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Move the decision logic whether it's a good idea to split a critical edge to clients. Also fixed an erroneous check. An edge is only a back edge when the from and to blocks are in the same loop.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111256 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-08-17 17:43:50 +00:00
parent fc8042a122
commit e008384508
3 changed files with 15 additions and 13 deletions
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10
lib/CodeGen/MachineBasicBlock.cpp
View File

@ -439,14 +439,6 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
if (TII->AnalyzeBranch(*this, TBB, FBB, Cond)) if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
return NULL; return NULL;
// Avoid splitting backedges of loops. It would introduce small out-of-line
// blocks into the loop which is very bad for code placement.
if (this == Succ)
return NULL;
MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>();
if (MLI->isLoopHeader(Succ))
return NULL;
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock(); MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB); MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
DEBUG(dbgs() << "Splitting critical edge:" DEBUG(dbgs() << "Splitting critical edge:"
@ -479,7 +471,7 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
P->getAnalysisIfAvailable<MachineDominatorTree>()) P->getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, this); MDT->addNewBlock(NMBB, this);
if (MLI) if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
if (MachineLoop *TIL = MLI->getLoopFor(this)) { if (MachineLoop *TIL = MLI->getLoopFor(this)) {
// If one or the other blocks were not in a loop, the new block is not // If one or the other blocks were not in a loop, the new block is not
// either, and thus LI doesn't need to be updated. // either, and thus LI doesn't need to be updated.

9
lib/CodeGen/PHIElimination.cpp
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@ -53,6 +53,7 @@ void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &MF) { bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &MF) {
MRI = &MF.getRegInfo(); MRI = &MF.getRegInfo();
MLI = getAnalysisIfAvailable<MachineLoopInfo>();
bool Changed = false; bool Changed = false;
@ -392,9 +393,15 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
// We break edges when registers are live out from the predecessor block // We break edges when registers are live out from the predecessor block
// (not considering PHI nodes). If the register is live in to this block // (not considering PHI nodes). If the register is live in to this block
// anyway, we would gain nothing from splitting. // anyway, we would gain nothing from splitting.
if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) // Avoid splitting backedges of loops. It would introduce small
// out-of-line blocks into the loop which is very bad for code placement.
if (PreMBB != &MBB &&
!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) {
if (!(MLI->getLoopFor(PreMBB) == MLI->getLoopFor(&MBB) &&
MLI->isLoopHeader(&MBB)))
Changed |= PreMBB->SplitCriticalEdge(&MBB, this) != 0; Changed |= PreMBB->SplitCriticalEdge(&MBB, this) != 0;
} }
} }
}
return true; return true;
} }

5
lib/CodeGen/PHIElimination.h
View File

@ -13,15 +13,18 @@
#include "llvm/ADT/DenseMap.h" #include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h" #include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h" #include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
namespace llvm { namespace llvm {
class LiveVariables; class LiveVariables;
class MachineRegisterInfo;
class MachineLoopInfo;
/// Lower PHI instructions to copies. /// Lower PHI instructions to copies.
class PHIElimination : public MachineFunctionPass { class PHIElimination : public MachineFunctionPass {
MachineRegisterInfo *MRI; // Machine register information MachineRegisterInfo *MRI; // Machine register information
MachineLoopInfo *MLI;
public: public:
static char ID; // Pass identification, replacement for typeid static char ID; // Pass identification, replacement for typeid