8344607: Link Time Optimization - basic support for clang

Reviewed-by: lucy, jkern, ihse

Author: MBaesken

make/hotspot/lib/JvmFeatures.gmk

@@ -174,6 +174,12 @@ ifeq ($(call check-jvm-feature, link-time-opt), true)
         -fno-fat-lto-objects
     JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM) -flto=auto \
         -fuse-linker-plugin -fno-strict-aliasing
+  else ifeq ($(call isCompiler, clang), true)
+    JVM_CFLAGS_FEATURES += -flto -fno-strict-aliasing
+    ifeq ($(call isBuildOs, aix), true)
+      JVM_CFLAGS_FEATURES += -ffat-lto-objects
+    endif
+    JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM) -flto -fno-strict-aliasing
   else ifeq ($(call isCompiler, microsoft), true)
     JVM_CFLAGS_FEATURES += -GL
     JVM_LDFLAGS_FEATURES += -LTCG:INCREMENTAL

src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp

@@ -501,6 +501,7 @@ static inline void atomic_copy64(const volatile void *src, volatile void *dst) {
 }
 
 extern "C" {
+  // needs local assembler label '1:' to avoid trouble when using linktime optimization
   int SpinPause() {
     // We don't use StubRoutines::aarch64::spin_wait stub in order to
     // avoid a costly call to os::current_thread_enable_wx() on MacOS.
@@ -523,14 +524,14 @@ extern "C" {
                                       // to entry for case SpinWait::NOP
         "  add  %[d], %[d], %[o]  \n"
         "  br   %[d]              \n"
-        "  b    SpinPause_return  \n" // case SpinWait::NONE  (-1)
+        "  b    1f                \n" // case SpinWait::NONE  (-1)
         "  nop                    \n" // padding
         "  nop                    \n" // case SpinWait::NOP   ( 0)
-        "  b    SpinPause_return  \n"
+        "  b    1f                \n"
         "  isb                    \n" // case SpinWait::ISB   ( 1)
-        "  b    SpinPause_return  \n"
+        "  b    1f                \n"
         "  yield                  \n" // case SpinWait::YIELD ( 2)
-        "SpinPause_return:        \n"
+        "1:        \n"
         : [d]"=&r"(br_dst)
         : [o]"r"(off)
         : "memory");