Add PGO support for Clang/LLVM on Unix (dotnet#10533)

Extend PGO support from VC++ on WIN32 to Clang/LLVM on UNIX as well.
* Just like on Windows: if profile data is missing, skip enabling PGO
  (allows non-PGO builds in branches where we don't publish PGO data).
* PGO with LTO requires additional dependencies (namely a discoverable
  `ld.gold` and `LLVMgold.so`). To protect against broken support and
  keep the build flexible across a wider array of distros, attempt to
  detect whether PGO compilation would work (using cmake's
  `try_compile()`), and fall back to a non-PGO/non-LTO build if the test
  fails.

CMakeLists.txt

@@ -11,6 +11,9 @@ project(CoreCLR)
 # Include cmake functions
 include(functions.cmake)
 
+# Include global configure settings
+include(configure.cmake)
+
 if (WIN32)
   message(STATUS "VS_PLATFORM_TOOLSET is ${CMAKE_VS_PLATFORM_TOOLSET}")
   message(STATUS "VS_PLATFORM_NAME is ${CMAKE_VS_PLATFORM_NAME}")

configure.cmake

@@ -0,0 +1,12 @@
+include(CheckCXXSourceCompiles)
+
+# VC++ guarantees support for LTCG (LTO's equivalent)
+if(NOT WIN32)
+  # Function required to give CMAKE_REQUIRED_* local scope
+  function(check_have_lto)
+    set(CMAKE_REQUIRED_FLAGS -flto)
+    set(CMAKE_REQUIRED_LIBRARIES -flto -fuse-ld=gold)
+    check_cxx_source_compiles("int main() { return 0; }" HAVE_LTO)
+  endfunction(check_have_lto)
+  check_have_lto()
+endif(NOT WIN32)

pgosupport.cmake

@@ -10,6 +10,9 @@ endfunction(clr_pgo_unknown_arch)
 function(add_pgo TargetName)
     if(WIN32)
         set(ProfileFileName "${TargetName}.pgd")
+    else(WIN32)
+        # Clang/LLVM uses one profdata file for the entire repo
+        set(ProfileFileName "coreclr.profdata")
     endif(WIN32)
 
     set(CLR_CMAKE_OPTDATA_PACKAGEWITHRID "optimization.${CLR_CMAKE_TARGET_OS}-${CLR_CMAKE_TARGET_ARCH}.PGO.CoreCLR")
@@ -18,24 +21,32 @@ function(add_pgo TargetName)
         ProfilePath
     )
 
-    # Enable PGO only for optimized configs
-    set(ConfigTypeList RELEASE RELWITHDEBINFO)
-
-    foreach(ConfigType IN LISTS ConfigTypeList)
-        set(LinkFlagsProperty "LINK_FLAGS_${ConfigType}")
-        if(CLR_CMAKE_PGO_INSTRUMENT)
+    if(CLR_CMAKE_PGO_INSTRUMENT)
+        if(WIN32)
+            set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS_RELEASE        " /LTCG /GENPROFILE")
+            set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS_RELWITHDEBINFO " /LTCG /GENPROFILE")
+        else(WIN32)
+            if(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELEASE OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELWITHDEBINFO)
+                target_compile_options(${TargetName} PRIVATE -flto -fprofile-instr-generate)
+                set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS " -flto -fuse-ld=gold -fprofile-instr-generate")
+            endif(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELEASE OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELWITHDEBINFO)
+        endif(WIN32)
+    else(CLR_CMAKE_PGO_INSTRUMENT)
+        # If we don't have profile data availble, gracefully fall back to a non-PGO opt build
+        if(EXISTS ${ProfilePath})
             if(WIN32)
-                set_property(TARGET ${TargetName} APPEND_STRING PROPERTY ${LinkFlagsProperty} "/LTCG /GENPROFILE")
+                set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS_RELEASE        " /LTCG /USEPROFILE:PGD=${ProfilePath}")
+                set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS_RELWITHDEBINFO " /LTCG /USEPROFILE:PGD=${ProfilePath}")
+            else(WIN32)
+                if(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELEASE OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELWITHDEBINFO)
+                    if(HAVE_LTO)
+                        target_compile_options(${TargetName} PRIVATE -flto -fprofile-instr-use=${ProfilePath})
+                        set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS " -flto -fuse-ld=gold -fprofile-instr-use=${ProfilePath}")
+                    endif(HAVE_LTO)
+                endif(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELEASE OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELWITHDEBINFO)
             endif(WIN32)
-        else(CLR_CMAKE_PGO_INSTRUMENT)
-            # If we don't have profile data availble, gracefully fall back to a non-PGO opt build
-            if(EXISTS ${ProfilePath})
-                if(WIN32)
-                    set_property(TARGET ${TargetName} APPEND_STRING PROPERTY ${LinkFlagsProperty} "/LTCG /USEPROFILE:PGD=${ProfilePath}")
-                endif(WIN32)
-            endif(EXISTS ${ProfilePath})
-        endif(CLR_CMAKE_PGO_INSTRUMENT)
-    endforeach(ConfigType)
+        endif(EXISTS ${ProfilePath})
+    endif(CLR_CMAKE_PGO_INSTRUMENT)
 endfunction(add_pgo)
 
 if(WIN32)