Revert "AMDGPU/GlobalISelDivergenceLowering: select divergent i1 phis" (#79274)

Reverts #78482

Author: petar-avramovic

llvm/include/llvm/CodeGen/MachineRegisterInfo.h

@@ -752,17 +752,6 @@ class MachineRegisterInfo {
   Register createVirtualRegister(const TargetRegisterClass *RegClass,
                                  StringRef Name = "");
 
-  /// All avilable attributes a virtual register can have.
-  struct RegisterAttributes {
-    const RegClassOrRegBank *RCOrRB;
-    LLT Ty;
-  };
-
-  /// createVirtualRegister - Create and return a new virtual register in the
-  /// function with the specified register attributes.
-  Register createVirtualRegister(RegisterAttributes RegAttr,
-                                 StringRef Name = "");
-
   /// Create and return a new virtual register in the function with the same
   /// attributes as the given register.
   Register cloneVirtualRegister(Register VReg, StringRef Name = "");

llvm/include/llvm/CodeGen/MachineUniformityAnalysis.h

@@ -32,25 +32,6 @@ MachineUniformityInfo computeMachineUniformityInfo(
     MachineFunction &F, const MachineCycleInfo &cycleInfo,
     const MachineDomTree &domTree, bool HasBranchDivergence);
 
-/// Legacy analysis pass which computes a \ref MachineUniformityInfo.
-class MachineUniformityAnalysisPass : public MachineFunctionPass {
-  MachineUniformityInfo UI;
-
-public:
-  static char ID;
-
-  MachineUniformityAnalysisPass();
-
-  MachineUniformityInfo &getUniformityInfo() { return UI; }
-  const MachineUniformityInfo &getUniformityInfo() const { return UI; }
-
-  bool runOnMachineFunction(MachineFunction &F) override;
-  void getAnalysisUsage(AnalysisUsage &AU) const override;
-  void print(raw_ostream &OS, const Module *M = nullptr) const override;
-
-  // TODO: verify analysis
-};
-
 } // namespace llvm
 
 #endif // LLVM_CODEGEN_MACHINEUNIFORMITYANALYSIS_H

llvm/lib/CodeGen/MachineRegisterInfo.cpp

@@ -167,17 +167,6 @@ MachineRegisterInfo::createVirtualRegister(const TargetRegisterClass *RegClass,
   return Reg;
 }
 
-/// createVirtualRegister - Create and return a new virtual register in the
-/// function with the specified register attributes.
-Register MachineRegisterInfo::createVirtualRegister(RegisterAttributes RegAttr,
-                                                    StringRef Name) {
-  Register Reg = createIncompleteVirtualRegister(Name);
-  VRegInfo[Reg].first = *RegAttr.RCOrRB;
-  setType(Reg, RegAttr.Ty);
-  noteNewVirtualRegister(Reg);
-  return Reg;
-}
-
 Register MachineRegisterInfo::cloneVirtualRegister(Register VReg,
                                                    StringRef Name) {
   Register Reg = createIncompleteVirtualRegister(Name);

llvm/lib/CodeGen/MachineUniformityAnalysis.cpp

@@ -165,6 +165,25 @@ MachineUniformityInfo llvm::computeMachineUniformityInfo(
 
 namespace {
 
+/// Legacy analysis pass which computes a \ref MachineUniformityInfo.
+class MachineUniformityAnalysisPass : public MachineFunctionPass {
+  MachineUniformityInfo UI;
+
+public:
+  static char ID;
+
+  MachineUniformityAnalysisPass();
+
+  MachineUniformityInfo &getUniformityInfo() { return UI; }
+  const MachineUniformityInfo &getUniformityInfo() const { return UI; }
+
+  bool runOnMachineFunction(MachineFunction &F) override;
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+  void print(raw_ostream &OS, const Module *M = nullptr) const override;
+
+  // TODO: verify analysis
+};
+
 class MachineUniformityInfoPrinterPass : public MachineFunctionPass {
 public:
   static char ID;

llvm/lib/Target/AMDGPU/AMDGPUGlobalISelDivergenceLowering.cpp

@@ -16,11 +16,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "AMDGPU.h"
-#include "SILowerI1Copies.h"
-#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/MachineUniformityAnalysis.h"
-#include "llvm/InitializePasses.h"
 
