Strip dead code when linking by default with BFD ld (linux, ...) and ld64 (os x).

This reduces the size of clang-format from 22 MB to 1.8 MB, diagtool goes from
21 MB to 2.8 MB, libclang.so goes from 29 MB to 20 MB, etc.  The size of the
bin/ folder shrinks from 270 MB to 200 MB.

Targets that support plugins and don't already use EXPORTED_SYMBOL_FILE
(which libclang and libLTO already do) can set NO_DEAD_STRIP to opt out.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198087 91177308-0d34-0410-b5e6-96231b3b80d8

Makefile.rules

@@ -608,6 +608,22 @@ ifndef KEEP_SYMBOLS
   Install.StripFlag += -s
 endif
 
+# By default, strip dead symbols at link time
+ifneq ($(HOST_OS), $(filter $(HOST_OS), Cygwin MingW))
+ifneq ($(HOST_OS),Darwin)
+  CXX.Flags += -ffunction-sections -fdata-sections
+endif
+endif
+ifndef NO_DEAD_STRIP
+  ifeq ($(HOST_OS),Darwin)
+    LD.Flags += -Wl,-dead_strip
+  else
+    ifneq ($(HOST_OS), $(filter $(HOST_OS), Cygwin MingW))
+      LD.Flags += -Wl,--gc-sections
+    endif
+  endif
+endif
+
 # Adjust linker flags for building an executable
 ifneq ($(HOST_OS), $(filter $(HOST_OS), Cygwin MingW))
   ifndef TOOL_NO_EXPORTS

tools/bugpoint/Makefile

@@ -12,4 +12,7 @@ TOOLNAME := bugpoint
 LINK_COMPONENTS := asmparser instrumentation scalaropts ipo linker bitreader \
                    bitwriter irreader vectorize objcarcopts
 
+# Support plugins.
+NO_DEAD_STRIP := 1
+
 include $(LEVEL)/Makefile.common

tools/llc/Makefile

@@ -11,5 +11,8 @@ LEVEL := ../..
 TOOLNAME := llc
 LINK_COMPONENTS := all-targets bitreader asmparser irreader
 
+# Support plugins.
+NO_DEAD_STRIP := 1
+
 include $(LEVEL)/Makefile.common
 

tools/llvm-shlib/Makefile

@@ -49,9 +49,6 @@ ifeq ($(HOST_OS),Darwin)
     endif
     # Include everything from the .a's into the shared library.
     LLVMLibsOptions    := $(LLVMLibsOptions) -all_load
-    # extra options to override libtool defaults 
-    LLVMLibsOptions    := $(LLVMLibsOptions)  \
-                         -Wl,-dead_strip
 
     # Mac OS X 10.4 and earlier tools do not allow a second -install_name on command line
     DARWIN_VERS := $(shell echo $(TARGET_TRIPLE) | sed 's/.*darwin\([0-9]*\).*/\1/')

tools/lto/Makefile

@@ -37,9 +37,6 @@ ifeq ($(HOST_OS),Darwin)
                         -Wl,$(LTO_LIBRARY_VERSION).$(LLVM_SUBMIT_SUBVERSION) \
                         -Wl,-compatibility_version -Wl,1
     endif
-    # extra options to override libtool defaults 
-    LLVMLibsOptions    := $(LLVMLibsOptions)  \
-                         -Wl,-dead_strip
 
     # Mac OS X 10.4 and earlier tools do not allow a second -install_name on command line
     DARWIN_VERS := $(shell echo $(TARGET_TRIPLE) | sed 's/.*darwin\([0-9]*\).*/\1/')

tools/opt/Makefile

@@ -11,4 +11,7 @@ LEVEL := ../..
 TOOLNAME := opt
 LINK_COMPONENTS := bitreader bitwriter asmparser irreader instrumentation scalaropts objcarcopts ipo vectorize all-targets
 
+# Support plugins.
+NO_DEAD_STRIP := 1
+
 include $(LEVEL)/Makefile.common