summaryrefslogtreecommitdiff
path: root/llvm/lib/CodeGen/ModuloSchedule.cpp
diff options
context:
space:
mode:
Diffstat (limited to 'llvm/lib/CodeGen/ModuloSchedule.cpp')
-rw-r--r--llvm/lib/CodeGen/ModuloSchedule.cpp217
1 files changed, 189 insertions, 28 deletions
diff --git a/llvm/lib/CodeGen/ModuloSchedule.cpp b/llvm/lib/CodeGen/ModuloSchedule.cpp
index 7ce3c5861801a..163e52d9199d1 100644
--- a/llvm/lib/CodeGen/ModuloSchedule.cpp
+++ b/llvm/lib/CodeGen/ModuloSchedule.cpp
@@ -13,6 +13,7 @@
#include "llvm/CodeGen/MachineLoopUtils.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
+#include "llvm/InitializePasses.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
@@ -1189,7 +1190,7 @@ void ModuloScheduleExpander::rewriteScheduledInstr(
bool ModuloScheduleExpander::isLoopCarried(MachineInstr &Phi) {
if (!Phi.isPHI())
return false;
- unsigned DefCycle = Schedule.getCycle(&Phi);
+ int DefCycle = Schedule.getCycle(&Phi);
int DefStage = Schedule.getStage(&Phi);
unsigned InitVal = 0;
@@ -1198,7 +1199,7 @@ bool ModuloScheduleExpander::isLoopCarried(MachineInstr &Phi) {
MachineInstr *Use = MRI.getVRegDef(LoopVal);
if (!Use || Use->isPHI())
return true;
- unsigned LoopCycle = Schedule.getCycle(Use);
+ int LoopCycle = Schedule.getCycle(Use);
int LoopStage = Schedule.getStage(Use);
return (LoopCycle > DefCycle) || (LoopStage <= DefStage);
}
@@ -1214,7 +1215,7 @@ namespace {
// Remove any dead phis in MBB. Dead phis either have only one block as input
// (in which case they are the identity) or have no uses.
void EliminateDeadPhis(MachineBasicBlock *MBB, MachineRegisterInfo &MRI,
- LiveIntervals *LIS) {
+ LiveIntervals *LIS, bool KeepSingleSrcPhi = false) {
bool Changed = true;
while (Changed) {
Changed = false;
@@ -1226,7 +1227,7 @@ void EliminateDeadPhis(MachineBasicBlock *MBB, MachineRegisterInfo &MRI,
LIS->RemoveMachineInstrFromMaps(MI);
MI.eraseFromParent();
Changed = true;
- } else if (MI.getNumExplicitOperands() == 3) {
+ } else if (!KeepSingleSrcPhi && MI.getNumExplicitOperands() == 3) {
MRI.constrainRegClass(MI.getOperand(1).getReg(),
MRI.getRegClass(MI.getOperand(0).getReg()));
MRI.replaceRegWith(MI.getOperand(0).getReg(),
@@ -1582,6 +1583,133 @@ PeelingModuloScheduleExpander::peelKernel(LoopPeelDirection LPD) {
return NewBB;
}
+void PeelingModuloScheduleExpander::filterInstructions(MachineBasicBlock *MB,
+ int MinStage) {
+ for (auto I = MB->getFirstInstrTerminator()->getReverseIterator();
+ I != std::next(MB->getFirstNonPHI()->getReverseIterator());) {
+ MachineInstr *MI = &*I++;
+ int Stage = getStage(MI);
+ if (Stage == -1 || Stage >= MinStage)
+ continue;
+
+ for (MachineOperand &DefMO : MI->defs()) {
+ SmallVector<std::pair<MachineInstr *, Register>, 4> Subs;
+ for (MachineInstr &UseMI : MRI.use_instructions(DefMO.getReg())) {
+ // Only PHIs can use values from this block by construction.
+ // Match with the equivalent PHI in B.
