Add support for PGO builds with clang

Summary:
This is also fixes support for PGO under GCC.
There will be files that end up without coverage due to certain tests being disabled because they are too flaky, or else make dangerous changes to the system (like setting the system time), so make the warning this generates not be a hard error.

Also notable is that under clang, the default target when running `make all` remains as `build_all` rather than `profile-opt` in order to support some internal build scenarios. With clang, explicitly building with `make profile-opt` will still produce a PGO'd binary.

Reviewed By: carljm

Differential Revision: D36238598

fbshipit-source-id: 3e1fbf5

configure

@@ -6633,6 +6633,7 @@ $as_echo "$as_me: llvm-ar found via xcrun: ${LLVM_AR}" >&6;}
   fi
 
   CFLAGS_NODIST="$CFLAGS_NODIST $LTOFLAGS"
+  CXXFLAGS_NODIST="$CXXFLAGS_NODIST $LTOFLAGS"
   LDFLAGS_NODIST="$LDFLAGS_NODIST $LTOFLAGS"
 fi
 
@@ -6763,11 +6764,26 @@ $as_echo "$as_me: llvm-profdata found via xcrun: ${LLVM_PROFDATA}" >&6;}
 fi
 LLVM_PROF_ERR=no
 case $CC in
+  *clang*)
+    # Any changes made here should be reflected in the GCC+Darwin case below
+    PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
+    PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd -Wno-error=profile-instr-unprofiled"
+    LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
+    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+    if test $LLVM_PROF_FOUND = not-found
+    then
+      LLVM_PROF_ERR=yes
+      if test "${REQUIRE_PGO}" = "yes"
+      then
+        as_fn_error $? "llvm-profdata is required for a --enable-optimizations build but could not be found." "$LINENO" 5
+      fi
+    fi
+    ;;
   *gcc*)
     case $ac_sys_system in
       Darwin*)
         PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
-        PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
+        PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd -Wno-error=profile-instr-unprofiled"
         LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
         LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
         if test "${LLVM_PROF_FOUND}" = "not-found"
@@ -6781,7 +6797,7 @@ case $CC in
         ;;
       *)
         PGO_PROF_GEN_FLAG="-fprofile-generate"
-        PGO_PROF_USE_FLAG="-fprofile-use -fprofile-correction"
+        PGO_PROF_USE_FLAG="-fprofile-use -fprofile-correction -Wno-error=missing-profile"
         LLVM_PROF_MERGER="true"
         LLVM_PROF_FILE=""
         ;;

configure.ac

@@ -1381,6 +1381,7 @@ if test "$Py_LTO" = 'true' ; then
   fi
 
   CFLAGS_NODIST="$CFLAGS_NODIST $LTOFLAGS"
+  CXXFLAGS_NODIST="$CXXFLAGS_NODIST $LTOFLAGS"
   LDFLAGS_NODIST="$LDFLAGS_NODIST $LTOFLAGS"
 fi
 
@@ -1413,11 +1414,26 @@ then
 fi
 LLVM_PROF_ERR=no
 case $CC in
+  *clang*)
+    # Any changes made here should be reflected in the GCC+Darwin case below
+    PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
+    PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd -Wno-error=profile-instr-unprofiled"
+    LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
+    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+    if test "$LLVM_PROF_FOUND" = "not-found"
+    then
+      LLVM_PROF_ERR=yes
+      if test "${REQUIRE_PGO}" = "yes"
+      then
+        AC_MSG_ERROR([llvm-profdata is required for a --enable-optimizations build but could not be found.])
+      fi
+    fi
+    ;;
   *gcc*)
     case $ac_sys_system in
       Darwin*)
         PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
-        PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
+        PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd -Wno-error=profile-instr-unprofiled"
         LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
         LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
         if test "${LLVM_PROF_FOUND}" = "not-found"
@@ -1431,7 +1447,7 @@ case $CC in
         ;;
       *)
         PGO_PROF_GEN_FLAG="-fprofile-generate"
-        PGO_PROF_USE_FLAG="-fprofile-use -fprofile-correction"
+        PGO_PROF_USE_FLAG="-fprofile-use -fprofile-correction -Wno-error=missing-profile"
         LLVM_PROF_MERGER="true"
         LLVM_PROF_FILE=""
         ;;