* Override any gcc2 internal prototype to avoid an error.  */
-#ifdef __cplusplus
-extern "C"
-#endif
-/* We use char because int might match the return type of a gcc2
-   builtin and then its argument prototype would still apply.  */
-char GetProcessMemoryInfo ();
+
 int
 main ()
 {
-GetProcessMemoryInfo ();
+main ();
   ;
   return 0;
 }
@@ -25573,20 +25260,20 @@ if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
   ac_status=$?
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
-  ac_cv_lib_psapi_GetProcessMemoryInfo=yes
+  ac_cv_lib_psapi_main=yes
 else
   echo "$as_me: failed program was:" >&5
 sed 's/^/| /' conftest.$ac_ext >&5
 
-ac_cv_lib_psapi_GetProcessMemoryInfo=no
+ac_cv_lib_psapi_main=no
 fi
 rm -f conftest.err conftest.$ac_objext \
       conftest$ac_exeext conftest.$ac_ext
 LIBS=$ac_check_lib_save_LIBS
 fi
-echo "$as_me:$LINENO: result: $ac_cv_lib_psapi_GetProcessMemoryInfo" >&5
-echo "${ECHO_T}$ac_cv_lib_psapi_GetProcessMemoryInfo" >&6
-if test $ac_cv_lib_psapi_GetProcessMemoryInfo = yes; then
+echo "$as_me:$LINENO: result: $ac_cv_lib_psapi_main" >&5
+echo "${ECHO_T}$ac_cv_lib_psapi_main" >&6
+if test $ac_cv_lib_psapi_main = yes; then
   cat >>confdefs.h <<_ACEOF
 #define HAVE_LIBPSAPI 1
 _ACEOF
diff --git a/lib/System/Win32/DynamicLibrary.inc b/lib/System/Win32/DynamicLibrary.inc
index 310d3dc8359..d214ba0e727 100644
--- a/lib/System/Win32/DynamicLibrary.inc
+++ b/lib/System/Win32/DynamicLibrary.inc
@@ -14,12 +14,18 @@
 #include "Win32.h"
 
 #ifdef __MINGW32__
-#include <imagehlp.h>
+ #include <imagehlp.h>
 #else
-#include <dbghelp.h>
+ #include <dbghelp.h>
 #endif
 
-#pragma comment(lib, "dbghelp.lib")
+#ifdef __MINGW32__
+ #if (HAVE_LIBIMAGEHLP != 1)
+  #error "libimagehlp.a should be present"
+ #endif
+#else
+ #pragma comment(lib, "dbghelp.lib")
+#endif
 
 namespace llvm {
 using namespace sys;
diff --git a/lib/System/Win32/Process.inc b/lib/System/Win32/Process.inc
index 5b090da3c2e..d5e80b4f19c 100644
--- a/lib/System/Win32/Process.inc
+++ b/lib/System/Win32/Process.inc
@@ -16,7 +16,13 @@
 #include <malloc.h>
 #include <io.h>
 
-#pragma comment(lib, "psapi.lib")
+#ifdef __MINGW32__
+ #if (HAVE_LIBPSAPI != 1)
+  #error "libpsapi.a should be present"
+ #endif
+#else
+ #pragma comment(lib, "psapi.lib")
+#endif
 
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only Win32 specific code 
diff --git a/lib/System/Win32/Signals.inc b/lib/System/Win32/Signals.inc
index 333e387dea1..a44c034ba1d 100644
--- a/lib/System/Win32/Signals.inc
+++ b/lib/System/Win32/Signals.inc
@@ -16,14 +16,20 @@
 #include <vector>
 
 #ifdef __MINGW32__
-#include <imagehlp.h>
+ #include <imagehlp.h>
 #else
-#include <dbghelp.h>
+ #include <dbghelp.h>
 #endif
 #include <psapi.h>
 
-#pragma comment(lib, "psapi.lib")
-#pragma comment(lib, "dbghelp.lib")
+#ifdef __MINGW32__
+ #if ((HAVE_LIBIMAGEHLP != 1) || (HAVE_LIBPSAPI != 1))
+  #error "libimagehlp.a & libpsapi.a should be present"
+ #endif
+#else
+ #pragma comment(lib, "psapi.lib")
+ #pragma comment(lib, "dbghelp.lib")
+#endif
 
 // Forward declare.
 static LONG WINAPI LLVMUnhandledExceptionFilter(LPEXCEPTION_POINTERS ep);