[clang] [Clang][Driver] Declare win32 threads on Windows (PR #121442)

[Mateusz Mikuła via cfe-commits]

https://github.com/mati865 created https://github.com/llvm/llvm-project/pull/121442

Fixes https://github.com/llvm/llvm-project/issues/10148

Recently I saw a user confused by it and thought Clang was using `winpthreads`.

Note: this does not change structures like https://github.com/llvm/llvm-project/blob/0cbe28df7100bf4384f84542d602f90cb783a2d4/clang/include/clang/Basic/LangOptions.h#L360 which still yield `posix`.

>From cc7708f2646326c5065c4853a8a2971db48e3718 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Miku=C5=82a?= <mati865 at gmail.com>
Date: Wed, 1 Jan 2025 21:38:49 +0100
Subject: [PATCH] [Clang][Driver] Declare win32 threads on Windows

Fixes https://github.com/llvm/llvm-project/issues/10148
---
 clang/include/clang/Driver/ToolChain.h |  8 +++++++-
 clang/lib/Driver/ToolChains/Clang.cpp  |  2 +-
 clang/test/Driver/thread-model.c       | 10 +++++++---
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/clang/include/clang/Driver/ToolChain.h b/clang/include/clang/Driver/ToolChain.h
index 5347e29be91439..9db12486d4d833 100644
--- a/clang/include/clang/Driver/ToolChain.h
+++ b/clang/include/clang/Driver/ToolChain.h
@@ -619,7 +619,13 @@ class ToolChain {
   virtual bool SupportsEmbeddedBitcode() const { return false; }
 
   /// getThreadModel() - Which thread model does this target use?
-  virtual std::string getThreadModel() const { return "posix"; }
+  virtual std::string getThreadModel() const {
+#ifdef _WIN32
+    return "win32";
+#else
+    return "posix";
+#endif
+  }
 
   /// isThreadModelSupported() - Does this target support a thread model?
   virtual bool isThreadModelSupported(const StringRef Model) const;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index a020e00cd17392..bc181dfddc6398 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5792,7 +5792,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       Model = A->getValue();
     } else
       Model = TC.getThreadModel();
-    if (Model != "posix") {
+    if (Model != "posix" && Model != "win32") {
       CmdArgs.push_back("-mthread-model");
       CmdArgs.push_back(Args.MakeArgString(Model));
     }
diff --git a/clang/test/Driver/thread-model.c b/clang/test/Driver/thread-model.c
index 9abe5f11d9aab9..a07f8913630a35 100644
--- a/clang/test/Driver/thread-model.c
+++ b/clang/test/Driver/thread-model.c
@@ -1,5 +1,6 @@
 // RUN: %clang -### -target arm-unknown-linux-gnu -c %s -mthread-model posix -v 2>&1 | FileCheck %s
-// RUN: %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck %s
+// RUN: %if !system-windows %{ %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck %s %}
+// RUN: %if system-windows %{ %clang -### -target arm-unknown-linux-gnu -c %s -v 2>&1 | FileCheck --check-prefix=WIN32 %s %}
 // RUN: %clang -### -target arm-unknown-linux-gnu -c %s -mthread-model single -v 2>&1 | FileCheck --check-prefix=SINGLE %s
 // RUN: not %clang -target arm-unknown-linux-gnu -c %s -mthread-model silly -v 2>&1 | FileCheck --check-prefix=INVALID %s
 
@@ -8,9 +9,12 @@
 // SINGLE: Thread model: single
 // SINGLE: "-mthread-model" "single"
 // INVALID: error: invalid thread model 'silly' in '-mthread-model silly' for this target
+// WIN32: Thread model: win32
 
-// RUN: %clang -### -target wasm32-unknown-linux-gnu -c %s -v 2>&1 | FileCheck %s
+// RUN: %if !system-windows %{ %clang -### -target wasm32-unknown-linux-gnu -c %s -v 2>&1 | FileCheck %s %}
+// RUN: %if system-windows %{ %clang -### -target wasm32-unknown-linux-gnu -c %s -v 2>&1 | FileCheck --check-prefix=WIN32 %s %}
 // RUN: %clang -### -target wasm32-unknown-linux-gnu -c %s -v -mthread-model single 2>&1 | FileCheck --check-prefix=SINGLE %s
 // RUN: %clang -### -target wasm32-unknown-linux-gnu -c %s -v -mthread-model posix 2>&1 | FileCheck %s
 // RUN: not %clang -### --target=wasm32-unknown-linux-gnu -c %s -v -mthread-model silly 2>&1 | FileCheck --check-prefix=INVALID %s
-// RUN: %clang -### -target wasm64-unknown-linux-gnu -c %s -v 2>&1 | FileCheck %s
+// RUN: %if !system-windows %{ %clang -### -target wasm64-unknown-linux-gnu -c %s -v 2>&1 | FileCheck %s %}
+// RUN: %if system-windows %{ %clang -### -target wasm64-unknown-linux-gnu -c %s -v 2>&1 | FileCheck --check-prefix=WIN32 %s %}