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[Hexagon] Limit virtual register reuse range in FI elimination

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This commit is contained in:
Krzysztof Parzyszek 2021-03-25 13:43:55 -05:00
parent c1ee58a328
commit 607936d033
1 changed files with 51 additions and 29 deletions
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80
lib/Target/Hexagon/HexagonRegisterInfo.cpp
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@ -17,6 +17,7 @@
#include "HexagonSubtarget.h"
#include "HexagonTargetMachine.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/LiveRegUnits.h"
@ -43,9 +44,14 @@
using namespace llvm;
static cl::opt<unsigned> FrameIndexSearchLimit(
"hexagon-frame-index-search-limit", cl::init(32), cl::Hidden,
cl::desc("Limit on instruction search in frame index elimination"));
static cl::opt<unsigned> FrameIndexSearchRange(
"hexagon-frame-index-search-range", cl::init(32), cl::Hidden,
cl::desc("Limit on instruction search range in frame index elimination"));
static cl::opt<unsigned> FrameIndexReuseLimit(
"hexagon-frame-index-reuse-limit", cl::init(~0), cl::Hidden,
cl::desc("Limit on the number of reused registers in frame index "
"elimination"));
HexagonRegisterInfo::HexagonRegisterInfo(unsigned HwMode)
: HexagonGenRegisterInfo(Hexagon::R31, 0/*DwarfFlavor*/, 0/*EHFlavor*/,
@ -197,6 +203,7 @@ BitVector HexagonRegisterInfo::getReservedRegs(const MachineFunction &MF)
void HexagonRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
int SPAdj, unsigned FIOp,
RegScavenger *RS) const {
static unsigned ReuseCount = 0;
//
// Hexagon_TODO: Do we need to enforce this for Hexagon?
assert(SPAdj == 0 && "Unexpected");
@ -274,35 +281,50 @@ void HexagonRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
// Search backwards in the block for "Reg = A2_addi BP, RealOffset".
// This will give us a chance to avoid creating a new register.
Register ReuseBP;
unsigned SearchCount = 0, SearchLimit = FrameIndexSearchLimit;
bool PassedCall = false;
LiveRegUnits Defs(*this), Uses(*this);
for (auto I = std::next(II.getReverse()), E = MB.rend(); I != E; ++I) {
if (SearchCount == SearchLimit)
if (ReuseCount < FrameIndexReuseLimit) {
unsigned SearchCount = 0, SearchRange = FrameIndexSearchRange;
SmallSet<Register,2> SeenVRegs;
bool PassedCall = false;
LiveRegUnits Defs(*this), Uses(*this);
for (auto I = std::next(II.getReverse()), E = MB.rend(); I != E; ++I) {
if (SearchCount == SearchRange)
break;
++SearchCount;
const MachineInstr &BI = *I;
LiveRegUnits::accumulateUsedDefed(BI, Defs, Uses, this);
PassedCall |= BI.isCall();
for (const MachineOperand &Op : BI.operands()) {
if (SeenVRegs.size() > 1)
break;
if (Op.isReg() && Op.getReg().isVirtual())
SeenVRegs.insert(Op.getReg());
}
if (BI.getOpcode() != Hexagon::A2_addi)
continue;
if (BI.getOperand(1).getReg() != BP)
continue;
const auto &Op2 = BI.getOperand(2);
if (!Op2.isImm() || Op2.getImm() != RealOffset)
continue;
Register R = BI.getOperand(0).getReg();
if (R.isPhysical()) {
if (Defs.available(R))
ReuseBP = R;
} else if (R.isVirtual()) {
// Extending a range of a virtual register can be dangerous,
// since the scavenger will need to find a physical register
// for it. Avoid extending the range past a function call,
// and avoid overlapping it with another virtual register.
if (!PassedCall && SeenVRegs.size() <= 1)
ReuseBP = R;
}
break;
++SearchCount;
const MachineInstr &BI = *I;
LiveRegUnits::accumulateUsedDefed(BI, Defs, Uses, this);
PassedCall |= BI.isCall();
if (BI.getOpcode() != Hexagon::A2_addi)
continue;
if (BI.getOperand(1).getReg() != BP)
continue;
const auto &Op2 = BI.getOperand(2);
if (!Op2.isImm() || Op2.getImm() != RealOffset)
continue;
Register R = BI.getOperand(0).getReg();
if (R.isPhysical()) {
if (Defs.available(R))
ReuseBP = R;
} else if (R.isVirtual()) {
if (!PassedCall)
ReuseBP = R;
}
break;
if (ReuseBP)
++ReuseCount;
}
auto &MRI = MF.getRegInfo();