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llvm-project/llvm/lib/CodeGen/RDFLiveness.cpp

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//===- RDFLiveness.cpp ----------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Computation of the liveness information from the data-flow graph.
//
// The main functionality of this code is to compute block live-in
// information. With the live-in information in place, the placement
// of kill flags can also be recalculated.
//
// The block live-in calculation is based on the ideas from the following
// publication:
//
// Dibyendu Das, Ramakrishna Upadrasta, Benoit Dupont de Dinechin.
// "Efficient Liveness Computation Using Merge Sets and DJ-Graphs."
// ACM Transactions on Architecture and Code Optimization, Association for
// Computing Machinery, 2012, ACM TACO Special Issue on "High-Performance
// and Embedded Architectures and Compilers", 8 (4),
// <10.1145/2086696.2086706>. <hal-00647369>
//
#include "llvm/CodeGen/RDFLiveness.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineDominanceFrontier.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/RDFGraph.h"
#include "llvm/CodeGen/RDFRegisters.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <map>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace llvm;
using namespace rdf;
static cl::opt<unsigned> MaxRecNest("rdf-liveness-max-rec", cl::init(25),
cl::Hidden, cl::desc("Maximum recursion level"));
namespace llvm {
namespace rdf {
raw_ostream &operator<< (raw_ostream &OS, const Print<Liveness::RefMap> &P) {
OS << '{';
for (auto &I : P.Obj) {
OS << ' ' << printReg(I.first, &P.G.getTRI()) << '{';
for (auto J = I.second.begin(), E = I.second.end(); J != E; ) {
OS << Print<NodeId>(J->first, P.G) << PrintLaneMaskOpt(J->second);
if (++J != E)
OS << ',';
}
OS << '}';
}
OS << " }";
return OS;
}
} // end namespace rdf
} // end namespace llvm
// The order in the returned sequence is the order of reaching defs in the
// upward traversal: the first def is the closest to the given reference RefA,
// the next one is further up, and so on.
// The list ends at a reaching phi def, or when the reference from RefA is
// covered by the defs in the list (see FullChain).
// This function provides two modes of operation:
// (1) Returning the sequence of reaching defs for a particular reference
// node. This sequence will terminate at the first phi node [1].
// (2) Returning a partial sequence of reaching defs, where the final goal
// is to traverse past phi nodes to the actual defs arising from the code
// itself.
// In mode (2), the register reference for which the search was started
// may be different from the reference node RefA, for which this call was
// made, hence the argument RefRR, which holds the original register.
// Also, some definitions may have already been encountered in a previous
// call that will influence register covering. The register references
// already defined are passed in through DefRRs.
// In mode (1), the "continuation" considerations do not apply, and the
// RefRR is the same as the register in RefA, and the set DefRRs is empty.
//
// [1] It is possible for multiple phi nodes to be included in the returned
// sequence:
// SubA = phi ...
// SubB = phi ...
// ... = SuperAB(rdef:SubA), SuperAB"(rdef:SubB)
// However, these phi nodes are independent from one another in terms of
// the data-flow.
NodeList Liveness::getAllReachingDefs(RegisterRef RefRR,
NodeAddr<RefNode*> RefA, bool TopShadows, bool FullChain,
const RegisterAggr &DefRRs) {
NodeList RDefs; // Return value.
SetVector<NodeId> DefQ;
DenseMap<MachineInstr*, uint32_t> OrdMap;
// Dead defs will be treated as if they were live, since they are actually
// on the data-flow path. They cannot be ignored because even though they
// do not generate meaningful values, they still modify registers.
// If the reference is undefined, there is nothing to do.
if (RefA.Addr->getFlags() & NodeAttrs::Undef)
return RDefs;
// The initial queue should not have reaching defs for shadows. The
// whole point of a shadow is that it will have a reaching def that
// is not aliased to the reaching defs of the related shadows.
NodeId Start = RefA.Id;
auto SNA = DFG.addr<RefNode*>(Start);
if (NodeId RD = SNA.Addr->getReachingDef())
DefQ.insert(RD);
if (TopShadows) {
for (auto S : DFG.getRelatedRefs(RefA.Addr->getOwner(DFG), RefA))
if (NodeId RD = NodeAddr<RefNode*>(S).Addr->getReachingDef())
DefQ.insert(RD);
}
// Collect all the reaching defs, going up until a phi node is encountered,
// or there are no more reaching defs. From this set, the actual set of
// reaching defs will be selected.
// The traversal upwards must go on until a covering def is encountered.
// It is possible that a collection of non-covering (individually) defs
// will be sufficient, but keep going until a covering one is found.
for (unsigned i = 0; i < DefQ.size(); ++i) {
auto TA = DFG.addr<DefNode*>(DefQ[i]);
if (TA.Addr->getFlags() & NodeAttrs::PhiRef)
continue;
// Stop at the covering/overwriting def of the initial register reference.
RegisterRef RR = TA.Addr->getRegRef(DFG);
if (!DFG.IsPreservingDef(TA))
if (RegisterAggr::isCoverOf(RR, RefRR, PRI))
continue;
// Get the next level of reaching defs. This will include multiple
// reaching defs for shadows.
for (auto S : DFG.getRelatedRefs(TA.Addr->getOwner(DFG), TA))
if (NodeId RD = NodeAddr<RefNode*>(S).Addr->getReachingDef())
DefQ.insert(RD);
// Don't visit sibling defs. They share the same reaching def (which
// will be visited anyway), but they define something not aliased to
// this ref.