+ assert(UseMI.isPHI());
+ Register Reg = getEquivalentRegisterIn(UseMI.getOperand(0).getReg(),
+ MI->getParent());
+ Subs.emplace_back(&UseMI, Reg);
+ }
+ for (auto &Sub : Subs)
+ Sub.first->substituteRegister(DefMO.getReg(), Sub.second, /*SubIdx=*/0,
+ *MRI.getTargetRegisterInfo());
+ }
+ if (LIS)
+ LIS->RemoveMachineInstrFromMaps(*MI);
+ MI->eraseFromParent();
+ }
+}
+
+void PeelingModuloScheduleExpander::moveStageBetweenBlocks(
+ MachineBasicBlock *DestBB, MachineBasicBlock *SourceBB, unsigned Stage) {
+ auto InsertPt = DestBB->getFirstNonPHI();
+ DenseMap<Register, Register> Remaps;
+ for (auto I = SourceBB->getFirstNonPHI(); I != SourceBB->end();) {
+ MachineInstr *MI = &*I++;
+ if (MI->isPHI()) {
+ // This is an illegal PHI. If we move any instructions using an illegal
+ // PHI, we need to create a legal Phi
+ Register PhiR = MI->getOperand(0).getReg();
+ auto RC = MRI.getRegClass(PhiR);
+ Register NR = MRI.createVirtualRegister(RC);
+ MachineInstr *NI = BuildMI(*DestBB, DestBB->getFirstNonPHI(), DebugLoc(),
+ TII->get(TargetOpcode::PHI), NR)
+ .addReg(PhiR)
+ .addMBB(SourceBB);
+ BlockMIs[{DestBB, CanonicalMIs[MI]}] = NI;
+ CanonicalMIs[NI] = CanonicalMIs[MI];
+ Remaps[PhiR] = NR;
+ continue;
+ }
+ if (getStage(MI) != Stage)
+ continue;
+ MI->removeFromParent();
+ DestBB->insert(InsertPt, MI);
+ auto *KernelMI = CanonicalMIs[MI];
+ BlockMIs[{DestBB, KernelMI}] = MI;
+ BlockMIs.erase({SourceBB, KernelMI});
+ }
+ SmallVector<MachineInstr *, 4> PhiToDelete;
+ for (MachineInstr &MI : DestBB->phis()) {
+ assert(MI.getNumOperands() == 3);
+ MachineInstr *Def = MRI.getVRegDef(MI.getOperand(1).getReg());
+ // If the instruction referenced by the phi is moved inside the block
+ // we don't need the phi anymore.
+ if (getStage(Def) == Stage) {
+ Register PhiReg = MI.getOperand(0).getReg();
+ MRI.replaceRegWith(MI.getOperand(0).getReg(),
+ Def->getOperand(0).getReg());
+ MI.getOperand(0).setReg(PhiReg);
+ PhiToDelete.push_back(&MI);
+ }
+ }
+ for (auto *P : PhiToDelete)
+ P->eraseFromParent();
+ InsertPt = DestBB->getFirstNonPHI();
+ // Helper to clone Phi instructions into the destination block. We clone Phi
+ // greedily to avoid combinatorial explosion of Phi instructions.
+ auto clonePhi = [&](MachineInstr *Phi) {
+ MachineInstr *NewMI = MF.CloneMachineInstr(Phi);
+ DestBB->insert(InsertPt, NewMI);
+ Register OrigR = Phi->getOperand(0).getReg();
+ Register R = MRI.createVirtualRegister(MRI.getRegClass(OrigR));
+ NewMI->getOperand(0).setReg(R);
+ NewMI->getOperand(1).setReg(OrigR);
+ NewMI->getOperand(2).setMBB(*DestBB->pred_begin());
+ Remaps[OrigR] = R;
+ CanonicalMIs[NewMI] = CanonicalMIs[Phi];
+ BlockMIs[{DestBB, CanonicalMIs[Phi]}] = NewMI;
+ PhiNodeLoopIteration[NewMI] = PhiNodeLoopIteration[Phi];
+ return R;
+ };
+ for (auto I = DestBB->getFirstNonPHI(); I != DestBB->end(); ++I) {
+ for (MachineOperand &MO : I->uses()) {
+ if (!MO.isReg())
+ continue;
+ if (Remaps.count(MO.getReg()))
+ MO.setReg(Remaps[MO.getReg()]);
+ else {
+ // If we are using a phi from the source block we need to add a new phi
+ // pointing to the old one.
