[lld-macho] Initialize separate time trace profiler for mapfile worker

[int3]

Summary

After D115416: [lld-macho] Make writing map file asynchronous, the "Write map file" event no longer shows up
in the time trace. Each time trace profiler instance is thread-local,
but we had neglected to initialize a separate instance for the mapfile
worker thread.

[int3]

Note: The LTO backend initializes the time trace profiler in a similar fashion: https://github.com/llvm/llvm-project/blob/f0b2a1a629dab17f2ea161a9281d8dc63b37a7a0/llvm/lib/LTO/LTO.cpp#L1271

[dexonsmith]

Looks like this commit makes the test flakey somehow.

• lld-x86_64-ubuntu-fast failed it tested this commit: https://lab.llvm.org/buildbot/#/builders/58/builds/16007
• Passed in the next commit, then failed again here: https://lab.llvm.org/buildbot/#/builders/58/builds/16009
• Then recovered again...

[thakis]

This seems to break tests: http://45.33.8.238/macm1/25367/step_10.txt

Please take a look, and revert for now if takes a while to fix.

[thakis]

Seems to not fail every time though.

[int3]

Hm it seems that "Total Write map file" always exists, but the "Write map file" sub-event may or may not be emitted. Maybe it depends on whether that even occurs concurrently with other events?

I'll change the test to check for "Total Write map file" and see if that fixes things.

lld/MachO/Writer.cpp

template <class LP> void Writer::run() {
   // After this point, we create no new segments; HOWEVER, we might
   // yet create branch-range extension thunks for architectures whose
   // hardware call instructions have limited range, e.g., ARM(64).
   // The thunks are created as InputSections interspersed among
   // the ordinary __TEXT,_text InputSections.
   sortSegmentsAndSections();
   createLoadCommands<LP>();
   finalizeAddresses();
-  threadPool.async(writeMapFile);
+  threadPool.async([&] {
+    if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
+      timeTraceProfilerInitialize(config->timeTraceGranularity, "writeMapFile");
+    writeMapFile();
+    if (LLVM_ENABLE_THREADS && config->timeTraceEnabled)
+      timeTraceProfilerFinishThread();
+  });
   finalizeLinkEditSegment();
   writeOutputFile();
 }
 
 template <class LP> void macho::writeResult() { Writer().run<LP>(); }
 
 void macho::resetWriter() { LCDylib::resetInstanceCount(); }
 

lld/test/MachO/map-file.s

 # REQUIRES: x86
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/foo.s -o %t/foo.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
 
-# RUN: %lld -map %t/map %t/test.o %t/foo.o -o %t/test-map
+# RUN: %lld -map %t/map %t/test.o %t/foo.o --time-trace -o %t/test-map
 # RUN: llvm-objdump --syms --section-headers %t/test-map > %t/objdump
 # RUN: cat %t/objdump %t/map > %t/out
 # RUN: FileCheck %s < %t/out
+# RUN: FileCheck %s --check-prefix=MAPFILE < %t/test-map.time-trace
 
 #--- foo.s
 .section __TEXT,obj
 .globl _foo
 _foo:
 
 #--- test.s
 .comm _number, 1

 # CHECK-NEXT: 0x[[#DATA]]  0x{{[0-9a-f]+}}   __TEXT  obj
 # CHECK-NEXT: 0x[[#BSS]]   0x{{[0-9a-f]+}}   __DATA  __common
 
 # CHECK-NEXT: # Symbols:
 # CHECK-NEXT: # Address        File  Name
 # CHECK-NEXT: 0x[[#NUMBER]]    [  1]  _number
 # CHECK-NEXT: 0x[[#MAIN]]      [  1]  _main
 # CHECK-NEXT: 0x[[#FOO]]       [  2]  _foo
+
+# MAPFILE: "name":"Write map file"