// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
+//
+// This pass performs optimization of sign / zero extension instructions. It
+// may be extended to handle other instructions of similar property.
+//
+// On some targets, some instructions, e.g. X86 sign / zero extension, may
+// leave the source value in the lower part of the result. This pass will
+// replace (some) uses of the pre-extension value with uses of the sub-register
+// of the results.
+//
+//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ext-opt"
#include "llvm/CodeGen/Passes.h"
public:
static char ID; // Pass identification
- OptimizeExts() : MachineFunctionPass(&ID) {}
+ OptimizeExts() : MachineFunctionPass(ID) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
- AU.addRequired<MachineDominatorTree>();
- AU.addPreserved<MachineDominatorTree>();
+ if (Aggressive) {
+ AU.addRequired<MachineDominatorTree>();
+ AU.addPreserved<MachineDominatorTree>();
+ }
}
+
+ private:
+ bool OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
+ SmallPtrSet<MachineInstr*, 8> &LocalMIs);
};
}
char OptimizeExts::ID = 0;
-static RegisterPass<OptimizeExts>
-X("opt-exts", "Optimize sign / zero extensions");
+INITIALIZE_PASS(OptimizeExts, "opt-exts",
+ "Optimize sign / zero extensions", false, false);
FunctionPass *llvm::createOptimizeExtsPass() { return new OptimizeExts(); }
+/// OptimizeInstr - If instruction is a copy-like instruction, i.e. it reads
+/// a single register and writes a single register and it does not modify
+/// the source, and if the source value is preserved as a sub-register of
+/// the result, then replace all reachable uses of the source with the subreg
+/// of the result.
+/// Do not generate an EXTRACT that is used only in a debug use, as this
+/// changes the code. Since this code does not currently share EXTRACTs, just
+/// ignore all debug uses.
+bool OptimizeExts::OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
+ SmallPtrSet<MachineInstr*, 8> &LocalMIs) {
+ LocalMIs.insert(MI);
+
+ unsigned SrcReg, DstReg, SubIdx;
+ if (!TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx))
+ return false;
+
+ if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
+ TargetRegisterInfo::isPhysicalRegister(SrcReg))
+ return false;
+
+ MachineRegisterInfo::use_nodbg_iterator UI = MRI->use_nodbg_begin(SrcReg);
+ if (++UI == MRI->use_nodbg_end())
+ // No other uses.
+ return false;
+
+ // Ok, 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;
+ UI = MRI->use_nodbg_begin(DstReg);
+ for (MachineRegisterInfo::use_nodbg_iterator UE = MRI->use_nodbg_end();
+ UI != UE; ++UI)
+ ReachedBBs.insert(UI->getParent());
+
+ bool ExtendLife = true;
+ // Uses that are in the same BB of uses of the result of the instruction.
+ SmallVector<MachineOperand*, 8> Uses;
+ // Uses that the result of the instruction can reach.
+ SmallVector<MachineOperand*, 8> ExtendedUses;
+
+ UI = MRI->use_nodbg_begin(SrcReg);
+ for (MachineRegisterInfo::use_nodbg_iterator UE = MRI->use_nodbg_end();
+ UI != UE; ++UI) {
+ MachineOperand &UseMO = UI.getOperand();
+ MachineInstr *UseMI = &*UI;
+ if (UseMI == MI)
+ continue;
+ if (UseMI->isPHI()) {
+ ExtendLife = false;
+ continue;
+ }
+
+ // It's an error to translate this:
+ //
+ // %reg1025 = <sext> %reg1024
+ // ...
+ // %reg1026 = SUBREG_TO_REG 0, %reg1024, 4
+ //
+ // into this:
+ //
+ // %reg1025 = <sext> %reg1024
+ // ...
+ // %reg1027 = COPY %reg1025:4
+ // %reg1026 = SUBREG_TO_REG 0, %reg1027, 4
+ //
+ // The problem here is that SUBREG_TO_REG is there to assert that an
+ // implicit zext occurs. It doesn't insert a zext instruction. If we allow
+ // the COPY here, it will give us the value after the <sext>, not the
+ // original value of %reg1024 before <sext>.
+ if (UseMI->getOpcode() == TargetOpcode::SUBREG_TO_REG)
+ continue;
+
+ MachineBasicBlock *UseMBB = UseMI->getParent();
+ if (UseMBB == MBB) {
+ // Local uses that come after the extension.
+ if (!LocalMIs.count(UseMI))
+ Uses.push_back(&UseMO);
+ } else if (ReachedBBs.count(UseMBB))
+ // Non-local uses where the result of extension is used. Always replace
+ // these unless it's a PHI.
+ Uses.push_back(&UseMO);
+ else if (Aggressive && DT->dominates(MBB, UseMBB))
+ // We may want to extend live range of the extension result in order to
+ // replace these uses.
+ ExtendedUses.push_back(&UseMO);
+ else {
+ // Both will be live out of the def MBB anyway. Don't extend live range of
+ // the extension result.
