8370438: Offer link time optimization support on library level

Reviewed-by: erikj, serb, azvegint

make/autoconf/flags-cflags.m4

@@ -282,10 +282,17 @@ AC_DEFUN([FLAGS_SETUP_OPTIMIZATION],
     C_O_FLAG_DEBUG_JVM="-O0"
     C_O_FLAG_NONE="-O0"
 
+    if test "x$TOOLCHAIN_TYPE" = xgcc; then
+      C_O_FLAG_LTO="-flto=auto -fuse-linker-plugin -fno-strict-aliasing -fno-fat-lto-objects"
+    else
+      C_O_FLAG_LTO="-flto -fno-strict-aliasing"
+    fi
+
     if test "x$TOOLCHAIN_TYPE" = xclang && test "x$OPENJDK_TARGET_OS" = xaix; then
       C_O_FLAG_HIGHEST_JVM="${C_O_FLAG_HIGHEST_JVM} -finline-functions"
       C_O_FLAG_HIGHEST="${C_O_FLAG_HIGHEST} -finline-functions"
       C_O_FLAG_HI="${C_O_FLAG_HI} -finline-functions"
+      C_O_FLAG_LTO="${C_O_FLAG_LTO} -ffat-lto-objects"
     fi
 
     # -D_FORTIFY_SOURCE=2 hardening option needs optimization (at least -O1) enabled
@@ -317,6 +324,7 @@ AC_DEFUN([FLAGS_SETUP_OPTIMIZATION],
     C_O_FLAG_DEBUG_JVM=""
     C_O_FLAG_NONE="-Od"
     C_O_FLAG_SIZE="-O1"
+    C_O_FLAG_LTO="-GL"
   fi
 
   # Now copy to C++ flags
@@ -328,6 +336,7 @@ AC_DEFUN([FLAGS_SETUP_OPTIMIZATION],
   CXX_O_FLAG_DEBUG_JVM="$C_O_FLAG_DEBUG_JVM"
   CXX_O_FLAG_NONE="$C_O_FLAG_NONE"
   CXX_O_FLAG_SIZE="$C_O_FLAG_SIZE"
+  CXX_O_FLAG_LTO="$C_O_FLAG_LTO"
 
   # Adjust optimization flags according to debug level.
   case $DEBUG_LEVEL in
@@ -360,12 +369,15 @@ AC_DEFUN([FLAGS_SETUP_OPTIMIZATION],
   AC_SUBST(C_O_FLAG_NORM)
   AC_SUBST(C_O_FLAG_NONE)
   AC_SUBST(C_O_FLAG_SIZE)
+  AC_SUBST(C_O_FLAG_LTO)
+
   AC_SUBST(CXX_O_FLAG_HIGHEST_JVM)
   AC_SUBST(CXX_O_FLAG_HIGHEST)
   AC_SUBST(CXX_O_FLAG_HI)
   AC_SUBST(CXX_O_FLAG_NORM)
   AC_SUBST(CXX_O_FLAG_NONE)
   AC_SUBST(CXX_O_FLAG_SIZE)
+  AC_SUBST(CXX_O_FLAG_LTO)
 ])
 
 AC_DEFUN([FLAGS_SETUP_CFLAGS],

make/autoconf/flags-ldflags.m4

@@ -61,6 +61,7 @@ AC_DEFUN([FLAGS_SETUP_LDFLAGS_HELPER],
     fi
 
     BASIC_LDFLAGS_JVM_ONLY=""
+    LDFLAGS_LTO="-flto=auto -fuse-linker-plugin -fno-strict-aliasing"
 
     LDFLAGS_CXX_PARTIAL_LINKING="$MACHINE_FLAG -r"
 
@@ -68,6 +69,7 @@ AC_DEFUN([FLAGS_SETUP_LDFLAGS_HELPER],
     BASIC_LDFLAGS_JVM_ONLY="-mno-omit-leaf-frame-pointer -mstack-alignment=16 \
         -fPIC"
 