 #define DEBUG_TYPE "amdgpu-global-isel-divergence-lowering"
 
@@ -46,146 +42,14 @@ class AMDGPUGlobalISelDivergenceLowering : public MachineFunctionPass {
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
-    AU.addRequired<MachineDominatorTree>();
-    AU.addRequired<MachinePostDominatorTree>();
-    AU.addRequired<MachineUniformityAnalysisPass>();
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 };
 
-class DivergenceLoweringHelper : public PhiLoweringHelper {
-public:
-  DivergenceLoweringHelper(MachineFunction *MF, MachineDominatorTree *DT,
-                           MachinePostDominatorTree *PDT,
-                           MachineUniformityInfo *MUI);
-
-private:
-  MachineUniformityInfo *MUI = nullptr;
-  MachineIRBuilder B;
-  Register buildRegCopyToLaneMask(Register Reg);
-
-public:
-  void markAsLaneMask(Register DstReg) const override;
-  void getCandidatesForLowering(
-      SmallVectorImpl<MachineInstr *> &Vreg1Phis) const override;
-  void collectIncomingValuesFromPhi(
-      const MachineInstr *MI,
-      SmallVectorImpl<Incoming> &Incomings) const override;
-  void replaceDstReg(Register NewReg, Register OldReg,
-                     MachineBasicBlock *MBB) override;
-  void buildMergeLaneMasks(MachineBasicBlock &MBB,
-                           MachineBasicBlock::iterator I, const DebugLoc &DL,
-                           Register DstReg, Register PrevReg,
-                           Register CurReg) override;
-  void constrainAsLaneMask(Incoming &In) override;
-};
-
-DivergenceLoweringHelper::DivergenceLoweringHelper(
-    MachineFunction *MF, MachineDominatorTree *DT,
-    MachinePostDominatorTree *PDT, MachineUniformityInfo *MUI)
-    : PhiLoweringHelper(MF, DT, PDT), MUI(MUI), B(*MF) {}
-
-// _(s1) -> SReg_32/64(s1)
-void DivergenceLoweringHelper::markAsLaneMask(Register DstReg) const {
-  assert(MRI->getType(DstReg) == LLT::scalar(1));
-
-  if (MRI->getRegClassOrNull(DstReg)) {
-    if (MRI->constrainRegClass(DstReg, ST->getBoolRC()))
-      return;
-    llvm_unreachable("Failed to constrain register class");
-  }
-
-  MRI->setRegClass(DstReg, ST->getBoolRC());
-}
-
-void DivergenceLoweringHelper::getCandidatesForLowering(
-    SmallVectorImpl<MachineInstr *> &Vreg1Phis) const {
-  LLT S1 = LLT::scalar(1);
-
-  // Add divergent i1 phis to the list
-  for (MachineBasicBlock &MBB : *MF) {
-    for (MachineInstr &MI : MBB.phis()) {
-      Register Dst = MI.getOperand(0).getReg();
-      if (MRI->getType(Dst) == S1 && MUI->isDivergent(Dst))
-        Vreg1Phis.push_back(&MI);
-    }
-  }
-}
-
-void DivergenceLoweringHelper::collectIncomingValuesFromPhi(
