[WebAssembly] Strip threadlocal attribute from globals in single thread mode

dschuff · dschuff · commit 39b5367cba5d · 2018-03-20T22:01:32.000Z
The default thread model for wasm is single, and in this mode thread-local global variables can be lowered identically to non-thread-local variables. Differential Revision: https://reviews.llvm.org/D44703 llvm-svn: 328049
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -126,6 +126,22 @@ WebAssemblyTargetMachine::getSubtargetImpl(const Function &F) const {
 }
 
 namespace {
+class StripThreadLocal final : public ModulePass {
+  // The default thread model for wasm is single, where thread-local variables
+  // are identical to regular globals and should be treated the same. So this
+  // pass just converts all GlobalVariables to NotThreadLocal
+  static char ID;
+
+ public:
+  StripThreadLocal() : ModulePass(ID) {}
+  bool runOnModule(Module &M) override {
+    for (auto &GV : M.globals())
+      GV.setThreadLocalMode(GlobalValue::ThreadLocalMode::NotThreadLocal);
+    return true;
+  }
+};
+char StripThreadLocal::ID = 0;
+
 /// WebAssembly Code Generator Pass Configuration Options.
 class WebAssemblyPassConfig final : public TargetPassConfig {
 public:
@@ -166,13 +182,15 @@ FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
 //===----------------------------------------------------------------------===//
 
 void WebAssemblyPassConfig::addIRPasses() {
-  if (TM->Options.ThreadModel == ThreadModel::Single)
+  if (TM->Options.ThreadModel == ThreadModel::Single) {
     // In "single" mode, atomics get lowered to non-atomics.
     addPass(createLowerAtomicPass());
-  else
+    addPass(new StripThreadLocal());
+  } else {
     // Expand some atomic operations. WebAssemblyTargetLowering has hooks which
     // control specifically what gets lowered.
     addPass(createAtomicExpandPass());
+  }
 
   // Lower .llvm.global_dtors into .llvm_global_ctors with __cxa_atexit calls.
   addPass(createWebAssemblyLowerGlobalDtors());
diff --git a/llvm/test/CodeGen/WebAssembly/tls.ll b/llvm/test/CodeGen/WebAssembly/tls.ll
@@ -0,0 +1,17 @@
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -disable-wasm-explicit-locals -thread-model=single | FileCheck --check-prefix=SINGLE %s
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+; SINGLE-LABEL: address_of_tls:
+define i32 @address_of_tls() {
+  ; SINGLE: i32.const $push0=, tls
+  ; SINGLE-NEXT: return $pop0
+  ret i32 ptrtoint(i32* @tls to i32)
+}
+
+; SINGLE: .type	tls,@object
+; SINGLE-NEXT: .section	.bss.tls,"",@
+; SINGLE-NEXT: .p2align 2
+; SINGLE-NEXT: tls:
+; SINGLE-NEXT: .int32 0
+@tls = internal thread_local global i32 0
