[WebAssembly] Set threadmodel during LTO

Subscribers: dschuff, mehdi_amini, inglorion, jgravelle-google, aheejin, sunfish, steven_wu, llvm-commits

Differential Revision: https://reviews.llvm.org/D48689

llvm-svn: 336118

2 files changed, 18 insertions, 1 deletions

diff --git a/lld/test/wasm/lto/atomics.ll b/lld/test/wasm/lto/atomics.ll
new file mode 100644
index 00000000000..a5a82ae2a5f
--- /dev/null
+++ b/lld/test/wasm/lto/atomics.ll
@@ -0,0 +1,14 @@
+; RUN: llvm-as %s -o %t.o
+; RUN: wasm-ld %t.o -o %t.wasm -lto-O0
+; Atomic operations with fail to compile if the ThreadModel is not
+; correctly set to Single (i.e. if atomics are not lowered to regular ops).
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+@foo = hidden global i32 1
+
+define void @_start() {
+  %1 = load atomic i32, i32* @foo unordered, align 4
+  ret void
+}
diff --git a/lld/wasm/LTO.cpp b/lld/wasm/LTO.cpp
index dd66c67e39f..f15551da8b8 100644
--- a/lld/wasm/LTO.cpp
+++ b/lld/wasm/LTO.cpp
@@ -45,10 +45,13 @@ static std::unique_ptr<lto::LTO> createLTO() {
   lto::Config C;
   C.Options = InitTargetOptionsFromCodeGenFlags();
 
-  // Always emit a section per function/datum with LTO.
+  // Always emit a section per function/data with LTO.
   C.Options.FunctionSections = true;
   C.Options.DataSections = true;
 
+  // Wasm currently only supports ThreadModel::Single
+  C.Options.ThreadModel = ThreadModel::Single;
+
   C.DisableVerify = Config->DisableVerify;
   C.DiagHandler = diagnosticHandler;
   C.OptLevel = Config->LTOO;