-    const MachineInstr *MI, SmallVectorImpl<Incoming> &Incomings) const {
-  for (unsigned i = 1; i < MI->getNumOperands(); i += 2) {
-    Incomings.emplace_back(MI->getOperand(i).getReg(),
-                           MI->getOperand(i + 1).getMBB(), Register());
-  }
-}
-
-void DivergenceLoweringHelper::replaceDstReg(Register NewReg, Register OldReg,
-                                             MachineBasicBlock *MBB) {
-  BuildMI(*MBB, MBB->getFirstNonPHI(), {}, TII->get(AMDGPU::COPY), OldReg)
-      .addReg(NewReg);
-}
-
-// Copy Reg to new lane mask register, insert a copy after instruction that
-// defines Reg while skipping phis if needed.
-Register DivergenceLoweringHelper::buildRegCopyToLaneMask(Register Reg) {
-  Register LaneMask = createLaneMaskReg(MRI, LaneMaskRegAttrs);
-  MachineInstr *Instr = MRI->getVRegDef(Reg);
-  MachineBasicBlock *MBB = Instr->getParent();
-  B.setInsertPt(*MBB, MBB->SkipPHIsAndLabels(std::next(Instr->getIterator())));
-  B.buildCopy(LaneMask, Reg);
-  return LaneMask;
-}
-
-// bb.previous
-//   %PrevReg = ...
-//
-// bb.current
-//   %CurReg = ...
-//
-//   %DstReg - not defined
-//
-// -> (wave32 example, new registers have sreg_32 reg class and S1 LLT)
-//
-// bb.previous
-//   %PrevReg = ...
-//   %PrevRegCopy:sreg_32(s1) = COPY %PrevReg
-//
-// bb.current
-//   %CurReg = ...
-//   %CurRegCopy:sreg_32(s1) = COPY %CurReg
-//   ...
-//   %PrevMaskedReg:sreg_32(s1) = ANDN2 %PrevRegCopy, ExecReg - active lanes 0
-//   %CurMaskedReg:sreg_32(s1)  = AND %ExecReg, CurRegCopy - inactive lanes to 0
-//   %DstReg:sreg_32(s1)        = OR %PrevMaskedReg, CurMaskedReg
-//
-// DstReg = for active lanes rewrite bit in PrevReg with bit from CurReg
-void DivergenceLoweringHelper::buildMergeLaneMasks(
-    MachineBasicBlock &MBB, MachineBasicBlock::iterator I, const DebugLoc &DL,
-    Register DstReg, Register PrevReg, Register CurReg) {
-  // DstReg = (PrevReg & !EXEC) | (CurReg & EXEC)
-  // TODO: check if inputs are constants or results of a compare.
-
-  Register PrevRegCopy = buildRegCopyToLaneMask(PrevReg);
-  Register CurRegCopy = buildRegCopyToLaneMask(CurReg);
-  Register PrevMaskedReg = createLaneMaskReg(MRI, LaneMaskRegAttrs);
-  Register CurMaskedReg = createLaneMaskReg(MRI, LaneMaskRegAttrs);
-
-  B.setInsertPt(MBB, I);
-  B.buildInstr(AndN2Op, {PrevMaskedReg}, {PrevRegCopy, ExecReg});
-  B.buildInstr(AndOp, {CurMaskedReg}, {ExecReg, CurRegCopy});
-  B.buildInstr(OrOp, {DstReg}, {PrevMaskedReg, CurMaskedReg});
-}
-
-void DivergenceLoweringHelper::constrainAsLaneMask(Incoming &In) { return; }
-
 } // End anonymous namespace.
 
