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[ShrinkWrap] Add a target hook to check whether or not 

the target can handle a given basic block as prologue
or epilogue.

Related to <rdar://problem/20821487>

llvm-svn: 238292
This commit is contained in:
Quentin Colombet 2015-05-27 06:25:48 +00:00
parent 3e0dcc27d5
commit 8083588a7e
2 changed files with 34 additions and 5 deletions
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24
llvm/include/llvm/Target/TargetFrameLowering.h
View File

@ -257,6 +257,30 @@ public:
llvm_unreachable("Call Frame Pseudo Instructions do not exist on this "
"target!");
}
/// Check whether or not the given \p MBB can be used as a prologue
/// for the target.
/// The prologue will be inserted first in this basic block.
/// This method is used by the shrink-wrapping pass to decide if
/// \p MBB will be correctly handled by the target.
/// As soon as the target enable shrink-wrapping without overriding
/// this method, we assume that each basic block is a valid
/// prologue.
virtual bool canUseAsPrologue(const MachineBasicBlock &MBB) const {
return true;
}
/// Check whether or not the given \p MBB can be used as a epilogue
/// for the target.
/// The epilogue will be inserted before the first terminator of that block.
/// This method is used by the shrink-wrapping pass to decide if
/// \p MBB will be correctly handled by the target.
/// As soon as the target enable shrink-wrapping without overriding
/// this method, we assume that each basic block is a valid
/// epilogue.
virtual bool canUseAsEpilogue(const MachineBasicBlock &MBB) const {
return true;
}
};
} // End llvm namespace

15
llvm/lib/CodeGen/ShrinkWrap.cpp
View File

@ -62,6 +62,8 @@
// 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.
@ -338,6 +340,7 @@ bool ShrinkWrap::runOnMachineFunction(MachineFunction &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() << ' '
@ -345,13 +348,15 @@ bool ShrinkWrap::runOnMachineFunction(MachineFunction &MF) {
<< 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;