LLVM  11.0.0git
WebAssemblyOptimizeLiveIntervals.cpp
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1 //===--- WebAssemblyOptimizeLiveIntervals.cpp - LiveInterval processing ---===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 ///
9 /// \file
10 /// Optimize LiveIntervals for use in a post-RA context.
11 //
12 /// LiveIntervals normally runs before register allocation when the code is
13 /// only recently lowered out of SSA form, so it's uncommon for registers to
14 /// have multiple defs, and when they do, the defs are usually closely related.
15 /// Later, after coalescing, tail duplication, and other optimizations, it's
16 /// more common to see registers with multiple unrelated defs. This pass
17 /// updates LiveIntervals to distribute the value numbers across separate
18 /// LiveIntervals.
19 ///
20 //===----------------------------------------------------------------------===//
21 
22 #include "WebAssembly.h"
24 #include "WebAssemblySubtarget.h"
28 #include "llvm/CodeGen/Passes.h"
29 #include "llvm/Support/Debug.h"
31 using namespace llvm;
32 
33 #define DEBUG_TYPE "wasm-optimize-live-intervals"
34 
35 namespace {
36 class WebAssemblyOptimizeLiveIntervals final : public MachineFunctionPass {
37  StringRef getPassName() const override {
38  return "WebAssembly Optimize Live Intervals";
39  }
40 
41  void getAnalysisUsage(AnalysisUsage &AU) const override {
42  AU.setPreservesCFG();
50  }
51 
52  bool runOnMachineFunction(MachineFunction &MF) override;
53 
54 public:
55  static char ID; // Pass identification, replacement for typeid
56  WebAssemblyOptimizeLiveIntervals() : MachineFunctionPass(ID) {}
57 };
58 } // end anonymous namespace
59 
61 INITIALIZE_PASS(WebAssemblyOptimizeLiveIntervals, DEBUG_TYPE,
62  "Optimize LiveIntervals for WebAssembly", false, false)
63 
65  return new WebAssemblyOptimizeLiveIntervals();
66 }
67 
68 bool WebAssemblyOptimizeLiveIntervals::runOnMachineFunction(
69  MachineFunction &MF) {
70  LLVM_DEBUG(dbgs() << "********** Optimize LiveIntervals **********\n"
71  "********** Function: "
72  << MF.getName() << '\n');
73 
75  auto &LIS = getAnalysis<LiveIntervals>();
76 
77  // We don't preserve SSA form.
78  MRI.leaveSSA();
79 
80  assert(MRI.tracksLiveness() && "OptimizeLiveIntervals expects liveness");
81 
82  // Split multiple-VN LiveIntervals into multiple LiveIntervals.
84  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) {
85  unsigned Reg = Register::index2VirtReg(I);
86  auto &TRI = *MF.getSubtarget<WebAssemblySubtarget>().getRegisterInfo();
87 
88  if (MRI.reg_nodbg_empty(Reg))
89  continue;
90 
91  LIS.splitSeparateComponents(LIS.getInterval(Reg), SplitLIs);
92  if (Reg == TRI.getFrameRegister(MF) && SplitLIs.size() > 0) {
93  // The live interval for the frame register was split, resulting in a new
94  // VReg. For now we only support debug info output for a single frame base
95  // value for the function, so just use the last one. It will certainly be
96  // wrong for some part of the function, but until we are able to track
97  // values through live-range splitting and stackification, it will have to
98  // do.
99  MF.getInfo<WebAssemblyFunctionInfo>()->setFrameBaseVreg(
100  SplitLIs.back()->reg);
101  }
102  SplitLIs.clear();
103  }
104 
105  // In PrepareForLiveIntervals, we conservatively inserted IMPLICIT_DEF
106  // instructions to satisfy LiveIntervals' requirement that all uses be
107  // dominated by defs. Now that LiveIntervals has computed which of these
108  // defs are actually needed and which are dead, remove the dead ones.
109  for (auto MII = MF.begin()->begin(), MIE = MF.begin()->end(); MII != MIE;) {
110  MachineInstr *MI = &*MII++;
111  if (MI->isImplicitDef() && MI->getOperand(0).isDead()) {
112  LiveInterval &LI = LIS.getInterval(MI->getOperand(0).getReg());
113  LIS.removeVRegDefAt(LI, LIS.getInstructionIndex(*MI).getRegSlot());
114  LIS.RemoveMachineInstrFromMaps(*MI);
115  MI->eraseFromParent();
116  }
117  }
118 
119  return true;
120 }
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
char & MachineDominatorsID
MachineDominators - This pass is a machine dominators analysis pass.
LiveInterval - This class represents the liveness of a register, or stack slot.
Definition: LiveInterval.h:680
unsigned Reg
MachineBlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation to estimate machine basic b...
unsigned const TargetRegisterInfo * TRI
static unsigned index2VirtReg(unsigned Index)
Convert a 0-based index to a virtual register number.
Definition: Register.h:83
This file contains the entry points for global functions defined in the LLVM WebAssembly back-end...
AnalysisUsage & addRequired()
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
void eraseFromParent()
Unlink &#39;this&#39; from the containing basic block and delete it.
INITIALIZE_PASS(WebAssemblyOptimizeLiveIntervals, DEBUG_TYPE, "Optimize LiveIntervals for WebAssembly", false, false) FunctionPass *llvm
SlotIndexes pass.
Definition: SlotIndexes.h:314
AnalysisUsage & addPreservedID(const void *ID)
StringRef getName() const
getName - Return the name of the corresponding LLVM function.
char & LiveVariablesID
LiveVariables pass - This pass computes the set of blocks in which each variable is life and sets mac...
unsigned const MachineRegisterInfo * MRI
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
Represent the analysis usage information of a pass.
Ty * getInfo()
getInfo - Keep track of various per-function pieces of information for backends that would like to do...
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:281
bool isImplicitDef() const
This file declares the WebAssembly-specific subclass of TargetSubtarget.
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:883
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:253
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
Representation of each machine instruction.
Definition: MachineInstr.h:62
This class is derived from MachineFunctionInfo and contains private WebAssembly-specific information ...
MachineRegisterInfo & getRegInfo()
getRegInfo - Return information about the registers currently in use.
#define I(x, y, z)
Definition: MD5.cpp:59
This file declares WebAssembly-specific per-machine-function information.
FunctionPass * createWebAssemblyOptimizeLiveIntervals()
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
IRTranslator LLVM IR MI
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:57
Register getReg() const
getReg - Returns the register number.
#define LLVM_DEBUG(X)
Definition: Debug.h:122
const MachineOperand & getOperand(unsigned i) const
Definition: MachineInstr.h:437