}
// Return the MachineBasicBlock containing a given instruction.
auto Block = [this] (NodeAddr<InstrNode*> IA) -> MachineBasicBlock* {
if (IA.Addr->getKind() == NodeAttrs::Stmt)
return NodeAddr<StmtNode*>(IA).Addr->getCode()->getParent();
assert(IA.Addr->getKind() == NodeAttrs::Phi);
NodeAddr<PhiNode*> PA = IA;
NodeAddr<BlockNode*> BA = PA.Addr->getOwner(DFG);
return BA.Addr->getCode();
};
SmallSet<NodeId,32> Defs;
// Remove all non-phi defs that are not aliased to RefRR, and separate
// the the remaining defs into buckets for containing blocks.
std::map<NodeId, NodeAddr<InstrNode*>> Owners;
std::map<MachineBasicBlock*, SmallVector<NodeId,32>> Blocks;
for (NodeId N : DefQ) {
auto TA = DFG.addr<DefNode*>(N);
bool IsPhi = TA.Addr->getFlags() & NodeAttrs::PhiRef;
if (!IsPhi && !PRI.alias(RefRR, TA.Addr->getRegRef(DFG)))
continue;
Defs.insert(TA.Id);
NodeAddr<InstrNode*> IA = TA.Addr->getOwner(DFG);
Owners[TA.Id] = IA;
Blocks[Block(IA)].push_back(IA.Id);
}
auto Precedes = [this,&OrdMap] (NodeId A, NodeId B) {
if (A == B)
return false;
NodeAddr<InstrNode*> OA = DFG.addr<InstrNode*>(A);
NodeAddr<InstrNode*> OB = DFG.addr<InstrNode*>(B);
bool StmtA = OA.Addr->getKind() == NodeAttrs::Stmt;
bool StmtB = OB.Addr->getKind() == NodeAttrs::Stmt;
if (StmtA && StmtB) {
const MachineInstr *InA = NodeAddr<StmtNode*>(OA).Addr->getCode();
const MachineInstr *InB = NodeAddr<StmtNode*>(OB).Addr->getCode();
assert(InA->getParent() == InB->getParent());
auto FA = OrdMap.find(InA);
if (FA != OrdMap.end())
return FA->second < OrdMap.find(InB)->second;
const MachineBasicBlock *BB = InA->getParent();
for (auto It = BB->begin(), E = BB->end(); It != E; ++It) {
if (It == InA->getIterator())
return true;
if (It == InB->getIterator())
return false;
}
llvm_unreachable("InA and InB should be in the same block");
}
// One of them is a phi node.
if (!StmtA && !StmtB) {
// Both are phis, which are unordered. Break the tie by id numbers.
return A < B;
}
// Only one of them is a phi. Phis always precede statements.
return !StmtA;
};
auto GetOrder = [&OrdMap] (MachineBasicBlock &B) {
uint32_t Pos = 0;
for (MachineInstr &In : B)
OrdMap.insert({&In, ++Pos});
};
// For each block, sort the nodes in it.
std::vector<MachineBasicBlock*> TmpBB;
for (auto &Bucket : Blocks) {
TmpBB.push_back(Bucket.first);
if (Bucket.second.size() > 2)
GetOrder(*Bucket.first);
llvm::sort(Bucket.second, Precedes);
}
// Sort the blocks with respect to dominance.
llvm::sort(TmpBB,
[this](auto A, auto B) { return MDT.properlyDominates(A, B); });
std::vector<NodeId> TmpInst;
for (MachineBasicBlock *MBB : llvm::reverse(TmpBB)) {
auto &Bucket = Blocks[MBB];
TmpInst.insert(TmpInst.end(), Bucket.rbegin(), Bucket.rend());
}
// The vector is a list of instructions, so that defs coming from
// the same instruction don't need to be artificially ordered.
// Then, when computing the initial segment, and iterating over an
// instruction, pick the defs that contribute to the covering (i.e. is
// not covered by previously added defs). Check the defs individually,
// i.e. first check each def if is covered or not (without adding them
// to the tracking set), and then add all the selected ones.
// The reason for this is this example:
// *d1<A>, *d2<B>, ... Assume A and B are aliased (can happen in phi nodes).
// *d3<C> If A \incl BuC, and B \incl AuC, then *d2 would be
// covered if we added A first, and A would be covered
// if we added B first.
// In this example we want both A and B, because we don't want to give
// either one priority over the other, since they belong to the same
// statement.
RegisterAggr RRs(DefRRs);
auto DefInSet = [&Defs] (NodeAddr<RefNode*> TA) -> bool {
return TA.Addr->getKind() == NodeAttrs::Def &&
Defs.count(TA.Id);
};
for (NodeId T : TmpInst) {
if (!FullChain && RRs.hasCoverOf(RefRR))
break;
auto TA = DFG.addr<InstrNode*>(T);
bool IsPhi = DFG.IsCode<NodeAttrs::Phi>(TA);
NodeList Ds;
for (NodeAddr<DefNode*> DA : TA.Addr->members_if(DefInSet, DFG)) {
RegisterRef QR = DA.Addr->getRegRef(DFG);
// Add phi defs even if they are covered by subsequent defs. This is
// for cases where the reached use is not covered by any of the defs
// encountered so far: the phi def is needed to expose the liveness
// of that use to the entry of the block.
// Example:
// phi d1<R3>(,d2,), ... Phi def d1 is covered by d2.
// d2<R3>(d1,,u3), ...
// ..., u3<D1>(d2) This use needs to be live on entry.
if (FullChain || IsPhi || !RRs.hasCoverOf(QR))
Ds.push_back(DA);
}
llvm::append_range(RDefs, Ds);
for (NodeAddr<DefNode*> DA : Ds) {
// When collecting a full chain of definitions, do not consider phi
// defs to actually define a register.
uint16_t Flags = DA.Addr->getFlags();
if (!FullChain || !(Flags & NodeAttrs::PhiRef))
if (!(Flags & NodeAttrs::Preserving)) // Don't care about Undef here.
