// v1 = bitcast v0
// = v0
//
+// - Optimize Loads:
+//
+// Loads that can be folded into a later instruction. A load is foldable
+// if it loads to virtual registers and the virtual register defined has
+// a single use.
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "peephole-opt"
#include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
-#include "llvm/Support/CommandLine.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/Statistic.h"
using namespace llvm;
// Optimize Extensions
STATISTIC(NumBitcasts, "Number of bitcasts eliminated");
STATISTIC(NumCmps, "Number of compares eliminated");
STATISTIC(NumImmFold, "Number of move immediate folded");
+STATISTIC(NumLoadFold, "Number of loads folded");
+STATISTIC(NumSelects, "Number of selects optimized");
namespace {
class PeepholeOptimizer : public MachineFunctionPass {
bool optimizeCmpInstr(MachineInstr *MI, MachineBasicBlock *MBB);
bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
SmallPtrSet<MachineInstr*, 8> &LocalMIs);
+ bool optimizeSelect(MachineInstr *MI);
bool isMoveImmediate(MachineInstr *MI,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
bool foldImmediate(MachineInstr *MI, MachineBasicBlock *MBB,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs);
+ bool isLoadFoldable(MachineInstr *MI, unsigned &FoldAsLoadDefReg);
};
}
if (!DstRC)
return false;
+ // The ext instr may be operating on a sub-register of SrcReg as well.
+ // PPC::EXTSW is a 32 -> 64-bit sign extension, but it reads a 64-bit
+ // register.
+ // If UseSrcSubIdx is Set, SubIdx also applies to SrcReg, and only uses of
+ // SrcReg:SubIdx should be replaced.
+ bool UseSrcSubIdx = TM->getRegisterInfo()->
+ getSubClassWithSubReg(MRI->getRegClass(SrcReg), SubIdx) != 0;
+
// The source has other uses. See if we can replace the other uses with use of
// the result of the extension.
SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
continue;
}
+ // Only accept uses of SrcReg:SubIdx.
+ if (UseSrcSubIdx && UseMO.getSubReg() != SubIdx)
+ continue;
+
// It's an error to translate this:
//
// %reg1025 = <sext> %reg1024
}
unsigned NewVR = MRI->createVirtualRegister(RC);
- BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
- TII->get(TargetOpcode::COPY), NewVR)
+ MachineInstr *Copy = BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
+ TII->get(TargetOpcode::COPY), NewVR)
.addReg(DstReg, 0, SubIdx);
-
+ // SubIdx applies to both SrcReg and DstReg when UseSrcSubIdx is set.
+ if (UseSrcSubIdx) {
+ Copy->getOperand(0).setSubReg(SubIdx);
+ Copy->getOperand(0).setIsUndef();
+ }
UseMO->setReg(NewVR);
++NumReuse;
Changed = true;
MachineBasicBlock *MBB) {
// If this instruction is a comparison against zero and isn't comparing a
// physical register, we can try to optimize it.
- unsigned SrcReg;
+ unsigned SrcReg, SrcReg2;
int CmpMask, CmpValue;
- if (!TII->AnalyzeCompare(MI, SrcReg, CmpMask, CmpValue) ||
- TargetRegisterInfo::isPhysicalRegister(SrcReg))
+ if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue) ||
+ TargetRegisterInfo::isPhysicalRegister(SrcReg) ||
+ (SrcReg2 != 0 && TargetRegisterInfo::isPhysicalRegister(SrcReg2)))
return false;
// Attempt to optimize the comparison instruction.
- if (TII->OptimizeCompareInstr(MI, SrcReg, CmpMask, CmpValue, MRI)) {
+ if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
++NumCmps;
return true;
}
return false;
}
+/// Optimize a select instruction.
+bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) {
+ unsigned TrueOp = 0;
+ unsigned FalseOp = 0;
+ bool Optimizable = false;
+ SmallVector<MachineOperand, 4> Cond;
+ if (TII->analyzeSelect(MI, Cond, TrueOp, FalseOp, Optimizable))
+ return false;
+ if (!Optimizable)
+ return false;
+ if (!TII->optimizeSelect(MI))
+ return false;
+ MI->eraseFromParent();
+ ++NumSelects;
+ return true;
+}
+
+/// isLoadFoldable - Check whether MI is a candidate for folding into a later
+/// instruction. We only fold loads to virtual registers and the virtual
+/// register defined has a single use.
+bool PeepholeOptimizer::isLoadFoldable(MachineInstr *MI,
+ unsigned &FoldAsLoadDefReg) {
+ if (!MI->canFoldAsLoad() || !MI->mayLoad())
+ return false;
+ const MCInstrDesc &MCID = MI->getDesc();
+ if (MCID.getNumDefs() != 1)
+ return false;
+
+ unsigned Reg = MI->getOperand(0).getReg();
+ // To reduce compilation time, we check MRI->hasOneUse when inserting
+ // loads. It should be checked when processing uses of the load, since
+ // uses can be removed during peephole.