+ MachineInstr *Use = MRI.getUniqueVRegDef(MO.getReg());
+ if (Use && Use->isPHI() && Use->getParent() == SourceBB) {
+ Register R = clonePhi(Use);
+ MO.setReg(R);
+ }
+ }
+ }
+ }
+}
+
+Register
+PeelingModuloScheduleExpander::getPhiCanonicalReg(MachineInstr *CanonicalPhi,
+ MachineInstr *Phi) {
+ unsigned distance = PhiNodeLoopIteration[Phi];
+ MachineInstr *CanonicalUse = CanonicalPhi;
+ for (unsigned I = 0; I < distance; ++I) {
+ assert(CanonicalUse->isPHI());
+ assert(CanonicalUse->getNumOperands() == 5);
+ unsigned LoopRegIdx = 3, InitRegIdx = 1;
+ if (CanonicalUse->getOperand(2).getMBB() == CanonicalUse->getParent())
+ std::swap(LoopRegIdx, InitRegIdx);
+ CanonicalUse =
+ MRI.getVRegDef(CanonicalUse->getOperand(LoopRegIdx).getReg());
+ }
+ return CanonicalUse->getOperand(0).getReg();
+}
+
void PeelingModuloScheduleExpander::peelPrologAndEpilogs() {
BitVector LS(Schedule.getNumStages(), true);
BitVector AS(Schedule.getNumStages(), true);
@@ -1604,26 +1732,45 @@ void PeelingModuloScheduleExpander::peelPrologAndEpilogs() {
// property that any value deffed in BB but used outside of BB is used by a
// PHI in the exiting block.
MachineBasicBlock *ExitingBB = CreateLCSSAExitingBlock();
-
+ EliminateDeadPhis(ExitingBB, MRI, LIS, /*KeepSingleSrcPhi=*/true);
// Push out the epilogs, again in reverse order.
// We can't assume anything about the minumum loop trip count at this point,
- // so emit a fairly complex epilog:
- // K[0, 1, 2] // Kernel runs stages 0, 1, 2
- // E0[2] <- P1 // Epilog runs stage 2 only, so the state after is [0].
- // E1[1, 2] <- P0 // Epilog 1 moves the last item from stage 0 to stage 2.
- //
- // This creates a single-successor single-predecessor sequence of blocks for
- // each epilog, which are kept this way for simplicity at this stage and
- // cleaned up by the optimizer later.
+ // so emit a fairly complex epilog.
+
+ // We first peel number of stages minus one epilogue. Then we remove dead
+ // stages and reorder instructions based on their stage. If we have 3 stages
+ // we generate first:
+ // E0[3, 2, 1]
+ // E1[3', 2']
+ // E2[3'']
+ // And then we move instructions based on their stages to have:
+ // E0[3]
+ // E1[2, 3']
+ // E2[1, 2', 3'']
+ // The transformation is legal because we only move instructions past
+ // instructions of a previous loop iteration.
for (int I = 1; I <= Schedule.getNumStages() - 1; ++I) {
- Epilogs.push_back(nullptr);
- for (int J = Schedule.getNumStages() - 1; J >= I; --J) {
- LS.reset();
- LS[J] = 1;
- Epilogs.back() = peelKernel(LPD_Back);
- LiveStages[Epilogs.back()] = LS;
- AvailableStages[Epilogs.back()] = AS;
+ Epilogs.push_back(peelKernel(LPD_Back));
+ MachineBasicBlock *B = Epilogs.back();
+ filterInstructions(B, Schedule.getNumStages() - I);
+ // Keep track at which iteration each phi belongs to. We need it to know
+ // what version of the variable to use during prologue/epilogue stitching.
