[DXIL] Don't generate per-variable guards for DirectX

clang/lib/Basic/Targets/DirectX.h

@@ -94,6 +94,13 @@ class LLVM_LIBRARY_VISIBILITY DirectXTargetInfo : public TargetInfo {
   BuiltinVaListKind getBuiltinVaListKind() const override {
     return TargetInfo::VoidPtrBuiltinVaList;
   }
+
+  void adjust(DiagnosticsEngine &Diags, LangOptions &Opts) override {
+    TargetInfo::adjust(Diags, Opts);
+    // The static values this addresses do not apply outside of the same thread
+    // This protection is neither available nor needed
+    Opts.ThreadsafeStatics = false;
+  }
 };
 
 } // namespace targets

clang/test/CodeGenHLSL/static-local-ctor.hlsl

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-compute -emit-llvm -o - -disable-llvm-passes %s | FileCheck %s
+
+// Verify that no per variable _Init_thread instructions are emitted for non-trivial static locals
+// These would normally be emitted by the MicrosoftCXXABI, but the DirectX backend should exlude them
+// Instead, check for the guardvar oparations that should protect the constructor initialization should
+// only take place once.
+
+RWBuffer<int> buf[10];
+
+void InitBuf(RWBuffer<int> buf) {
+  for (unsigned int i = 0; i < 100; i++)
+    buf[i] = 0;
+}
+
+// CHECK-NOT: _Init_thread_epoch
+// CHECK: define internal void @"?main@@YAXXZ"
+// CHECK-NEXT: entry:
+// CHECK-NEXT: [[Tmp1:%.*]] = alloca %"class.hlsl::RWBuffer"
+// CHECK-NEXT: [[Tmp2:%.*]] = load i32, ptr
+// CHECK-NEXT: [[Tmp3:%.*]] = and i32 [[Tmp2]], 1
+// CHECK-NEXT: [[Tmp4:%.*]] = icmp eq i32 [[Tmp3]], 0
+// CHECK-NEXT: br i1 [[Tmp4]]
+// CHECK-NOT: _Init_thread_header
+// CHECK: init:
+// CHECK-NEXT: = or i32 [[Tmp2]], 1
+// CHECK-NOT: _Init_thread_footer
+
+
+[shader("compute")]
+[numthreads(1,1,1)]
+void main() {
+  // A non-trivially constructed static local will get checks to verify that it is generated just once
+  static RWBuffer<int> mybuf;
+  mybuf = buf[0];
+  InitBuf(mybuf);
+}
+