#include "llvm/CodeGen/Passes.h"
// To know about callee-saved.
#include "llvm/CodeGen/RegisterClassInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Support/Debug.h"
// To query the target about frame lowering.
/// \brief Check if \p MI uses or defines a callee-saved register or
/// a frame index. If this is the case, this means \p MI must happen
/// after Save and before Restore.
- bool useOrDefCSROrFI(const MachineInstr &MI) const;
+ bool useOrDefCSROrFI(const MachineInstr &MI, RegScavenger *RS) const;
- const SetOfRegs &getCurrentCSRs() const {
+ const SetOfRegs &getCurrentCSRs(RegScavenger *RS) const {
if (CurrentCSRs.empty()) {
BitVector SavedRegs;
const TargetFrameLowering *TFI =
MachineFunc->getSubtarget().getFrameLowering();
- TFI->determineCalleeSaves(*MachineFunc, SavedRegs, nullptr);
+ TFI->determineCalleeSaves(*MachineFunc, SavedRegs, RS);
for (int Reg = SavedRegs.find_first(); Reg != -1;
Reg = SavedRegs.find_next(Reg))
/// and Save and Restore still match the safe point definition.
/// Such point may not exist and Save and/or Restore may be null after
/// this call.
- void updateSaveRestorePoints(MachineBasicBlock &MBB);
+ void updateSaveRestorePoints(MachineBasicBlock &MBB, RegScavenger *RS);
/// \brief Initialize the pass for \p MF.
void init(MachineFunction &MF) {
/// \brief Check if shrink wrapping is enabled for this target and function.
static bool isShrinkWrapEnabled(const MachineFunction &MF);
-
+
public:
static char ID;
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(ShrinkWrap, "shrink-wrap", "Shrink Wrap Pass", false, false)
-bool ShrinkWrap::useOrDefCSROrFI(const MachineInstr &MI) const {
+bool ShrinkWrap::useOrDefCSROrFI(const MachineInstr &MI,
+ RegScavenger *RS) const {
if (MI.getOpcode() == FrameSetupOpcode ||
MI.getOpcode() == FrameDestroyOpcode) {
DEBUG(dbgs() << "Frame instruction: " << MI << '\n');
UseOrDefCSR = RCI.getLastCalleeSavedAlias(PhysReg);
} else if (MO.isRegMask()) {
// Check if this regmask clobbers any of the CSRs.
- for (unsigned Reg : getCurrentCSRs()) {
+ for (unsigned Reg : getCurrentCSRs(RS)) {
if (MO.clobbersPhysReg(Reg)) {
UseOrDefCSR = true;
break;
return IDom;
}
-void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB) {
+void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
+ RegScavenger *RS) {
// Get rid of the easy cases first.
if (!Save)
Save = &MBB;
// terminator.
if (Restore == &MBB) {
for (const MachineInstr &Terminator : MBB.terminators()) {
- if (!useOrDefCSROrFI(Terminator))
+ if (!useOrDefCSROrFI(Terminator, RS))
continue;
// One of the terminator needs to happen before the restore point.
if (MBB.succ_empty()) {
while (Save && Restore &&
(!(SaveDominatesRestore = MDT->dominates(Save, Restore)) ||
!(RestorePostDominatesSave = MPDT->dominates(Restore, Save)) ||
- MLI->getLoopFor(Save) != MLI->getLoopFor(Restore))) {
+ // Post-dominance is not enough in loops to ensure that all uses/defs
+ // are after the prologue and before the epilogue at runtime.
+ // E.g.,
+ // while(1) {
+ // Save
+ // Restore
+ // if (...)
+ // break;
+ // use/def CSRs
+ // }
+ // All the uses/defs of CSRs are dominated by Save and post-dominated
+ // by Restore. However, the CSRs uses are still reachable after
+ // Restore and before Save are executed.
+ //
+ // For now, just push the restore/save points outside of loops.
+ // FIXME: Refine the criteria to still find interesting cases
+ // for loops.
+ MLI->getLoopFor(Save) || MLI->getLoopFor(Restore))) {
// Fix (A).
if (!SaveDominatesRestore) {
Save = MDT->findNearestCommonDominator(Save, Restore);
Restore = MPDT->findNearestCommonDominator(Restore, Save);
// Fix (C).
- if (Save && Restore && Save != Restore &&
- MLI->getLoopFor(Save) != MLI->getLoopFor(Restore)) {
+ if (Save && Restore &&
+ (MLI->getLoopFor(Save) || MLI->getLoopFor(Restore))) {
if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
// Push Save outside of this loop if immediate dominator is different
- // from save block. If immediate dominator is not different, bail out.
+ // from save block. If immediate dominator is not different, bail out.
MachineBasicBlock *IDom = FindIDom<>(*Save, Save->predecessors(), *MDT);
if (IDom != Save)
Save = IDom;
Save = nullptr;
break;
}
- }
- else {
+ } else {
// If the loop does not exit, there is no point in looking
// for a post-dominator outside the loop.
SmallVector<MachineBasicBlock*, 4> ExitBlocks;
// then we are stuck in a program with an infinite loop.
// In that case, we will not find a safe point, hence, bail out.
if (IPdom && MLI->getLoopDepth(IPdom) < MLI->getLoopDepth(Restore))
- Restore = IPdom;
+ Restore = IPdom;
else {
Restore = nullptr;
break;
}
- }
+ }
}
}
}
init(MF);
+ const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
+ std::unique_ptr<RegScavenger> RS(
+ TRI->requiresRegisterScavenging(MF) ? new RegScavenger() : nullptr);
+
for (MachineBasicBlock &MBB : MF) {
DEBUG(dbgs() << "Look into: " << MBB.getNumber() << ' ' << MBB.getName()
<< '\n');
}
for (const MachineInstr &MI : MBB) {
- if (!useOrDefCSROrFI(MI))
+ if (!useOrDefCSROrFI(MI, RS.get()))
continue;
// Save (resp. restore) point must dominate (resp. post dominate)
// MI. Look for the proper basic block for those.
- updateSaveRestorePoints(MBB);
+ updateSaveRestorePoints(MBB, RS.get());
// If we are at a point where we cannot improve the placement of
// save/restore instructions, just give up.
if (!ArePointsInteresting()) {
break;
NewBB = Restore;
}
- updateSaveRestorePoints(*NewBB);
+ updateSaveRestorePoints(*NewBB, RS.get());
} while (Save && Restore);
if (!ArePointsInteresting()) {
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