 INITIALIZE_PASS_BEGIN(AMDGPUGlobalISelDivergenceLowering, DEBUG_TYPE,
                       "AMDGPU GlobalISel divergence lowering", false, false)
-INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
-INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
-INITIALIZE_PASS_DEPENDENCY(MachineUniformityAnalysisPass)
 INITIALIZE_PASS_END(AMDGPUGlobalISelDivergenceLowering, DEBUG_TYPE,
                     "AMDGPU GlobalISel divergence lowering", false, false)
 
@@ -200,12 +64,5 @@ FunctionPass *llvm::createAMDGPUGlobalISelDivergenceLoweringPass() {
 
 bool AMDGPUGlobalISelDivergenceLowering::runOnMachineFunction(
     MachineFunction &MF) {
-  MachineDominatorTree &DT = getAnalysis<MachineDominatorTree>();
-  MachinePostDominatorTree &PDT = getAnalysis<MachinePostDominatorTree>();
-  MachineUniformityInfo &MUI =
-      getAnalysis<MachineUniformityAnalysisPass>().getUniformityInfo();
-
-  DivergenceLoweringHelper Helper(&MF, &DT, &PDT, &MUI);
-
-  return Helper.lowerPhis();
+  return false;
 }

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -210,7 +210,6 @@ bool AMDGPUInstructionSelector::selectCOPY(MachineInstr &I) const {
 bool AMDGPUInstructionSelector::selectPHI(MachineInstr &I) const {
   const Register DefReg = I.getOperand(0).getReg();
   const LLT DefTy = MRI->getType(DefReg);
-
   if (DefTy == LLT::scalar(1)) {
     if (!AllowRiskySelect) {
       LLVM_DEBUG(dbgs() << "Skipping risky boolean phi\n");
@@ -3553,6 +3552,8 @@ bool AMDGPUInstructionSelector::selectStackRestore(MachineInstr &MI) const {
 }
 
 bool AMDGPUInstructionSelector::select(MachineInstr &I) {
+  if (I.isPHI())
+    return selectPHI(I);
 
   if (!I.isPreISelOpcode()) {
     if (I.isCopy())
@@ -3695,8 +3696,6 @@ bool AMDGPUInstructionSelector::select(MachineInstr &I) {
     return selectWaveAddress(I);
   case AMDGPU::G_STACKRESTORE:
     return selectStackRestore(I);
-  case AMDGPU::G_PHI:
-    return selectPHI(I);
   default:
     return selectImpl(I, *CoverageInfo);
   }

llvm/lib/Target/AMDGPU/SILowerI1Copies.cpp

@@ -31,9 +31,9 @@
 
 using namespace llvm;
 
-static Register
-insertUndefLaneMask(MachineBasicBlock *MBB, MachineRegisterInfo *MRI,
-                    MachineRegisterInfo::RegisterAttributes LaneMaskRegAttrs);
+static Register insertUndefLaneMask(MachineBasicBlock *MBB,
+                                    MachineRegisterInfo *MRI,
+                                    Register LaneMaskRegAttrs);
 
 namespace {
 
@@ -78,7 +78,7 @@ class Vreg1LoweringHelper : public PhiLoweringHelper {
                            MachineBasicBlock::iterator I, const DebugLoc &DL,
                            Register DstReg, Register PrevReg,
                            Register CurReg) override;
-  void constrainAsLaneMask(Incoming &In) override;
+  void constrainIncomingRegisterTakenAsIs(Incoming &In) override;
 
   bool lowerCopiesFromI1();
   bool lowerCopiesToI1();
@@ -304,8 +304,7 @@ class LoopFinder {
   /// blocks, so that the SSA updater doesn't have to search all the way to the
   /// function entry.
   void addLoopEntries(unsigned LoopLevel, MachineSSAUpdater &SSAUpdater,
-                      MachineRegisterInfo &MRI,
-                      MachineRegisterInfo::RegisterAttributes LaneMaskRegAttrs,
+                      MachineRegisterInfo &MRI, Register LaneMaskRegAttrs,
                       ArrayRef<Incoming> Incomings = {}) {
     assert(LoopLevel < CommonDominators.size());
 
@@ -412,15 +411,14 @@ FunctionPass *llvm::createSILowerI1CopiesPass() {
   return new SILowerI1Copies();
 }
 