RRs.insert(DA.Addr->getRegRef(DFG));
}
}
auto DeadP = [](const NodeAddr<DefNode*> DA) -> bool {
return DA.Addr->getFlags() & NodeAttrs::Dead;
};
llvm::erase_if(RDefs, DeadP);
return RDefs;
}
std::pair<NodeSet,bool>
Liveness::getAllReachingDefsRec(RegisterRef RefRR, NodeAddr<RefNode*> RefA,
NodeSet &Visited, const NodeSet &Defs) {
return getAllReachingDefsRecImpl(RefRR, RefA, Visited, Defs, 0, MaxRecNest);
}
std::pair<NodeSet,bool>
Liveness::getAllReachingDefsRecImpl(RegisterRef RefRR, NodeAddr<RefNode*> RefA,
NodeSet &Visited, const NodeSet &Defs, unsigned Nest, unsigned MaxNest) {
if (Nest > MaxNest)
return { NodeSet(), false };
// Collect all defined registers. Do not consider phis to be defining
// anything, only collect "real" definitions.
RegisterAggr DefRRs(PRI);
for (NodeId D : Defs) {
const auto DA = DFG.addr<const DefNode*>(D);
if (!(DA.Addr->getFlags() & NodeAttrs::PhiRef))
DefRRs.insert(DA.Addr->getRegRef(DFG));
}
NodeList RDs = getAllReachingDefs(RefRR, RefA, false, true, DefRRs);
if (RDs.empty())
return { Defs, true };
// Make a copy of the preexisting definitions and add the newly found ones.
NodeSet TmpDefs = Defs;
for (NodeAddr<NodeBase*> R : RDs)
TmpDefs.insert(R.Id);
NodeSet Result = Defs;
for (NodeAddr<DefNode*> DA : RDs) {
Result.insert(DA.Id);
if (!(DA.Addr->getFlags() & NodeAttrs::PhiRef))
continue;
NodeAddr<PhiNode*> PA = DA.Addr->getOwner(DFG);
if (!Visited.insert(PA.Id).second)
continue;
// Go over all phi uses and get the reaching defs for each use.
for (auto U : PA.Addr->members_if(DFG.IsRef<NodeAttrs::Use>, DFG)) {
const auto &T = getAllReachingDefsRecImpl(RefRR, U, Visited, TmpDefs,
Nest+1, MaxNest);
if (!T.second)
return { T.first, false };
Result.insert(T.first.begin(), T.first.end());
}
}
return { Result, true };
}
/// Find the nearest ref node aliased to RefRR, going upwards in the data
/// flow, starting from the instruction immediately preceding Inst.
NodeAddr<RefNode*> Liveness::getNearestAliasedRef(RegisterRef RefRR,
NodeAddr<InstrNode*> IA) {
NodeAddr<BlockNode*> BA = IA.Addr->getOwner(DFG);
NodeList Ins = BA.Addr->members(DFG);
NodeId FindId = IA.Id;
auto E = Ins.rend();
auto B = std::find_if(Ins.rbegin(), E,
[FindId] (const NodeAddr<InstrNode*> T) {
return T.Id == FindId;
});
// Do not scan IA (which is what B would point to).
if (B != E)
++B;
do {
// Process the range of instructions from B to E.
for (NodeAddr<InstrNode*> I : make_range(B, E)) {
NodeList Refs = I.Addr->members(DFG);
NodeAddr<RefNode*> Clob, Use;
// Scan all the refs in I aliased to RefRR, and return the one that
// is the closest to the output of I, i.e. def > clobber > use.
for (NodeAddr<RefNode*> R : Refs) {
if (!PRI.alias(R.Addr->getRegRef(DFG), RefRR))
continue;
if (DFG.IsDef(R)) {
// If it's a non-clobbering def, just return it.
if (!(R.Addr->getFlags() & NodeAttrs::Clobbering))
return R;
Clob = R;
} else {
Use = R;
}
}
if (Clob.Id != 0)
return Clob;
if (Use.Id != 0)
return Use;
}
// Go up to the immediate dominator, if any.
MachineBasicBlock *BB = BA.Addr->getCode();
BA = NodeAddr<BlockNode*>();
if (MachineDomTreeNode *N = MDT.getNode(BB)) {
if ((N = N->getIDom()))
BA = DFG.findBlock(N->getBlock());
}
if (!BA.Id)
break;
Ins = BA.Addr->members(DFG);
B = Ins.rbegin();
E = Ins.rend();
} while (true);
return NodeAddr<RefNode*>();
}
NodeSet Liveness::getAllReachedUses(RegisterRef RefRR,
NodeAddr<DefNode*> DefA, const RegisterAggr &DefRRs) {
NodeSet Uses;
// If the original register is already covered by all the intervening
// defs, no more uses can be reached.
if (DefRRs.hasCoverOf(RefRR))
return Uses;
// Add all directly reached uses.
// If the def is dead, it does not provide a value for any use.
bool IsDead = DefA.Addr->getFlags() & NodeAttrs::Dead;
NodeId U = !IsDead ? DefA.Addr->getReachedUse() : 0;
while (U != 0) {
auto UA = DFG.addr<UseNode*>(U);
if (!(UA.Addr->getFlags() & NodeAttrs::Undef)) {
RegisterRef UR = UA.Addr->getRegRef(DFG);
if (PRI.alias(RefRR, UR) && !DefRRs.hasCoverOf(UR))
Uses.insert(U);
}
U = UA.Addr->getSibling();
}
// Traverse all reached defs. This time dead defs cannot be ignored.
for (NodeId D = DefA.Addr->getReachedDef(), NextD; D != 0; D = NextD) {
auto DA = DFG.addr<DefNode*>(D);
NextD = DA.Addr->getSibling();
RegisterRef DR = DA.Addr->getRegRef(DFG);
// If this def is already covered, it cannot reach anything new.
