// To know about callee-saved.
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/Support/Debug.h"
+// To query the target about frame lowering.
+#include "llvm/Target/TargetFrameLowering.h"
// To know about frame setup operation.
#include "llvm/Target/TargetInstrInfo.h"
// To access TargetInstrInfo.
STATISTIC(NumCandidatesDropped,
"Number of shrink-wrapping candidates dropped because of frequency");
+static cl::opt<cl::boolOrDefault>
+ EnableShrinkWrapOpt("enable-shrink-wrap", cl::Hidden,
+ cl::desc("enable the shrink-wrapping pass"));
+
namespace {
/// \brief Class to determine where the safe point to insert the
/// prologue and epilogue are.
/// shrink-wrapping.
bool ArePointsInteresting() const { return Save != Entry && Save && Restore; }
+ /// \brief Check if shrink wrapping is enabled for this target and function.
+ static bool isShrinkWrapEnabled(const MachineFunction &MF);
+
public:
static char ID;
// Fix (C).
if (Save && Restore && Save != Restore &&
MLI->getLoopFor(Save) != MLI->getLoopFor(Restore)) {
- if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore))
- // Push Save outside of this loop.
- Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
- else
+ 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.
+ MachineBasicBlock *IDom = FindIDom<>(*Save, Save->predecessors(), *MDT);
+ if (IDom != Save)
+ Save = IDom;
+ else {
+ Save = nullptr;
+ break;
+ }
+ }
+ else {
+ // If the loop does not exit, there is no point in looking
+ // for a post-dominator outside the loop.
+ SmallVector<MachineBasicBlock*, 4> ExitBlocks;
+ MLI->getLoopFor(Restore)->getExitingBlocks(ExitBlocks);
// Push Restore outside of this loop.
- Restore = FindIDom<>(*Restore, Restore->successors(), *MPDT);
+ // Look for the immediate post-dominator of the loop exits.
+ MachineBasicBlock *IPdom = Restore;
+ for (MachineBasicBlock *LoopExitBB: ExitBlocks) {
+ IPdom = FindIDom<>(*IPdom, LoopExitBB->successors(), *MPDT);
+ if (!IPdom)
+ break;
+ }
+ // If the immediate post-dominator is not in a less nested loop,
+ // 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;
+ else {
+ Restore = nullptr;
+ break;
+ }
+ }
}
}
}
bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
- if (MF.empty())
+ if (MF.empty() || !isShrinkWrapEnabled(MF))
return false;
+
DEBUG(dbgs() << "**** Analysing " << MF.getName() << '\n');
init(MF);
DEBUG(dbgs() << "\n ** Results **\nFrequency of the Entry: " << EntryFreq
<< '\n');
+ const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
do {
DEBUG(dbgs() << "Shrink wrap candidates (#, Name, Freq):\nSave: "
<< Save->getNumber() << ' ' << Save->getName() << ' '
<< Restore->getNumber() << ' ' << Restore->getName() << ' '
<< MBFI->getBlockFreq(Restore).getFrequency() << '\n');
- bool IsSaveCheap;
- if ((IsSaveCheap = EntryFreq >= MBFI->getBlockFreq(Save).getFrequency()) &&
- EntryFreq >= MBFI->getBlockFreq(Restore).getFrequency())
+ bool IsSaveCheap, TargetCanUseSaveAsPrologue = false;
+ if (((IsSaveCheap = EntryFreq >= MBFI->getBlockFreq(Save).getFrequency()) &&
+ EntryFreq >= MBFI->getBlockFreq(Restore).getFrequency()) &&
+ ((TargetCanUseSaveAsPrologue = TFI->canUseAsPrologue(*Save)) &&
+ TFI->canUseAsEpilogue(*Restore)))
break;
- DEBUG(dbgs() << "New points are too expensive\n");
+ DEBUG(dbgs() << "New points are too expensive or invalid for the target\n");
MachineBasicBlock *NewBB;
- if (!IsSaveCheap) {
+ if (!IsSaveCheap || !TargetCanUseSaveAsPrologue) {
Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
if (!Save)
break;
++NumCandidates;
return false;
}
+
+bool ShrinkWrap::isShrinkWrapEnabled(const MachineFunction &MF) {
+ const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
+
+ switch (EnableShrinkWrapOpt) {
+ case cl::BOU_UNSET:
+ return TFI->enableShrinkWrapping(MF);
+ // If EnableShrinkWrap is set, it takes precedence on whatever the
+ // target sets. The rational is that we assume we want to test
+ // something related to shrink-wrapping.
+ case cl::BOU_TRUE:
+ return true;
+ case cl::BOU_FALSE:
+ return false;
+ }
+ llvm_unreachable("Invalid shrink-wrapping state");
+}