-Register llvm::createLaneMaskReg(
-    MachineRegisterInfo *MRI,
-    MachineRegisterInfo::RegisterAttributes LaneMaskRegAttrs) {
-  return MRI->createVirtualRegister(LaneMaskRegAttrs);
+Register llvm::createLaneMaskReg(MachineRegisterInfo *MRI,
+                                 Register LaneMaskRegAttrs) {
+  return MRI->cloneVirtualRegister(LaneMaskRegAttrs);
 }
 
-static Register
-insertUndefLaneMask(MachineBasicBlock *MBB, MachineRegisterInfo *MRI,
-                    MachineRegisterInfo::RegisterAttributes LaneMaskRegAttrs) {
+static Register insertUndefLaneMask(MachineBasicBlock *MBB,
+                                    MachineRegisterInfo *MRI,
+                                    Register LaneMaskRegAttrs) {
   MachineFunction &MF = *MBB->getParent();
   const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
   const SIInstrInfo *TII = ST.getInstrInfo();
@@ -621,7 +619,7 @@ bool PhiLoweringHelper::lowerPhis() {
       for (auto &Incoming : Incomings) {
         MachineBasicBlock &IMBB = *Incoming.Block;
         if (PIA.isSource(IMBB)) {
-          constrainAsLaneMask(Incoming);
+          constrainIncomingRegisterTakenAsIs(Incoming);
           SSAUpdater.AddAvailableValue(&IMBB, Incoming.Reg);
         } else {
           Incoming.UpdatedReg = createLaneMaskReg(MRI, LaneMaskRegAttrs);
@@ -913,4 +911,6 @@ void Vreg1LoweringHelper::buildMergeLaneMasks(MachineBasicBlock &MBB,
   }
 }
 
-void Vreg1LoweringHelper::constrainAsLaneMask(Incoming &In) {}
+void Vreg1LoweringHelper::constrainIncomingRegisterTakenAsIs(Incoming &In) {
+  return;
+}

llvm/lib/Target/AMDGPU/SILowerI1Copies.h

@@ -31,9 +31,7 @@ struct Incoming {
       : Reg(Reg), Block(Block), UpdatedReg(UpdatedReg) {}
 };
 
-Register
-createLaneMaskReg(MachineRegisterInfo *MRI,
-                  MachineRegisterInfo::RegisterAttributes LaneMaskRegAttrs);
+Register createLaneMaskReg(MachineRegisterInfo *MRI, Register LaneMaskRegAttrs);
 
 class PhiLoweringHelper {
 public:
@@ -49,7 +47,7 @@ class PhiLoweringHelper {
   MachineRegisterInfo *MRI = nullptr;
   const GCNSubtarget *ST = nullptr;
   const SIInstrInfo *TII = nullptr;
-  MachineRegisterInfo::RegisterAttributes LaneMaskRegAttrs;
+  Register LaneMaskRegAttrs;
 
 #ifndef NDEBUG
   DenseSet<Register> PhiRegisters;
@@ -70,8 +68,7 @@ class PhiLoweringHelper {
   getSaluInsertionAtEnd(MachineBasicBlock &MBB) const;
 
   void initializeLaneMaskRegisterAttributes(Register LaneMask) {
-    LaneMaskRegAttrs.RCOrRB = &MRI->getRegClassOrRegBank(LaneMask);
-    LaneMaskRegAttrs.Ty = MRI->getType(LaneMask);
+    LaneMaskRegAttrs = LaneMask;
   }
 
   bool isLaneMaskReg(Register Reg) const {
@@ -94,7 +91,7 @@ class PhiLoweringHelper {
                                    MachineBasicBlock::iterator I,
                                    const DebugLoc &DL, Register DstReg,
                                    Register PrevReg, Register CurReg) = 0;
-  virtual void constrainAsLaneMask(Incoming &In) = 0;
+  virtual void constrainIncomingRegisterTakenAsIs(Incoming &In) = 0;
 };
 
 } // end namespace llvm