// Similarly, skip it if it is not aliased to the interesting register.
if (DefRRs.hasCoverOf(DR) || !PRI.alias(RefRR, DR))
continue;
NodeSet T;
if (DFG.IsPreservingDef(DA)) {
// If it is a preserving def, do not update the set of intervening defs.
T = getAllReachedUses(RefRR, DA, DefRRs);
} else {
RegisterAggr NewDefRRs = DefRRs;
NewDefRRs.insert(DR);
T = getAllReachedUses(RefRR, DA, NewDefRRs);
}
Uses.insert(T.begin(), T.end());
}
return Uses;
}
void Liveness::computePhiInfo() {
RealUseMap.clear();
NodeList Phis;
NodeAddr<FuncNode*> FA = DFG.getFunc();
NodeList Blocks = FA.Addr->members(DFG);
for (NodeAddr<BlockNode*> BA : Blocks) {
auto Ps = BA.Addr->members_if(DFG.IsCode<NodeAttrs::Phi>, DFG);
llvm::append_range(Phis, Ps);
}
// phi use -> (map: reaching phi -> set of registers defined in between)
std::map<NodeId,std::map<NodeId,RegisterAggr>> PhiUp;
std::vector<NodeId> PhiUQ; // Work list of phis for upward propagation.
std::unordered_map<NodeId,RegisterAggr> PhiDRs; // Phi -> registers defined by it.
// Go over all phis.
for (NodeAddr<PhiNode*> PhiA : Phis) {
// Go over all defs and collect the reached uses that are non-phi uses
// (i.e. the "real uses").
RefMap &RealUses = RealUseMap[PhiA.Id];
NodeList PhiRefs = PhiA.Addr->members(DFG);
// Have a work queue of defs whose reached uses need to be found.
// For each def, add to the queue all reached (non-phi) defs.
SetVector<NodeId> DefQ;
NodeSet PhiDefs;
RegisterAggr DRs(PRI);
for (NodeAddr<RefNode*> R : PhiRefs) {
if (!DFG.IsRef<NodeAttrs::Def>(R))
continue;
DRs.insert(R.Addr->getRegRef(DFG));
DefQ.insert(R.Id);
PhiDefs.insert(R.Id);
}
PhiDRs.insert(std::make_pair(PhiA.Id, DRs));
// Collect the super-set of all possible reached uses. This set will
// contain all uses reached from this phi, either directly from the
// phi defs, or (recursively) via non-phi defs reached by the phi defs.
// This set of uses will later be trimmed to only contain these uses that
// are actually reached by the phi defs.
for (unsigned i = 0; i < DefQ.size(); ++i) {
NodeAddr<DefNode*> DA = DFG.addr<DefNode*>(DefQ[i]);
// Visit all reached uses. Phi defs should not really have the "dead"
// flag set, but check it anyway for consistency.
bool IsDead = DA.Addr->getFlags() & NodeAttrs::Dead;
NodeId UN = !IsDead ? DA.Addr->getReachedUse() : 0;
while (UN != 0) {
NodeAddr<UseNode*> A = DFG.addr<UseNode*>(UN);
uint16_t F = A.Addr->getFlags();
if ((F & (NodeAttrs::Undef | NodeAttrs::PhiRef)) == 0) {
RegisterRef R = A.Addr->getRegRef(DFG);
RealUses[R.Reg].insert({A.Id,R.Mask});
}
UN = A.Addr->getSibling();
}
// Visit all reached defs, and add them to the queue. These defs may
// override some of the uses collected here, but that will be handled
// later.
NodeId DN = DA.Addr->getReachedDef();
while (DN != 0) {
NodeAddr<DefNode*> A = DFG.addr<DefNode*>(DN);
for (auto T : DFG.getRelatedRefs(A.Addr->getOwner(DFG), A)) {
uint16_t Flags = NodeAddr<DefNode*>(T).Addr->getFlags();
// Must traverse the reached-def chain. Consider:
// def(D0) -> def(R0) -> def(R0) -> use(D0)
// The reachable use of D0 passes through a def of R0.
if (!(Flags & NodeAttrs::PhiRef))
DefQ.insert(T.Id);
}
DN = A.Addr->getSibling();
}
}
// Filter out these uses that appear to be reachable, but really
// are not. For example:
//
// R1:0 = d1
// = R1:0 u2 Reached by d1.
// R0 = d3
// = R1:0 u4 Still reached by d1: indirectly through
// the def d3.
// R1 = d5
// = R1:0 u6 Not reached by d1 (covered collectively
// by d3 and d5), but following reached
// defs and uses from d1 will lead here.
for (auto UI = RealUses.begin(), UE = RealUses.end(); UI != UE; ) {
// For each reached register UI->first, there is a set UI->second, of
// uses of it. For each such use, check if it is reached by this phi,
// i.e. check if the set of its reaching uses intersects the set of
// this phi's defs.
NodeRefSet Uses = UI->second;
UI->second.clear();
for (std::pair<NodeId,LaneBitmask> I : Uses) {
auto UA = DFG.addr<UseNode*>(I.first);
// Undef flag is checked above.
assert((UA.Addr->getFlags() & NodeAttrs::Undef) == 0);
RegisterRef R(UI->first, I.second);
// Calculate the exposed part of the reached use.
RegisterAggr Covered(PRI);
for (NodeAddr<DefNode*> DA : getAllReachingDefs(R, UA)) {
if (PhiDefs.count(DA.Id))
break;
Covered.insert(DA.Addr->getRegRef(DFG));
}
if (RegisterRef RC = Covered.clearIn(R)) {
// We are updating the map for register UI->first, so we need
// to map RC to be expressed in terms of that register.
RegisterRef S = PRI.mapTo(RC, UI->first);
UI->second.insert({I.first, S.Mask});
}
}
UI = UI->second.empty() ? RealUses.erase(UI) : std::next(UI);
}
// If this phi reaches some "real" uses, add it to the queue for upward
// propagation.
if (!RealUses.empty())
PhiUQ.push_back(PhiA.Id);
// Go over all phi uses and check if the reaching def is another phi.