+    LDFLAGS_LTO="-flto=auto -fuse-linker-plugin -fno-strict-aliasing"
     LDFLAGS_CXX_PARTIAL_LINKING="$MACHINE_FLAG -r"
 
     if test "x$OPENJDK_TARGET_OS" = xlinux; then
@@ -87,6 +89,7 @@ AC_DEFUN([FLAGS_SETUP_LDFLAGS_HELPER],
     BASIC_LDFLAGS="-opt:ref"
     BASIC_LDFLAGS_JDK_ONLY="-incremental:no"
     BASIC_LDFLAGS_JVM_ONLY="-opt:icf,8 -subsystem:windows"
+    LDFLAGS_LTO="-LTCG:INCREMENTAL"
   fi
 
   if (test "x$TOOLCHAIN_TYPE" = xgcc || test "x$TOOLCHAIN_TYPE" = xclang) \
@@ -148,6 +151,7 @@ AC_DEFUN([FLAGS_SETUP_LDFLAGS_HELPER],
 
   # Export some intermediate variables for compatibility
   LDFLAGS_CXX_JDK="$DEBUGLEVEL_LDFLAGS_JDK_ONLY"
+  AC_SUBST(LDFLAGS_LTO)
   AC_SUBST(LDFLAGS_CXX_JDK)
   AC_SUBST(LDFLAGS_CXX_PARTIAL_LINKING)
 ])

make/autoconf/spec.gmk.template

@@ -513,12 +513,14 @@ C_O_FLAG_HI := @C_O_FLAG_HI@
 C_O_FLAG_NORM := @C_O_FLAG_NORM@
 C_O_FLAG_NONE := @C_O_FLAG_NONE@
 C_O_FLAG_SIZE := @C_O_FLAG_SIZE@
+C_O_FLAG_LTO := @C_O_FLAG_LTO@
 CXX_O_FLAG_HIGHEST_JVM := @CXX_O_FLAG_HIGHEST_JVM@
 CXX_O_FLAG_HIGHEST := @CXX_O_FLAG_HIGHEST@
 CXX_O_FLAG_HI := @CXX_O_FLAG_HI@
 CXX_O_FLAG_NORM := @CXX_O_FLAG_NORM@
 CXX_O_FLAG_NONE := @CXX_O_FLAG_NONE@
 CXX_O_FLAG_SIZE := @CXX_O_FLAG_SIZE@
+CXX_O_FLAG_LTO  := @CXX_O_FLAG_LTO@
 
 GENDEPS_FLAGS := @GENDEPS_FLAGS@
 
@@ -587,6 +589,9 @@ LDFLAGS_CXX_JDK := @LDFLAGS_CXX_JDK@
 # LDFLAGS specific to partial linking.
 LDFLAGS_CXX_PARTIAL_LINKING := @LDFLAGS_CXX_PARTIAL_LINKING@
 
+# LDFLAGS specific to link time optimization
+LDFLAGS_LTO := @LDFLAGS_LTO@
+
 # Sometimes a different linker is needed for c++ libs
 LDCXX := @LDCXX@
 # The flags for linking libstdc++ linker.

make/common/NativeCompilation.gmk

@@ -98,6 +98,7 @@ include native/Paths.gmk
 #   SYSROOT_CFLAGS the compiler flags for using the specific sysroot
 #   SYSROOT_LDFLAGS the linker flags for using the specific sysroot
 #   OPTIMIZATION sets optimization level to NONE, LOW, HIGH, HIGHEST, HIGHEST_JVM, SIZE
+#   LINK_TIME_OPTIMIZATION if set to true, enables link time optimization
 #   DISABLED_WARNINGS_<toolchain> Disable the given warnings for the specified toolchain
 #   DISABLED_WARNINGS_<toolchain>_<OS> Disable the given warnings for the specified
 #       toolchain and target OS

make/common/native/Flags.gmk

@@ -194,6 +194,11 @@ define SetupCompilerFlags
     $1_EXTRA_CXXFLAGS += $(CFLAGS_WARNINGS_ARE_ERRORS)
   endif
 