+ if (!MI->getOperand(0).getSubReg() &&
+ TargetRegisterInfo::isVirtualRegister(Reg) &&
+ MRI->hasOneUse(Reg)) {
+ FoldAsLoadDefReg = Reg;
+ return true;
+ }
+ return false;
+}
+
bool PeepholeOptimizer::isMoveImmediate(MachineInstr *MI,
SmallSet<unsigned, 4> &ImmDefRegs,
DenseMap<unsigned, MachineInstr*> &ImmDefMIs) {
}
bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
+ DEBUG(dbgs() << "********** PEEPHOLE OPTIMIZER **********\n");
+ DEBUG(dbgs() << "********** Function: " << MF.getName() << '\n');
+
if (DisablePeephole)
return false;
SmallPtrSet<MachineInstr*, 8> LocalMIs;
SmallSet<unsigned, 4> ImmDefRegs;
DenseMap<unsigned, MachineInstr*> ImmDefMIs;
+ unsigned FoldAsLoadDefReg;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = &*I;
LocalMIs.clear();
ImmDefRegs.clear();
ImmDefMIs.clear();
+ FoldAsLoadDefReg = 0;
- bool First = true;
- MachineBasicBlock::iterator PMII;
for (MachineBasicBlock::iterator
MII = I->begin(), MIE = I->end(); MII != MIE; ) {
MachineInstr *MI = &*MII;
+ // We may be erasing MI below, increment MII now.
+ ++MII;
LocalMIs.insert(MI);
+ // If there exists an instruction which belongs to the following
+ // categories, we will discard the load candidate.
if (MI->isLabel() || MI->isPHI() || MI->isImplicitDef() ||
MI->isKill() || MI->isInlineAsm() || MI->isDebugValue() ||
MI->hasUnmodeledSideEffects()) {
- ++MII;
+ FoldAsLoadDefReg = 0;
continue;
}
-
- if (MI->isBitcast()) {
- if (optimizeBitcastInstr(MI, MBB)) {
- // MI is deleted.
- LocalMIs.erase(MI);
- Changed = true;
- MII = First ? I->begin() : llvm::next(PMII);
- continue;
- }
- } else if (MI->isCompare()) {
- if (optimizeCmpInstr(MI, MBB)) {
- // MI is deleted.
- LocalMIs.erase(MI);
- Changed = true;
- MII = First ? I->begin() : llvm::next(PMII);
- continue;
- }
+ if (MI->mayStore() || MI->isCall())
+ FoldAsLoadDefReg = 0;
+
+ if ((MI->isBitcast() && optimizeBitcastInstr(MI, MBB)) ||
+ (MI->isCompare() && optimizeCmpInstr(MI, MBB)) ||
+ (MI->isSelect() && optimizeSelect(MI))) {
+ // MI is deleted.
+ LocalMIs.erase(MI);
+ Changed = true;
+ continue;
}
if (isMoveImmediate(MI, ImmDefRegs, ImmDefMIs)) {
SeenMoveImm = true;
} else {
Changed |= optimizeExtInstr(MI, MBB, LocalMIs);
+ // optimizeExtInstr might have created new instructions after MI
+ // and before the already incremented MII. Adjust MII so that the
+ // next iteration sees the new instructions.
+ MII = MI;
+ ++MII;
if (SeenMoveImm)
Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
}
- First = false;
- PMII = MII;
- ++MII;
+ // Check whether MI is a load candidate for folding into a later
+ // instruction. If MI is not a candidate, check whether we can fold an
+ // earlier load into MI.
+ if (!isLoadFoldable(MI, FoldAsLoadDefReg) && FoldAsLoadDefReg) {
+ // We need to fold load after optimizeCmpInstr, since optimizeCmpInstr
+ // can enable folding by converting SUB to CMP.
+ MachineInstr *DefMI = 0;
+ MachineInstr *FoldMI = TII->optimizeLoadInstr(MI, MRI,
+ FoldAsLoadDefReg, DefMI);
+ if (FoldMI) {
+ // Update LocalMIs since we replaced MI with FoldMI and deleted DefMI.
+ DEBUG(dbgs() << "Replacing: " << *MI);
+ DEBUG(dbgs() << " With: " << *FoldMI);
+ LocalMIs.erase(MI);
+ LocalMIs.erase(DefMI);
+ LocalMIs.insert(FoldMI);
+ MI->eraseFromParent();
+ DefMI->eraseFromParent();
+ ++NumLoadFold;
+
+ // MI is replaced with FoldMI.
+ Changed = true;
+ continue;
+ }
+ }
}
}
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