// Collect the phis that are among the reaching defs of these uses.
// While traversing the list of reaching defs for each phi use, accumulate
// the set of registers defined between this phi (PhiA) and the owner phi
// of the reaching def.
NodeSet SeenUses;
for (auto I : PhiRefs) {
if (!DFG.IsRef<NodeAttrs::Use>(I) || SeenUses.count(I.Id))
continue;
NodeAddr<PhiUseNode*> PUA = I;
if (PUA.Addr->getReachingDef() == 0)
continue;
RegisterRef UR = PUA.Addr->getRegRef(DFG);
NodeList Ds = getAllReachingDefs(UR, PUA, true, false, NoRegs);
RegisterAggr DefRRs(PRI);
for (NodeAddr<DefNode*> D : Ds) {
if (D.Addr->getFlags() & NodeAttrs::PhiRef) {
NodeId RP = D.Addr->getOwner(DFG).Id;
std::map<NodeId,RegisterAggr> &M = PhiUp[PUA.Id];
auto F = M.find(RP);
if (F == M.end())
M.insert(std::make_pair(RP, DefRRs));
else
F->second.insert(DefRRs);
}
DefRRs.insert(D.Addr->getRegRef(DFG));
}
for (NodeAddr<PhiUseNode*> T : DFG.getRelatedRefs(PhiA, PUA))
SeenUses.insert(T.Id);
}
}
if (Trace) {
dbgs() << "Phi-up-to-phi map with intervening defs:\n";
for (auto I : PhiUp) {
dbgs() << "phi " << Print<NodeId>(I.first, DFG) << " -> {";
for (auto R : I.second)
dbgs() << ' ' << Print<NodeId>(R.first, DFG)
<< Print<RegisterAggr>(R.second, DFG);
dbgs() << " }\n";
}
}
// Propagate the reached registers up in the phi chain.
//
// The following type of situation needs careful handling:
//
// phi d1<R1:0> (1)
// |
// ... d2<R1>
// |
// phi u3<R1:0> (2)
// |
// ... u4<R1>
//
// The phi node (2) defines a register pair R1:0, and reaches a "real"
// use u4 of just R1. The same phi node is also known to reach (upwards)
// the phi node (1). However, the use u4 is not reached by phi (1),
// because of the intervening definition d2 of R1. The data flow between
// phis (1) and (2) is restricted to R1:0 minus R1, i.e. R0.
//
// When propagating uses up the phi chains, get the all reaching defs
// for a given phi use, and traverse the list until the propagated ref
// is covered, or until reaching the final phi. Only assume that the
// reference reaches the phi in the latter case.
// The operation "clearIn" can be expensive. For a given set of intervening
// defs, cache the result of subtracting these defs from a given register
// ref.
using SubMap = std::unordered_map<RegisterRef, RegisterRef>;
std::unordered_map<RegisterAggr, SubMap> Subs;
auto ClearIn = [] (RegisterRef RR, const RegisterAggr &Mid, SubMap &SM) {
if (Mid.empty())
return RR;
auto F = SM.find(RR);
if (F != SM.end())
return F->second;
RegisterRef S = Mid.clearIn(RR);
SM.insert({RR, S});
return S;
};
// Go over all phis.
for (unsigned i = 0; i < PhiUQ.size(); ++i) {
auto PA = DFG.addr<PhiNode*>(PhiUQ[i]);
NodeList PUs = PA.Addr->members_if(DFG.IsRef<NodeAttrs::Use>, DFG);
RefMap &RUM = RealUseMap[PA.Id];
for (NodeAddr<UseNode*> UA : PUs) {
std::map<NodeId,RegisterAggr> &PUM = PhiUp[UA.Id];
RegisterRef UR = UA.Addr->getRegRef(DFG);
for (const std::pair<const NodeId, RegisterAggr> &P : PUM) {
bool Changed = false;
const RegisterAggr &MidDefs = P.second;
// Collect the set PropUp of uses that are reached by the current
// phi PA, and are not covered by any intervening def between the
// currently visited use UA and the upward phi P.
if (MidDefs.hasCoverOf(UR))
continue;
SubMap &SM = Subs[MidDefs];
// General algorithm:
// for each (R,U) : U is use node of R, U is reached by PA
// if MidDefs does not cover (R,U)
// then add (R-MidDefs,U) to RealUseMap[P]
//
for (const std::pair<const RegisterId, NodeRefSet> &T : RUM) {
RegisterRef R(T.first);
// The current phi (PA) could be a phi for a regmask. It could
// reach a whole variety of uses that are not related to the
// specific upward phi (P.first).
const RegisterAggr &DRs = PhiDRs.at(P.first);
if (!DRs.hasAliasOf(R))
continue;
R = PRI.mapTo(DRs.intersectWith(R), T.first);
for (std::pair<NodeId,LaneBitmask> V : T.second) {
LaneBitmask M = R.Mask & V.second;
if (M.none())
continue;
if (RegisterRef SS = ClearIn(RegisterRef(R.Reg, M), MidDefs, SM)) {
NodeRefSet &RS = RealUseMap[P.first][SS.Reg];
Changed |= RS.insert({V.first,SS.Mask}).second;
}
}
}
if (Changed)
PhiUQ.push_back(P.first);
}
}
}
if (Trace) {
dbgs() << "Real use map:\n";
for (auto I : RealUseMap) {
dbgs() << "phi " << Print<NodeId>(I.first, DFG);
NodeAddr<PhiNode*> PA = DFG.addr<PhiNode*>(I.first);
NodeList Ds = PA.Addr->members_if(DFG.IsRef<NodeAttrs::Def>, DFG);
if (!Ds.empty()) {
RegisterRef RR = NodeAddr<DefNode*>(Ds[0]).Addr->getRegRef(DFG);
dbgs() << '<' << Print<RegisterRef>(RR, DFG) << '>';
} else {
dbgs() << "<noreg>";
}
dbgs() << " -> " << Print<RefMap>(I.second, DFG) << '\n';
}
}
}
void Liveness::computeLiveIns() {
// Populate the node-to-block map. This speeds up the calculations
// significantly.
