[flang] [clang] [flang][Driver] Support -pthread in the frontend (PR #77360)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu updated https://github.com/llvm/llvm-project/pull/77360

>From ab27280e85d6027e6ff119c0803d962753e83b52 Mon Sep 17 00:00:00 2001
From: Tarun Prabhu <tarun at lanl.gov>
Date: Mon, 8 Jan 2024 10:56:09 -0700
Subject: [PATCH] [flang][Driver] Support -pthread in the frontend

The -pthread option is supported by both clang and gfortran.
---
 clang/include/clang/Driver/Options.td    |  3 ++-
 flang/test/Driver/driver-help-hidden.f90 |  1 +
 flang/test/Driver/driver-help.f90        |  2 ++
 flang/test/Driver/pthread.f90            | 22 ++++++++++++++++++++++
 4 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 flang/test/Driver/pthread.f90

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d9d6ce81b4d84af..a4a988c71ec412c 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -5307,7 +5307,8 @@ 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, FC1Option]>>;
 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/driver-help-hidden.f90 b/flang/test/Driver/driver-help-hidden.f90
index a84db70845694e6..426b0e5a1c367d7 100644
--- a/flang/test/Driver/driver-help-hidden.f90
+++ b/flang/test/Driver/driver-help-hidden.f90
@@ -139,6 +139,7 @@
 ! CHECK-NEXT: -pedantic               Warn on language extensions
 ! CHECK-NEXT: -print-effective-triple Print the effective target triple
 ! CHECK-NEXT: -print-target-triple    Print the normalized target triple
+! CHECK-NEXT: -pthread                Support POSIX threads in generated code
 ! CHECK-NEXT: -P                      Disable linemarker output in -E mode
 ! CHECK-NEXT: -Rpass-analysis=<value> Report transformation analysis from optimization passes whose name matches the given POSIX regular expression
 ! CHECK-NEXT: -Rpass-missed=<value>   Report missed transformations by optimization passes whose name matches the given POSIX regular expression
diff --git a/flang/test/Driver/driver-help.f90 b/flang/test/Driver/driver-help.f90
index e5cc8a20237651a..221da6439764b4d 100644
--- a/flang/test/Driver/driver-help.f90
+++ b/flang/test/Driver/driver-help.f90
@@ -125,6 +125,7 @@
 ! HELP-NEXT: -pedantic               Warn on language extensions
 ! HELP-NEXT: -print-effective-triple Print the effective target triple
 ! HELP-NEXT: -print-target-triple    Print the normalized target triple
+! HELP-NEXT: -pthread                Support POSIX threads in generated code
 ! HELP-NEXT: -P                      Disable linemarker output in -E mode
 ! HELP-NEXT: -Rpass-analysis=<value> Report transformation analysis from optimization passes whose name matches the given POSIX regular expression
 ! HELP-NEXT: -Rpass-missed=<value>   Report missed transformations by optimization passes whose name matches the given POSIX regular expression
@@ -265,6 +266,7 @@
 ! HELP-FC1-NEXT: -pic-is-pie             File is for a position independent executable
 ! HELP-FC1-NEXT: -pic-level <value>      Value for __PIC__
 ! HELP-FC1-NEXT: -plugin <name>          Use the named plugin action instead of the default action (use "help" to list available options)
+! HELP-FC1-NEXT: -pthread                Support POSIX threads in generated code
 ! HELP-FC1-NEXT: -P                      Disable linemarker output in -E mode
 ! HELP-FC1-NEXT: -Rpass-analysis=<value> Report transformation analysis from optimization passes whose name matches the given POSIX regular expression
 ! HELP-FC1-NEXT: -Rpass-missed=<value>   Report missed transformations by optimization passes whose name matches the given POSIX regular expression
diff --git a/flang/test/Driver/pthread.f90 b/flang/test/Driver/pthread.f90
new file mode 100644
index 000000000000000..6201f4d9f9c2177
--- /dev/null
+++ b/flang/test/Driver/pthread.f90
@@ -0,0 +1,22 @@
+! In release 2.34, glibc removed libpthread as a separate library. All the
+! pthread_* functions were subsumed into libc, so linking that is sufficient.
+! However, when linking against older glibc builds, the explicit link of
+! -pthread will be required. More details are here:
+!
+! https://developers.redhat.com/articles/2021/12/17/why-glibc-234-removed-libpthread#the_developer_view
+!
+! This makes it difficult to write a test that requires the -pthread flag in
+! order to pass. Checking for the presence of -lpthread in the linker flags is
+! not reliable since the linker could just skip the flag altogether if it is
+! linking against a new libc implementation.
+
+! RUN: %flang -### -pthread /dev/null -o /dev/null 2>&1 | FileCheck %s
+! RUN: %flang -### -Xflang -pthread /dev/null -o /dev/null 2>&1 | FileCheck %s
+
+! How the -pthread flag is handled is very platform-specific. A lot of that
+! functionality is tested by clang, and the flag itself is handled by clang's
+! driver that flang also uses. Instead of duplicating all that testing here,
+! just check that the presence of the flag does not raise an error. If we need
+! more customized handling of -pthread, the tests for that can be added here.
+!
+! CHECK-NOT: error: