Add attributes to functions pass (#539)

Fixes #538

* Add a new pass early in the flow to add function attributes as
necessary
  * Currently adds readnone and speculatable to
  __translate_sampler_initializer to prevent later optimizations from
  creating phis of samplers
  * add tests
* update spirv headers and tools
diff --git a/lib/AddFunctionAttributesPass.cpp b/lib/AddFunctionAttributesPass.cpp
new file mode 100644
index 0000000..95e15a8
--- /dev/null
+++ b/lib/AddFunctionAttributesPass.cpp
@@ -0,0 +1,58 @@
+// Copyright 2020 The Clspv Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+
+#include "Constants.h"
+#include "Passes.h"
+
+#define DEBUG_TYPE "addfunctionattributes"
+
+using namespace llvm;
+
+namespace {
+class AddFunctionAttributesPass : public ModulePass {
+public:
+  static char ID;
+  AddFunctionAttributesPass() : ModulePass(ID) {}
+
+  bool runOnModule(Module &M) override;
+};
+} // namespace
+
+char AddFunctionAttributesPass::ID = 0;
+INITIALIZE_PASS(AddFunctionAttributesPass, "AddFunctionAttributes",
+                "Add function attributes to builtin functions", false, false)
+
+namespace clspv {
+ModulePass *createAddFunctionAttributesPass() {
+  return new AddFunctionAttributesPass();
+}
+} // namespace clspv
+
+bool AddFunctionAttributesPass::runOnModule(Module &M) {
+  bool changed = false;
+
+  // Add ReadNone and Speculatable to literal sampler functions to avoid loop
+  // optimizations producing phis with them.
+  if (auto F = M.getFunction(clspv::TranslateSamplerInitializerFunction())) {
+    F->addFnAttr(Attribute::AttrKind::ReadNone);
+    F->addFnAttr(Attribute::AttrKind::Speculatable);
+    changed = true;
+  }
+
+  return changed;
+}