NBMap.clear();
for (NodeAddr<BlockNode*> BA : DFG.getFunc().Addr->members(DFG)) {
MachineBasicBlock *BB = BA.Addr->getCode();
for (NodeAddr<InstrNode*> IA : BA.Addr->members(DFG)) {
for (NodeAddr<RefNode*> RA : IA.Addr->members(DFG))
NBMap.insert(std::make_pair(RA.Id, BB));
NBMap.insert(std::make_pair(IA.Id, BB));
}
}
MachineFunction &MF = DFG.getMF();
// Compute IDF first, then the inverse.
decltype(IIDF) IDF;
for (MachineBasicBlock &B : MF) {
auto F1 = MDF.find(&B);
if (F1 == MDF.end())
continue;
SetVector<MachineBasicBlock*> IDFB(F1->second.begin(), F1->second.end());
for (unsigned i = 0; i < IDFB.size(); ++i) {
auto F2 = MDF.find(IDFB[i]);
if (F2 != MDF.end())
IDFB.insert(F2->second.begin(), F2->second.end());
}
// Add B to the IDF(B). This will put B in the IIDF(B).
IDFB.insert(&B);
IDF[&B].insert(IDFB.begin(), IDFB.end());
}
for (auto I : IDF)
for (auto S : I.second)
IIDF[S].insert(I.first);
computePhiInfo();
NodeAddr<FuncNode*> FA = DFG.getFunc();
NodeList Blocks = FA.Addr->members(DFG);
// Build the phi live-on-entry map.
for (NodeAddr<BlockNode*> BA : Blocks) {
MachineBasicBlock *MB = BA.Addr->getCode();
RefMap &LON = PhiLON[MB];
for (auto P : BA.Addr->members_if(DFG.IsCode<NodeAttrs::Phi>, DFG))
for (const RefMap::value_type &S : RealUseMap[P.Id])
LON[S.first].insert(S.second.begin(), S.second.end());
}
if (Trace) {
dbgs() << "Phi live-on-entry map:\n";
for (auto &I : PhiLON)
dbgs() << "block #" << I.first->getNumber() << " -> "
<< Print<RefMap>(I.second, DFG) << '\n';
}
// Build the phi live-on-exit map. Each phi node has some set of reached
// "real" uses. Propagate this set backwards into the block predecessors
// through the reaching defs of the corresponding phi uses.
for (NodeAddr<BlockNode*> BA : Blocks) {
NodeList Phis = BA.Addr->members_if(DFG.IsCode<NodeAttrs::Phi>, DFG);
for (NodeAddr<PhiNode*> PA : Phis) {
RefMap &RUs = RealUseMap[PA.Id];
if (RUs.empty())
continue;
NodeSet SeenUses;
for (auto U : PA.Addr->members_if(DFG.IsRef<NodeAttrs::Use>, DFG)) {
if (!SeenUses.insert(U.Id).second)
continue;
NodeAddr<PhiUseNode*> PUA = U;
if (PUA.Addr->getReachingDef() == 0)
continue;
// Each phi has some set (possibly empty) of reached "real" uses,
// that is, uses that are part of the compiled program. Such a use
// may be located in some farther block, but following a chain of
// reaching defs will eventually lead to this phi.
// Any chain of reaching defs may fork at a phi node, but there
// will be a path upwards that will lead to this phi. Now, this
// chain will need to fork at this phi, since some of the reached
// uses may have definitions joining in from multiple predecessors.
// For each reached "real" use, identify the set of reaching defs
// coming from each predecessor P, and add them to PhiLOX[P].
//
auto PrA = DFG.addr<BlockNode*>(PUA.Addr->getPredecessor());
RefMap &LOX = PhiLOX[PrA.Addr->getCode()];
for (const std::pair<const RegisterId, NodeRefSet> &RS : RUs) {
// We need to visit each individual use.
for (std::pair<NodeId,LaneBitmask> P : RS.second) {
// Create a register ref corresponding to the use, and find
// all reaching defs starting from the phi use, and treating
// all related shadows as a single use cluster.
RegisterRef S(RS.first, P.second);
NodeList Ds = getAllReachingDefs(S, PUA, true, false, NoRegs);
for (NodeAddr<DefNode*> D : Ds) {
// Calculate the mask corresponding to the visited def.
RegisterAggr TA(PRI);
TA.insert(D.Addr->getRegRef(DFG)).intersect(S);
LaneBitmask TM = TA.makeRegRef().Mask;
LOX[S.Reg].insert({D.Id, TM});
}
}
}
for (NodeAddr<PhiUseNode*> T : DFG.getRelatedRefs(PA, PUA))
SeenUses.insert(T.Id);
} // for U : phi uses
} // for P : Phis
} // for B : Blocks
if (Trace) {
dbgs() << "Phi live-on-exit map:\n";
for (auto &I : PhiLOX)
dbgs() << "block #" << I.first->getNumber() << " -> "
<< Print<RefMap>(I.second, DFG) << '\n';
}
RefMap LiveIn;
traverse(&MF.front(), LiveIn);
// Add function live-ins to the live-in set of the function entry block.
LiveMap[&MF.front()].insert(DFG.getLiveIns());
if (Trace) {
// Dump the liveness map
for (MachineBasicBlock &B : MF) {
std::vector<RegisterRef> LV;
for (const MachineBasicBlock::RegisterMaskPair &LI : B.liveins())
LV.push_back(RegisterRef(LI.PhysReg, LI.LaneMask));
llvm::sort(LV);
dbgs() << printMBBReference(B) << "\t rec = {";
for (auto I : LV)
dbgs() << ' ' << Print<RegisterRef>(I, DFG);
dbgs() << " }\n";
//dbgs() << "\tcomp = " << Print<RegisterAggr>(LiveMap[&B], DFG) << '\n';
LV.clear();
const RegisterAggr &LG = LiveMap[&B];
for (auto I = LG.rr_begin(), E = LG.rr_end(); I != E; ++I)
LV.push_back(*I);
llvm::sort(LV);
dbgs() << "\tcomp = {";
for (auto I : LV)
dbgs() << ' ' << Print<RegisterRef>(I, DFG);
dbgs() << " }\n";
}
}
}
void Liveness::resetLiveIns() {
for (auto &B : DFG.getMF()) {
// Remove all live-ins.
std::vector<unsigned> T;
for (const MachineBasicBlock::RegisterMaskPair &LI : B.liveins())
T.push_back(LI.PhysReg);
for (auto I : T)
B.removeLiveIn(I);
// Add the newly computed live-ins.
const RegisterAggr &LiveIns = LiveMap[&B];
for (const RegisterRef R : make_range(LiveIns.rr_begin(), LiveIns.rr_end()))
B.addLiveIn({MCPhysReg(R.Reg), R.Mask});
}
}
void Liveness::resetKills() {
for (auto &B : DFG.getMF())
resetKills(&B);
}
void Liveness::resetKills(MachineBasicBlock *B) {
auto CopyLiveIns = [this] (MachineBasicBlock *B, BitVector &LV) -> void {
for (auto I : B->liveins()) {
MCSubRegIndexIterator S(I.PhysReg, &TRI);
if (!S.isValid()) {
LV.set(I.PhysReg);
continue;
}
do {
LaneBitmask M = TRI.getSubRegIndexLaneMask(S.getSubRegIndex());
if ((M & I.LaneMask).any())
LV.set(S.getSubReg());
++S;
} while (S.isValid());
}
};
BitVector LiveIn(TRI.getNumRegs()), Live(TRI.getNumRegs());
CopyLiveIns(B, LiveIn);
for (auto SI : B->successors())
CopyLiveIns(SI, Live);
for (MachineInstr &MI : llvm::reverse(*B)) {
if (MI.isDebugInstr())
continue;
MI.clearKillInfo();
for (auto &Op : MI.operands()) {
// An implicit def of a super-register may not necessarily start a
// live range of it, since an implicit use could be used to keep parts
// of it live. Instead of analyzing the implicit operands, ignore
// implicit defs.
if (!Op.isReg() || !Op.isDef() || Op.isImplicit())
continue;
Register R = Op.getReg();
if (!Register::isPhysicalRegister(R))
continue;
for (MCSubRegIterator SR(R, &TRI, true); SR.isValid(); ++SR)
Live.reset(*SR);
}
for (auto &Op : MI.operands()) {
if (!Op.isReg() || !Op.isUse() || Op.isUndef())
continue;
Register R = Op.getReg();
if (!Register::isPhysicalRegister(R))
continue;
bool IsLive = false;
for (MCRegAliasIterator AR(R, &TRI, true); AR.isValid(); ++AR) {
if (!Live[*AR])
continue;
IsLive = true;
break;
}
if (!IsLive)
Op.setIsKill(true);
for (MCSubRegIterator SR(R, &TRI, true); SR.isValid(); ++SR)
Live.set(*SR);
}
}
}
// Helper function to obtain the basic block containing the reaching def
// of the given use.
MachineBasicBlock *Liveness::getBlockWithRef(NodeId RN) const {
auto F = NBMap.find(RN);
if (F != NBMap.end())
return F->second;
llvm_unreachable("Node id not in map");
}
void Liveness::traverse(MachineBasicBlock *B, RefMap &LiveIn) {
// The LiveIn map, for each (physical) register, contains the set of live
// reaching defs of that register that are live on entry to the associated
// block.
// The summary of the traversal algorithm:
//
// R is live-in in B, if there exists a U(R), such that rdef(R) dom B
// and (U \in IDF(B) or B dom U).
//
// for (C : children) {
// LU = {}
// traverse(C, LU)
// LiveUses += LU
// }
//
// LiveUses -= Defs(B);
// LiveUses += UpwardExposedUses(B);
// for (C : IIDF[B])
// for (U : LiveUses)
// if (Rdef(U) dom C)
// C.addLiveIn(U)
//
// Go up the dominator tree (depth-first).
MachineDomTreeNode *N = MDT.getNode(B);
for (auto I : *N) {
RefMap L;
MachineBasicBlock *SB = I->getBlock();
traverse(SB, L);
for (auto S : L)
LiveIn[S.first].insert(S.second.begin(), S.second.end());
}
if (Trace) {
dbgs() << "\n-- " << printMBBReference(*B) << ": " << __func__
<< " after recursion into: {";
for (auto I : *N)
dbgs() << ' ' << I->getBlock()->getNumber();
dbgs() << " }\n";
dbgs() << " LiveIn: " << Print<RefMap>(LiveIn, DFG) << '\n';
dbgs() << " Local: " << Print<RegisterAggr>(LiveMap[B], DFG) << '\n';
}
// Add reaching defs of phi uses that are live on exit from this block.
RefMap &PUs = PhiLOX[B];
for (auto &S : PUs)
LiveIn[S.first].insert(S.second.begin(), S.second.end());
if (Trace) {
dbgs() << "after LOX\n";
dbgs() << " LiveIn: " << Print<RefMap>(LiveIn, DFG) << '\n';
dbgs() << " Local: " << Print<RegisterAggr>(LiveMap[B], DFG) << '\n';
}
// The LiveIn map at this point has all defs that are live-on-exit from B,
// as if they were live-on-entry to B. First, we need to filter out all
// defs that are present in this block. Then we will add reaching defs of
// all upward-exposed uses.