+  ifeq (true, $$($1_LINK_TIME_OPTIMIZATION))
+    $1_EXTRA_CFLAGS += $(C_O_FLAG_LTO)
+    $1_EXTRA_CXXFLAGS += $(CXX_O_FLAG_LTO)
+  endif
+
   ifeq (NONE, $$($1_OPTIMIZATION))
     $1_OPT_CFLAGS := $(C_O_FLAG_NONE)
     $1_OPT_CXXFLAGS := $(CXX_O_FLAG_NONE)
@@ -222,6 +227,10 @@ define SetupLinkerFlags
   # Pickup extra OPENJDK_TARGET_OS_TYPE, OPENJDK_TARGET_OS and TOOLCHAIN_TYPE
   # dependent variables for LDFLAGS and LIBS, and additionally the pair dependent
   # TOOLCHAIN_TYPE plus OPENJDK_TARGET_OS
+  ifeq ($$($1_LINK_TIME_OPTIMIZATION), true)
+    $1_EXTRA_LDFLAGS += $(LDFLAGS_LTO)
+  endif
+
   $1_EXTRA_LDFLAGS += $$($1_LDFLAGS_$(OPENJDK_TARGET_OS_TYPE)) $$($1_LDFLAGS_$(OPENJDK_TARGET_OS)) \
       $$($1_LDFLAGS_$(TOOLCHAIN_TYPE)) $$($1_LDFLAGS_$(TOOLCHAIN_TYPE)_$(OPENJDK_TARGET_OS))
   $1_EXTRA_LIBS += $$($1_LIBS_$(OPENJDK_TARGET_OS_TYPE)) $$($1_LIBS_$(OPENJDK_TARGET_OS)) \

make/hotspot/lib/CompileJvm.gmk

@@ -234,6 +234,7 @@ $(eval $(call SetupJdkLibrary, BUILD_LIBJVM, \
     LDFLAGS := $(JVM_LDFLAGS), \
     LIBS := $(JVM_LIBS), \
     OPTIMIZATION := $(JVM_OPTIMIZATION), \
+    LINK_TIME_OPTIMIZATION := $(JVM_LTO), \
     OBJECT_DIR := $(JVM_OUTPUTDIR)/objs, \
     STRIPFLAGS := $(JVM_STRIPFLAGS), \
     EMBED_MANIFEST := true, \

make/hotspot/lib/JvmFeatures.gmk

@@ -175,22 +175,12 @@ ifeq ($(call check-jvm-feature, link-time-opt), true)
   # Set JVM_OPTIMIZATION directly so other jvm-feature flags can override it
   # later on if desired
   JVM_OPTIMIZATION := HIGHEST_JVM
-  ifeq ($(call isCompiler, gcc), true)
+  JVM_LTO := true
-    JVM_CFLAGS_FEATURES += -flto=auto -fuse-linker-plugin -fno-strict-aliasing \
+  ifneq ($(call isCompiler, microsoft), true)
-        -fno-fat-lto-objects
+    JVM_LDFLAGS_FEATURES += $(CXX_O_FLAG_HIGHEST_JVM)
-    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
   endif
 else
+  JVM_LTO := false
   ifeq ($(call isCompiler, gcc), true)
     JVM_LDFLAGS_FEATURES += -O1
   endif

make/modules/java.desktop/lib/ClientLibraries.gmk

@@ -226,6 +226,7 @@ ifeq ($(ENABLE_HEADLESS_ONLY), false)
       EXCLUDE_FILES := imageioJPEG.c jpegdecoder.c pngtest.c, \
       EXCLUDES := $(LIBSPLASHSCREEN_EXCLUDES), \
       OPTIMIZATION := SIZE, \
+      LINK_TIME_OPTIMIZATION := true, \
       CFLAGS := $(LIBSPLASHSCREEN_CFLAGS) \
           $(GIFLIB_CFLAGS) $(LIBJPEG_CFLAGS) $(PNG_CFLAGS) $(LIBZ_CFLAGS) \
           $(ICONV_CFLAGS), \