1 files changed, 107 insertions, 0 deletions
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
new file mode 100644
index 000000000000..0bd30791e57c
--- /dev/null
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
@@ -0,0 +1,107 @@
+//===--- WebAssemblyOptimizeLiveIntervals.cpp - LiveInterval processing ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Optimize LiveIntervals for use in a post-RA context.
+//
+/// LiveIntervals normally runs before register allocation when the code is
+/// only recently lowered out of SSA form, so it's uncommon for registers to
+/// have multiple defs, and when they do, the defs are usually closely related.
+/// Later, after coalescing, tail duplication, and other optimizations, it's
+/// more common to see registers with multiple unrelated defs. This pass
+/// updates LiveIntervals to distribute the value numbers across separate
+/// LiveIntervals.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssembly.h"
+#include "WebAssemblySubtarget.h"
+#include "llvm/CodeGen/LiveIntervals.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-optimize-live-intervals"
+
+namespace {
+class WebAssemblyOptimizeLiveIntervals final : public MachineFunctionPass {
+  StringRef getPassName() const override {
+    return "WebAssembly Optimize Live Intervals";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<LiveIntervals>();
+    AU.addPreserved<MachineBlockFrequencyInfo>();
+    AU.addPreserved<SlotIndexes>();
+    AU.addPreserved<LiveIntervals>();
+    AU.addPreservedID(LiveVariablesID);
+    AU.addPreservedID(MachineDominatorsID);
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+public:
+  static char ID; // Pass identification, replacement for typeid
+  WebAssemblyOptimizeLiveIntervals() : MachineFunctionPass(ID) {}
+};
+} // end anonymous namespace
+
+char WebAssemblyOptimizeLiveIntervals::ID = 0;
+INITIALIZE_PASS(WebAssemblyOptimizeLiveIntervals, DEBUG_TYPE,
+                "Optimize LiveIntervals for WebAssembly", false, false)
+
+FunctionPass *llvm::createWebAssemblyOptimizeLiveIntervals() {
+  return new WebAssemblyOptimizeLiveIntervals();
+}
+
+bool WebAssemblyOptimizeLiveIntervals::runOnMachineFunction(
+    MachineFunction &MF) {
+  LLVM_DEBUG(dbgs() << "********** Optimize LiveIntervals **********\n"
+                       "********** Function: "
+                    << MF.getName() << '\n');
+
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  auto &LIS = getAnalysis<LiveIntervals>();
+
+  // We don't preserve SSA form.
+  MRI.leaveSSA();
+
+  assert(MRI.tracksLiveness() && "OptimizeLiveIntervals expects liveness");
+
+  // Split multiple-VN LiveIntervals into multiple LiveIntervals.
+  SmallVector<LiveInterval *, 4> SplitLIs;
+  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) {
+    unsigned Reg = Register::index2VirtReg(I);
+    if (MRI.reg_nodbg_empty(Reg))
+      continue;
+
+    LIS.splitSeparateComponents(LIS.getInterval(Reg), SplitLIs);
+    SplitLIs.clear();
+  }
+
+  // In PrepareForLiveIntervals, we conservatively inserted IMPLICIT_DEF
+  // instructions to satisfy LiveIntervals' requirement that all uses be
+  // dominated by defs. Now that LiveIntervals has computed which of these
+  // defs are actually needed and which are dead, remove the dead ones.
+  for (auto MII = MF.begin()->begin(), MIE = MF.begin()->end(); MII != MIE;) {
+    MachineInstr *MI = &*MII++;
+    if (MI->isImplicitDef() && MI->getOperand(0).isDead()) {
+      LiveInterval &LI = LIS.getInterval(MI->getOperand(0).getReg());
+      LIS.removeVRegDefAt(LI, LIS.getInstructionIndex(*MI).getRegSlot());
+      LIS.RemoveMachineInstrFromMaps(*MI);
+      MI->eraseFromParent();
+    }
+  }
+
+  return false;
+}