+ ExtendLife = false;
+ break;
+ }
+ }
+
+ if (ExtendLife && !ExtendedUses.empty())
+ // Ok, we'll extend the liveness of the extension result.
+ std::copy(ExtendedUses.begin(), ExtendedUses.end(),
+ std::back_inserter(Uses));
+
+ // Now replace all uses.
+ bool Changed = false;
+ if (!Uses.empty()) {
+ SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
+ // Look for PHI uses of the extended result, we don't want to extend the
+ // liveness of a PHI input. It breaks all kinds of assumptions down
+ // stream. A PHI use is expected to be the kill of its source values.
+ UI = MRI->use_nodbg_begin(DstReg);
+ for (MachineRegisterInfo::use_nodbg_iterator UE = MRI->use_nodbg_end();
+ UI != UE; ++UI)
+ if (UI->isPHI())
+ PHIBBs.insert(UI->getParent());
+
+ const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
+ for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
+ MachineOperand *UseMO = Uses[i];
+ MachineInstr *UseMI = UseMO->getParent();
+ MachineBasicBlock *UseMBB = UseMI->getParent();
+ if (PHIBBs.count(UseMBB))
+ continue;
+ unsigned NewVR = MRI->createVirtualRegister(RC);
+ BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
+ TII->get(TargetOpcode::COPY), NewVR)
+ .addReg(DstReg, 0, SubIdx);
+ UseMO->setReg(NewVR);
+ ++NumReuse;
+ Changed = true;
+ }
+ }
+
+ return Changed;
+}
+
bool OptimizeExts::runOnMachineFunction(MachineFunction &MF) {
TM = &MF.getTarget();
TII = TM->getInstrInfo();
MRI = &MF.getRegInfo();
- DT = &getAnalysis<MachineDominatorTree>();
+ DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : 0;
bool Changed = false;
SmallPtrSet<MachineInstr*, 8> LocalMIs;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = &*I;
+ LocalMIs.clear();
for (MachineBasicBlock::iterator MII = I->begin(), ME = I->end(); MII != ME;
++MII) {
MachineInstr *MI = &*MII;
- LocalMIs.insert(MI);
-
- unsigned SrcReg, DstReg, SubIdx;
- if (TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx)) {
- if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
- TargetRegisterInfo::isPhysicalRegister(SrcReg))
- continue;
-
- MachineRegisterInfo::use_iterator UI = MRI->use_begin(SrcReg);
- if (++UI == MRI->use_end())
- // No other uses.
- continue;
-
- // Ok, 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;
- UI = MRI->use_begin(DstReg);
- for (MachineRegisterInfo::use_iterator UE = MRI->use_end(); UI != UE;
- ++UI)
- ReachedBBs.insert(UI->getParent());
-
- bool ExtendLife = true;
- SmallVector<MachineOperand*, 8> Uses;
- SmallVector<MachineOperand*, 8> ExtendedUses;
-
- UI = MRI->use_begin(SrcReg);
- for (MachineRegisterInfo::use_iterator UE = MRI->use_end(); UI != UE;
- ++UI) {
- MachineOperand &UseMO = UI.getOperand();
- MachineInstr *UseMI = &*UI;
- if (UseMI == MI)
- continue;
- MachineBasicBlock *UseMBB = UseMI->getParent();
- if (UseMBB == MBB) {
- // Local uses that come after the extension.
- if (!LocalMIs.count(UseMI))
- Uses.push_back(&UseMO);
- } else if (ReachedBBs.count(UseMBB))
- // Non-local uses where the result of extension is used. Always
- // replace these.
- Uses.push_back(&UseMO);
- else if (Aggressive && DT->dominates(MBB, UseMBB))
- // We may want to extend live range of the extension result in order
- // to replace these uses.
- ExtendedUses.push_back(&UseMO);
- else {
- // Both will be live out of the def MBB anyway. Don't extend live
- // range of the extension result.
- ExtendLife = false;
- break;
- }
- }
-
- if (ExtendLife && !ExtendedUses.empty())
- // Ok, we'll extend the liveness of the extension result.
- std::copy(ExtendedUses.begin(), ExtendedUses.end(),
- std::back_inserter(Uses));
-
- // Now replace all uses.
- if (!Uses.empty()) {
- const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
- for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
- MachineOperand *UseMO = Uses[i];
- MachineInstr *UseMI = UseMO->getParent();
- MachineBasicBlock *UseMBB = UseMI->getParent();
- unsigned NewVR = MRI->createVirtualRegister(RC);
- BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
- TII->get(TargetInstrInfo::EXTRACT_SUBREG), NewVR)
- .addReg(DstReg).addImm(SubIdx);
- UseMO->setReg(NewVR);
- ++NumReuse;
- Changed = true;
- }
- }
- }
+ Changed |= OptimizeInstr(MI, MBB, LocalMIs);
}
}
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