[WebAssembly] Initial WebAssembly backend

This WebAssembly backend is just a skeleton at this time and is not yet
functional.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241022 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp

@@ -0,0 +1,74 @@
+//===-- WebAssemblyFrameLowering.cpp - WebAssembly Frame Lowering ----------==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file contains the WebAssembly implementation of
+/// TargetFrameLowering class.
+///
+/// On WebAssembly, there aren't a lot of things to do here. There are no
+/// callee-saved registers to save, and no spill slots.
+///
+/// The stack grows downward.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssemblyFrameLowering.h"
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssemblyInstrInfo.h"
+#include "WebAssemblyMachineFunctionInfo.h"
+#include "WebAssemblySubtarget.h"
+#include "WebAssemblyTargetMachine.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "frame-info"
+
+// TODO: Implement a red zone?
+
+/// Return true if the specified function should have a dedicated frame pointer
+/// register.
+bool WebAssemblyFrameLowering::hasFP(const MachineFunction &MF) const {
+  llvm_unreachable("TODO: implement hasFP");
+}
+
+/// Under normal circumstances, when a frame pointer is not required, we reserve
+/// argument space for call sites in the function immediately on entry to the
+/// current function. This eliminates the need for add/sub sp brackets around
+/// call sites. Returns true if the call frame is included as part of the stack
+/// frame.
+bool WebAssemblyFrameLowering::hasReservedCallFrame(
+    const MachineFunction &MF) const {
+  return !MF.getFrameInfo()->hasVarSizedObjects();
+}
+
+void WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
+    MachineFunction &MF, MachineBasicBlock &MBB,
+    MachineBasicBlock::iterator I) const {
+  llvm_unreachable("TODO: implement eliminateCallFramePseudoInstr");
+}
+
+void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
+                                            MachineBasicBlock &MBB) const {
+  llvm_unreachable("TODO: implement emitPrologue");
+}
+
+void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
+                                            MachineBasicBlock &MBB) const {
+  llvm_unreachable("TODO: implement emitEpilogue");
+}
+
+void WebAssemblyFrameLowering::processFunctionBeforeCalleeSavedScan(
+    MachineFunction &MF, RegScavenger *RS) const {
+  llvm_unreachable("TODO: implement processFunctionBeforeCalleeSavedScan");
+}