[Clang] add option --offload-jobs=N

for specifying number of threads for clang-linker-wrapper. By
default it uses half of hardware threads.

Author: yxsamliu

clang/include/clang/Driver/Options.td

@@ -1233,6 +1233,10 @@ def offload_compression_level_EQ : Joined<["--"], "offload-compression-level=">,
   Flags<[HelpHidden]>,
   HelpText<"Compression level for offload device binaries (HIP only)">;
 
+def offload_jobs_EQ : Joined<["--"], "offload-jobs=">,
+  HelpText<"Set the number of threads for the clang-linker-wrapper. Defaults to"
+           " half of the available hardware threads if not specified.">;
+
 defm offload_via_llvm : BoolFOption<"offload-via-llvm",
   LangOpts<"OffloadViaLLVM">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option], "Use">,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -57,6 +57,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
+#include "llvm/Support/ThreadPool.h"
 #include "llvm/Support/YAMLParser.h"
 #include "llvm/TargetParser/AArch64TargetParser.h"
 #include "llvm/TargetParser/ARMTargetParserCommon.h"
@@ -1031,6 +1032,7 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
     if (JA.isOffloading(Action::OFK_HIP)) {
       Args.ClaimAllArgs(options::OPT_offload_compress);
       Args.ClaimAllArgs(options::OPT_no_offload_compress);
+      Args.ClaimAllArgs(options::OPT_offload_jobs_EQ);
     }
 
     bool HasTarget = false;
@@ -9360,6 +9362,19 @@ void LinkerWrapper::ConstructJob(Compilation &C, const JobAction &JA,
       CmdArgs.push_back(LinkArg);
 
   addOffloadCompressArgs(Args, CmdArgs);
+
+  // Default to half of hardware threads if users do not specify it.
+  if (Arg *A = Args.getLastArg(options::OPT_offload_jobs_EQ))
+    CmdArgs.push_back(
+        Args.MakeArgString(Twine("--wrapper-jobs=") + A->getValue()));
+  else {
+    unsigned NumThreads =
+        llvm::hardware_concurrency().compute_thread_count() / 2;
+    if (NumThreads > 1)
+      CmdArgs.push_back(
+          Args.MakeArgString(Twine("--wrapper-jobs=") + Twine(NumThreads)));
+  }
+
   const char *Exec =
       Args.MakeArgString(getToolChain().GetProgramPath("clang-linker-wrapper"));
 

clang/test/Driver/hip-options.hip

@@ -243,6 +243,13 @@
 // NO-WARN-ATOMIC-NOT: clang{{.*}} "-triple" "x86_64-unknown-linux-gnu" {{.*}} "-Werror=atomic-alignment"
 // NO-WARN-ATOMIC-NOT: clang{{.*}} "-triple" "x86_64-unknown-linux-gnu" {{.*}} "-Wno-error=atomic-alignment"
 
-// Check --offload-compress does not cause warning.
+// Check --offload-compress --offload-jobs=N does not cause warning.
 // RUN: %clang -### -Werror --target=x86_64-unknown-linux-gnu -nogpuinc -nogpulib \
-// RUN:   --offload-arch=gfx1100 --offload-compress --offload-host-only -M %s
+// RUN:   --offload-arch=gfx1100 --offload-compress --offload-host-only -M %s \
+// RUN:   --offload-jobs=4
+
+// Check --offload-jobs=N passed to linker wrapper.
+// RUN: %clang -### -Werror --target=x86_64-unknown-linux-gnu -nogpuinc -nogpulib \
+// RUN:   --offload-arch=gfx1100 --offload-new-driver --offload-jobs=4 %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=JOBS %s
+// JOBS: clang-linker-wrapper{{.*}} "--wrapper-jobs=4"