[flang][Driver] Support -pthread to the frontend.

[ergawy]

Adds -pthread option to flang. Since the GNU toolchain already adds the required linker flag, we only need to declare FlangOption as one of the supported options for -pthread.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-flang-driver

Author: Kareem Ergawy (ergawy)

Changes

Adds -pthread option to flang. Since the GNU toolchain already adds the required linker flag, we only need to declare FlangOption as one of the supported options for -pthread.

---

Full diff: https://github.com/llvm/llvm-project/pull/75739.diff

2 Files Affected:

• (modified) clang/include/clang/Driver/Options.td (+1-1)
• (modified) flang/test/Driver/dynamic-linker.f90 (+2-1)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 1b02087425b751..b8b8d476413982 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -5297,7 +5297,7 @@ def pthreads : Flag<["-"], "pthreads">;
 defm pthread : BoolOption<"", "pthread",
   LangOpts<"POSIXThreads">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption], "Support POSIX threads in generated code">,
-  NegFlag<SetFalse>, BothFlags<[], [ClangOption, CC1Option]>>;
+  NegFlag<SetFalse>, BothFlags<[], [ClangOption, CC1Option, FlangOption]>>;
 def pie : Flag<["-"], "pie">, Group<Link_Group>;
 def static_pie : Flag<["-"], "static-pie">, Group<Link_Group>;
 def read__only__relocs : Separate<["-"], "read_only_relocs">;
diff --git a/flang/test/Driver/dynamic-linker.f90 b/flang/test/Driver/dynamic-linker.f90
index df119c22a2ea51..57a2af01aadff7 100644
--- a/flang/test/Driver/dynamic-linker.f90
+++ b/flang/test/Driver/dynamic-linker.f90
@@ -1,7 +1,7 @@
 ! Verify that certain linker flags are known to the frontend and are passed on
 ! to the linker.
 
-! RUN: %flang -### --target=x86_64-linux-gnu -rpath /path/to/dir -shared \
+! RUN: %flang -### --target=x86_64-linux-gnu -rpath /path/to/dir -shared -pthread \
 ! RUN:     -static %s 2>&1 | FileCheck \
 ! RUN:     --check-prefixes=GNU-LINKER-OPTIONS %s
 ! RUN: %flang -### --target=x86_64-windows-msvc -rpath /path/to/dir -shared \
@@ -13,6 +13,7 @@
 ! GNU-LINKER-OPTIONS-SAME: "-shared"
 ! GNU-LINKER-OPTIONS-SAME: "-static"
 ! GNU-LINKER-OPTIONS-SAME: "-rpath" "/path/to/dir"
+! GNU-LINKER-OPTIONS-SAME: "-lpthread"
 
 ! For MSVC, adding -static does not add any additional linker options.
 ! MSVC-LINKER-OPTIONS: "{{.*}}link{{(.exe)?}}"

[banach-space]

Hi @ergawy , thanks for this contribution! Could you add a test that would demonstrate compilation failing without -pthread?

[ergawy]

Hi @ergawy , thanks for this contribution! Could you add a test that would demonstrate compilation failing without -pthread?

Thanks for the suggestion. Actually I failed to do that 😆. After looking into it, seems that for the GNU toolchain, the -pthread flag would be redundant. That reason is that the pthread API is defined by libc which is linked in by the driver by default.

I think I will abandon this PR then. Just need to double check once more.

[ergawy]

Abandoning this PR since for the GNU toolchain there is no need to explicitly link with pthread to use the API.