+ EliminateDeadPhis(B, MRI, LIS, /*KeepSingleSrcPhi=*/true);
+ for (auto Phi = B->begin(), IE = B->getFirstNonPHI(); Phi != IE; ++Phi)
+ PhiNodeLoopIteration[&*Phi] = Schedule.getNumStages() - I;
+ }
+ for (size_t I = 0; I < Epilogs.size(); I++) {
+ LS.reset();
+ for (size_t J = I; J < Epilogs.size(); J++) {
+ int Iteration = J;
+ unsigned Stage = Schedule.getNumStages() - 1 + I - J;
+ // Move stage one block at a time so that Phi nodes are updated correctly.
+ for (size_t K = Iteration; K > I; K--)
+ moveStageBetweenBlocks(Epilogs[K - 1], Epilogs[K], Stage);
+ LS[Stage] = 1;
}
+ LiveStages[Epilogs[I]] = LS;
+ AvailableStages[Epilogs[I]] = AS;
}
// Now we've defined all the prolog and epilog blocks as a fallthrough
@@ -1638,8 +1785,16 @@ void PeelingModuloScheduleExpander::peelPrologAndEpilogs() {
for (MachineInstr &MI : (*EI)->phis()) {
Register Reg = MI.getOperand(1).getReg();
MachineInstr *Use = MRI.getUniqueVRegDef(Reg);
- if (Use && Use->getParent() == Pred)
+ if (Use && Use->getParent() == Pred) {
+ MachineInstr *CanonicalUse = CanonicalMIs[Use];
+ if (CanonicalUse->isPHI()) {
+ // If the use comes from a phi we need to skip as many phi as the
+ // distance between the epilogue and the kernel. Trace through the phi
+ // chain to find the right value.
+ Reg = getPhiCanonicalReg(CanonicalUse, Use);
+ }
Reg = getEquivalentRegisterIn(Reg, *PI);
+ }
MI.addOperand(MachineOperand::CreateReg(Reg, /*isDef=*/false));
MI.addOperand(MachineOperand::CreateMBB(*PI));
}
@@ -1659,6 +1814,13 @@ void PeelingModuloScheduleExpander::peelPrologAndEpilogs() {
rewriteUsesOf(MI);
}
}
+ for (auto *MI : IllegalPhisToDelete) {
+ if (LIS)
+ LIS->RemoveMachineInstrFromMaps(*MI);
+ MI->eraseFromParent();
+ }
+ IllegalPhisToDelete.clear();
+
// Now all remapping has been done, we're free to optimize the generated code.
for (MachineBasicBlock *B : reverse(Blocks))
EliminateDeadPhis(B, MRI, LIS);
@@ -1727,9 +1889,10 @@ void PeelingModuloScheduleExpander::rewriteUsesOf(MachineInstr *MI) {
R = MI->getOperand(1).getReg();
MRI.setRegClass(R, MRI.getRegClass(PhiR));
MRI.replaceRegWith(PhiR, R);
- if (LIS)
- LIS->RemoveMachineInstrFromMaps(*MI);
- MI->eraseFromParent();
+ // Postpone deleting the Phi as it may be referenced by BlockMIs and used
+ // later to figure out how to remap registers.
+ MI->getOperand(0).setReg(PhiR);
+ IllegalPhisToDelete.push_back(MI);
return;
}
@@ -1759,10 +1922,6 @@ void PeelingModuloScheduleExpander::rewriteUsesOf(MachineInstr *MI) {
}
void PeelingModuloScheduleExpander::fixupBranches() {
- std::unique_ptr<TargetInstrInfo::PipelinerLoopInfo> Info =
- TII->analyzeLoopForPipelining(BB);
- assert(Info);
-
// Work outwards from the kernel.
bool KernelDisposed = false;
int TC = Schedule.getNumStages() - 1;
@@ -1818,6 +1977,8 @@ void PeelingModuloScheduleExpander::expand() {
BB = Schedule.getLoop()->getTopBlock();
Preheader = Schedule.getLoop()->getLoopPreheader();
LLVM_DEBUG(Schedule.dump());
+ Info = TII->analyzeLoopForPipelining(BB);
+ assert(Info);
rewriteKernel();
peelPrologAndEpilogs();
generated by cgit v1.2.3 (git 2.25.1) at 2025-10-31 13:23:30 +0000