// To filter out the defs, first make a copy of LiveIn, and then re-populate
// LiveIn with the defs that should remain.
RefMap LiveInCopy = LiveIn;
LiveIn.clear();
for (const std::pair<const RegisterId, NodeRefSet> &LE : LiveInCopy) {
RegisterRef LRef(LE.first);
NodeRefSet &NewDefs = LiveIn[LRef.Reg]; // To be filled.
const NodeRefSet &OldDefs = LE.second;
for (NodeRef OR : OldDefs) {
// R is a def node that was live-on-exit
auto DA = DFG.addr<DefNode*>(OR.first);
NodeAddr<InstrNode*> IA = DA.Addr->getOwner(DFG);
NodeAddr<BlockNode*> BA = IA.Addr->getOwner(DFG);
if (B != BA.Addr->getCode()) {
// Defs from a different block need to be preserved. Defs from this
// block will need to be processed further, except for phi defs, the
// liveness of which is handled through the PhiLON/PhiLOX maps.
NewDefs.insert(OR);
continue;
}
// Defs from this block need to stop the liveness from being
// propagated upwards. This only applies to non-preserving defs,
// and to the parts of the register actually covered by those defs.
// (Note that phi defs should always be preserving.)
RegisterAggr RRs(PRI);
LRef.Mask = OR.second;
if (!DFG.IsPreservingDef(DA)) {
assert(!(IA.Addr->getFlags() & NodeAttrs::Phi));
// DA is a non-phi def that is live-on-exit from this block, and
// that is also located in this block. LRef is a register ref
// whose use this def reaches. If DA covers LRef, then no part
// of LRef is exposed upwards.A
if (RRs.insert(DA.Addr->getRegRef(DFG)).hasCoverOf(LRef))
continue;
}
// DA itself was not sufficient to cover LRef. In general, it is
// the last in a chain of aliased defs before the exit from this block.
// There could be other defs in this block that are a part of that
// chain. Check that now: accumulate the registers from these defs,
// and if they all together cover LRef, it is not live-on-entry.
for (NodeAddr<DefNode*> TA : getAllReachingDefs(DA)) {
// DefNode -> InstrNode -> BlockNode.
NodeAddr<InstrNode*> ITA = TA.Addr->getOwner(DFG);
NodeAddr<BlockNode*> BTA = ITA.Addr->getOwner(DFG);
// Reaching defs are ordered in the upward direction.
if (BTA.Addr->getCode() != B) {
// We have reached past the beginning of B, and the accumulated
// registers are not covering LRef. The first def from the
// upward chain will be live.
// Subtract all accumulated defs (RRs) from LRef.
RegisterRef T = RRs.clearIn(LRef);
assert(T);
NewDefs.insert({TA.Id,T.Mask});
break;
}
// TA is in B. Only add this def to the accumulated cover if it is
// not preserving.
if (!(TA.Addr->getFlags() & NodeAttrs::Preserving))
RRs.insert(TA.Addr->getRegRef(DFG));
// If this is enough to cover LRef, then stop.
if (RRs.hasCoverOf(LRef))
break;
}
}
}
emptify(LiveIn);
if (Trace) {
dbgs() << "after defs in block\n";
dbgs() << " LiveIn: " << Print<RefMap>(LiveIn, DFG) << '\n';
dbgs() << " Local: " << Print<RegisterAggr>(LiveMap[B], DFG) << '\n';
}
// Scan the block for upward-exposed uses and add them to the tracking set.
for (auto I : DFG.getFunc().Addr->findBlock(B, DFG).Addr->members(DFG)) {
NodeAddr<InstrNode*> IA = I;
if (IA.Addr->getKind() != NodeAttrs::Stmt)
continue;
for (NodeAddr<UseNode*> UA : IA.Addr->members_if(DFG.IsUse, DFG)) {
if (UA.Addr->getFlags() & NodeAttrs::Undef)
continue;
RegisterRef RR = UA.Addr->getRegRef(DFG);
for (NodeAddr<DefNode*> D : getAllReachingDefs(UA))
if (getBlockWithRef(D.Id) != B)
LiveIn[RR.Reg].insert({D.Id,RR.Mask});
}
}
if (Trace) {
dbgs() << "after uses in block\n";
dbgs() << " LiveIn: " << Print<RefMap>(LiveIn, DFG) << '\n';
dbgs() << " Local: " << Print<RegisterAggr>(LiveMap[B], DFG) << '\n';
}
// Phi uses should not be propagated up the dominator tree, since they
// are not dominated by their corresponding reaching defs.
RegisterAggr &Local = LiveMap[B];
RefMap &LON = PhiLON[B];
for (auto &R : LON) {
LaneBitmask M;
for (auto P : R.second)
M |= P.second;
Local.insert(RegisterRef(R.first,M));
}
if (Trace) {
dbgs() << "after phi uses in block\n";
dbgs() << " LiveIn: " << Print<RefMap>(LiveIn, DFG) << '\n';
dbgs() << " Local: " << Print<RegisterAggr>(Local, DFG) << '\n';
}
for (auto C : IIDF[B]) {
RegisterAggr &LiveC = LiveMap[C];
for (const std::pair<const RegisterId, NodeRefSet> &S : LiveIn)
for (auto R : S.second)
if (MDT.properlyDominates(getBlockWithRef(R.first), C))
LiveC.insert(RegisterRef(S.first, R.second));
}
}
void Liveness::emptify(RefMap &M) {
for (auto I = M.begin(), E = M.end(); I != E; )
I = I->second.empty() ? M.erase(I) : std::next(I);
}
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