forked from OSchip/llvm-project
121 lines
4.6 KiB
C++
121 lines
4.6 KiB
C++
//===--- WebAssemblyOptimizeLiveIntervals.cpp - LiveInterval processing ---===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// Optimize LiveIntervals for use in a post-RA context.
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//
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/// LiveIntervals normally runs before register allocation when the code is
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/// only recently lowered out of SSA form, so it's uncommon for registers to
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/// have multiple defs, and when they do, the defs are usually closely related.
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/// Later, after coalescing, tail duplication, and other optimizations, it's
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/// more common to see registers with multiple unrelated defs. This pass
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/// updates LiveIntervals to distribute the value numbers across separate
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/// LiveIntervals.
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///
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//===----------------------------------------------------------------------===//
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#include "WebAssembly.h"
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#include "WebAssemblyMachineFunctionInfo.h"
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#include "WebAssemblySubtarget.h"
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#include "llvm/CodeGen/LiveIntervals.h"
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#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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#define DEBUG_TYPE "wasm-optimize-live-intervals"
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namespace {
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class WebAssemblyOptimizeLiveIntervals final : public MachineFunctionPass {
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StringRef getPassName() const override {
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return "WebAssembly Optimize Live Intervals";
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<LiveIntervals>();
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AU.addPreserved<MachineBlockFrequencyInfo>();
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AU.addPreserved<SlotIndexes>();
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AU.addPreserved<LiveIntervals>();
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AU.addPreservedID(LiveVariablesID);
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AU.addPreservedID(MachineDominatorsID);
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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public:
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static char ID; // Pass identification, replacement for typeid
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WebAssemblyOptimizeLiveIntervals() : MachineFunctionPass(ID) {}
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};
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} // end anonymous namespace
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char WebAssemblyOptimizeLiveIntervals::ID = 0;
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INITIALIZE_PASS(WebAssemblyOptimizeLiveIntervals, DEBUG_TYPE,
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"Optimize LiveIntervals for WebAssembly", false, false)
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FunctionPass *llvm::createWebAssemblyOptimizeLiveIntervals() {
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return new WebAssemblyOptimizeLiveIntervals();
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}
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bool WebAssemblyOptimizeLiveIntervals::runOnMachineFunction(
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MachineFunction &MF) {
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LLVM_DEBUG(dbgs() << "********** Optimize LiveIntervals **********\n"
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"********** Function: "
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<< MF.getName() << '\n');
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MachineRegisterInfo &MRI = MF.getRegInfo();
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auto &LIS = getAnalysis<LiveIntervals>();
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// We don't preserve SSA form.
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MRI.leaveSSA();
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assert(MRI.tracksLiveness() && "OptimizeLiveIntervals expects liveness");
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// Split multiple-VN LiveIntervals into multiple LiveIntervals.
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SmallVector<LiveInterval *, 4> SplitLIs;
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for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) {
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unsigned Reg = Register::index2VirtReg(I);
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auto &TRI = *MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
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if (MRI.reg_nodbg_empty(Reg))
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continue;
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LIS.splitSeparateComponents(LIS.getInterval(Reg), SplitLIs);
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if (Reg == TRI.getFrameRegister(MF) && SplitLIs.size() > 0) {
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// The live interval for the frame register was split, resulting in a new
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// VReg. For now we only support debug info output for a single frame base
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// value for the function, so just use the last one. It will certainly be
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// wrong for some part of the function, but until we are able to track
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// values through live-range splitting and stackification, it will have to
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// do.
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MF.getInfo<WebAssemblyFunctionInfo>()->setFrameBaseVreg(
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SplitLIs.back()->reg);
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}
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SplitLIs.clear();
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}
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// In PrepareForLiveIntervals, we conservatively inserted IMPLICIT_DEF
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// instructions to satisfy LiveIntervals' requirement that all uses be
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// dominated by defs. Now that LiveIntervals has computed which of these
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// defs are actually needed and which are dead, remove the dead ones.
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for (auto MII = MF.begin()->begin(), MIE = MF.begin()->end(); MII != MIE;) {
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MachineInstr *MI = &*MII++;
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if (MI->isImplicitDef() && MI->getOperand(0).isDead()) {
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LiveInterval &LI = LIS.getInterval(MI->getOperand(0).getReg());
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LIS.removeVRegDefAt(LI, LIS.getInstructionIndex(*MI).getRegSlot());
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LIS.RemoveMachineInstrFromMaps(*MI);
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MI->eraseFromParent();
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}
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}
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return true;
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}
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