[WebAssembly] Reintroduce ARGUMENT moving logic

[oota-llvm.git] / lib / Target / WebAssembly / WebAssemblyArgumentMove.cpp

diff --git a/lib/Target/WebAssembly/WebAssemblyArgumentMove.cpp b/lib/Target/WebAssembly/WebAssemblyArgumentMove.cpp
new file mode 100644 (file)
index 0000000..3893c40
--- /dev/null
+++ b/lib/Target/WebAssembly/WebAssemblyArgumentMove.cpp
@@ -0,0 +1,110 @@
+//===-- WebAssemblyArgumentMove.cpp - Argument instruction moving ---------===//
+//
+//                     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 moves ARGUMENT instructions after ScheduleDAG scheduling.
+///
+/// Arguments are really live-in registers, however, since we use virtual
+/// registers and LLVM doesn't support live-in virtual registers, we're
+/// currently making do with ARGUMENT instructions which are placed at the top
+/// of the entry block. The trick is to get them to *stay* at the top of the
+/// entry block.
+///
+/// The ARGUMENTS physical register keeps these instructions pinned in place
+/// during liveness-aware CodeGen passes, however one thing which does not
+/// respect this is the ScheduleDAG scheduler. This pass is therefore run
+/// immediately after that.
+///
+/// This is all hopefully a temporary solution until we find a better solution
+/// for describing the live-in nature of arguments.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssembly.h"
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssemblyMachineFunctionInfo.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-argument-move"
+
+namespace {
+class WebAssemblyArgumentMove final : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  WebAssemblyArgumentMove() : MachineFunctionPass(ID) {}
+
+  const char *getPassName() const override {
+    return "WebAssembly Argument Move";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addPreserved<MachineBlockFrequencyInfo>();
+    AU.addPreservedID(MachineDominatorsID);
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+} // end anonymous namespace
+
+char WebAssemblyArgumentMove::ID = 0;
+FunctionPass *llvm::createWebAssemblyArgumentMove() {
+  return new WebAssemblyArgumentMove();
+}
+
+/// Test whether the given instruction is an ARGUMENT.
+static bool IsArgument(const MachineInstr *MI) {
+  switch (MI->getOpcode()) {
+  case WebAssembly::ARGUMENT_I32:
+  case WebAssembly::ARGUMENT_I64:
+  case WebAssembly::ARGUMENT_F32:
+  case WebAssembly::ARGUMENT_F64:
+    return true;
+  default:
+    return false;
+  }
+}
+
+bool WebAssemblyArgumentMove::runOnMachineFunction(MachineFunction &MF) {
+  DEBUG({
+    dbgs() << "********** Argument Move **********\n"
+           << "********** Function: " << MF.getName() << '\n';
+  });
+
+  bool Changed = false;
+  MachineBasicBlock &EntryMBB = MF.front();
+  MachineBasicBlock::iterator InsertPt = EntryMBB.end();
+
+  // Look for the first NonArg instruction.
+  for (auto MII = EntryMBB.begin(), MIE = EntryMBB.end(); MII != MIE; ++MII) {
+    MachineInstr *MI = MII;
+    if (!IsArgument(MI)) {
+      InsertPt = MII;
+      break;
+    }
+  }
+
+  // Now move any argument instructions later in the block
+  // to before our first NonArg instruction.
+  for (auto I = InsertPt, E = EntryMBB.end(); I != E; ++I) {
+    MachineInstr *MI = I;
+    if (IsArgument(MI)) {
+      EntryMBB.insert(InsertPt, MI->removeFromParent());
+      Changed = true;
+    }
+  }
+
+  return Changed;
+}