[ThinLTO][gold] Fix filenaming scheme for tasks.

[hoy]

Summary

The gold LTO plugin uses a set of hooks to implements emit-llvm and capture intermediate file generated during LTO. The hooks are called by each lto backend thread with a taskID as argument to differentiate between threads and tasks. Currently, all threads are overwriting the same file which results into only the intermediate output of the last backend thread to be preserved. This diff encodes the taskID into the filename.

[wenlei]

thanks for fix, this looks good to me, but would be good to wait a bit in case others have comments.

[tejohnson]

lgtm with a minor request below.

llvm/tools/gold/gold-plugin.cpp

919

Document constant bool parameter. I.e. "/* TempOutFile */ false"

[hoy]

Addressing tejohnson's comment.

llvm/test/tools/gold/X86/Inputs/emit-llvm.bar.ll

+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local i32 @_Z3barv() #0 {
+  ret i32 0
+}
+
+^0 = module: (path: "bar.o", hash: (3853957065, 2310817429, 3119833948, 1366622700, 2470927843))
+^1 = gv: (name: "_Z3barv", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 1, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 0, returnDoesNotAlias: 0, noInline: 1, alwaysInline: 0)))) ; guid = 17377440600225628772

llvm/test/tools/gold/X86/Inputs/emit-llvm.foo.ll

+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local i32 @_Z3foov() #0 {
+  ret i32 0
+}
+
+^0 = module: (path: "foo.o", hash: (3786635673, 3275786284, 1544384821, 2103351884, 2354656665))
+^1 = gv: (name: "_Z3foov", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 1, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 0, returnDoesNotAlias: 0, noInline: 1, alwaysInline: 0)))) ; guid = 9191153033785521275

llvm/test/tools/gold/X86/thinlto-emit-llvm.ll

+; RUN: llvm-as %p/Inputs/emit-llvm.foo.ll -o %t.foo.bc
+; RUN: llvm-as %p/Inputs/emit-llvm.bar.ll -o %t.bar.bc
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext --shared -plugin-opt thinlto -plugin-opt emit-llvm -m elf_x86_64 %t.foo.bc %t.bar.bc -o %t.bc
+; RUN: llvm-dis %t.bc1 -o - | FileCheck --check-prefix=CHECK-BC1 %s
+; RUN: llvm-dis %t.bc2 -o - | FileCheck --check-prefix=CHECK-BC2 %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK-BC1: define dso_local i32 @_Z3foov()
+define dso_local i32 @_Z3foov() {
+    ret i32 0
+}
+; CHECK-BC2: define dso_local i32 @_Z3barv()
+define dso_local i32 @_Z3barv() {
+    ret i32 0
+}

llvm/tools/gold/gold-plugin.cpp

static std::unique_ptr<LTO> createLTO(IndexWriteCallback OnIndexWrite,
 
   case options::OT_DISABLE:
     Conf.PreOptModuleHook = [](size_t Task, const Module &M) { return false; };
     break;
 
   case options::OT_BC_ONLY:
     Conf.PostInternalizeModuleHook = [](size_t Task, const Module &M) {
       std::error_code EC;
-      raw_fd_ostream OS(output_name, EC, sys::fs::OpenFlags::OF_None);
+      SmallString<128> TaskFilename;
+      getOutputFileName(output_name, /* TempOutFile */ false, TaskFilename,
+                        Task);
+      raw_fd_ostream OS(TaskFilename, EC, sys::fs::OpenFlags::OF_None);
       if (EC)
         message(LDPL_FATAL, "Failed to write the output file.");
       WriteBitcodeToFile(M, OS, /* ShouldPreserveUseListOrder */ false);
       return false;
     };
     break;
 
   case options::OT_SAVE_TEMPS: