[clang] [clang][WebAssembly] Always have `-pthread` imply `--shared-memory` linker flag (PR #127939)

[Sam Clegg via cfe-commits]

https://github.com/sbc100 updated https://github.com/llvm/llvm-project/pull/127939

>From e788e756cac0c7b6f78479adbaea1a86f8005fb6 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc at chromium.org>
Date: Wed, 19 Feb 2025 17:26:41 -0800
Subject: [PATCH] [clang][WebAssembly] Always have `-pthread` imply
 `--shared-memory` linker flag

Unlike `-lpthread` this flag should not be suppressed by `-nostdlib`.
---
 clang/lib/Driver/ToolChains/WebAssembly.cpp |  7 ++++---
 clang/test/Driver/wasm-toolchain.c          | 11 ++++++++---
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
index bd25fd1a8933a..93f17a03c580f 100644
--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
+++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
@@ -150,14 +150,15 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 
+  if (Args.hasArg(options::OPT_pthread))
+    CmdArgs.push_back("--shared-memory");
+
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
     if (ToolChain.ShouldLinkCXXStdlib(Args))
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
 
-    if (Args.hasArg(options::OPT_pthread)) {
+    if (Args.hasArg(options::OPT_pthread))
       CmdArgs.push_back("-lpthread");
-      CmdArgs.push_back("--shared-memory");
-    }
 
     CmdArgs.push_back("-lc");
     AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
diff --git a/clang/test/Driver/wasm-toolchain.c b/clang/test/Driver/wasm-toolchain.c
index f516a4e457da7..1ad219338ac28 100644
--- a/clang/test/Driver/wasm-toolchain.c
+++ b/clang/test/Driver/wasm-toolchain.c
@@ -75,11 +75,16 @@
 // Thread-related command line tests.
 
 // '-pthread' sets +atomics, +bulk-memory, +mutable-globals, +sign-ext, and --shared-memory
-// RUN: %clang -### --target=wasm32-unknown-unknown \
-// RUN:    --sysroot=/foo %s -pthread 2>&1 \
+// RUN: %clang -### --target=wasm32-unknown-unknown --sysroot=/foo %s -pthread 2>&1 \
 // RUN:  | FileCheck -check-prefix=PTHREAD %s
 // PTHREAD: "-cc1" {{.*}} "-target-feature" "+atomics" "-target-feature" "+bulk-memory" "-target-feature" "+mutable-globals" "-target-feature" "+sign-ext"
-// PTHREAD: wasm-ld{{.*}}" "-lpthread" "--shared-memory"
+// PTHREAD: wasm-ld{{.*}}" "--shared-memory" "-lpthread"
+//
+// '-pthread' with '-nostdlib' should still set '--shared-memory' but not include '-lpthread'
+// RUN: %clang -### --target=wasm32-unknown-unknown --sysroot=/foo %s -pthread -nostdlib 2>&1 \
+// RUN:  | FileCheck -check-prefix=PTHREAD-NOSTDLIB %s
+// PTHREAD-NOSTDLIB: "-cc1" {{.*}} "-target-feature" "+atomics" "-target-feature" "+bulk-memory" "-target-feature" "+mutable-globals" "-target-feature" "+sign-ext"
+// PTHREAD-NOSTDLIB: wasm-ld{{.*}}" "--shared-memory" "-o" "a.out"
 
 // '-pthread' not allowed with '-mno-atomics'
 // RUN: not %clang -### --target=wasm32-unknown-unknown \