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authorEvan Cheng <evan.cheng@apple.com>2010-08-17 01:20:36 +0000
committerEvan Cheng <evan.cheng@apple.com>2010-08-17 01:20:36 +0000
commit97b9b97853d7e4fbb5c8460ef28126013c76e9a9 (patch)
tree00177661907fa80d2ee615063908e042e57911b9 /lib
parent922157c83440e0197e7fd962cf7030491a8069b1 (diff)
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PHI elimination should not break back edge. It can cause some significant code placement issues. rdar://8263994
good: LBB0_2: mov r2, r0 . . . mov r1, r2 bne LBB0_2 bad: LBB0_2: mov r2, r0 . . . @ BB#3: mov r1, r2 b LBB0_2 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111221 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r--lib/CodeGen/MachineBasicBlock.cpp11
-rw-r--r--lib/CodeGen/PHIElimination.cpp8
2 files changed, 14 insertions, 5 deletions
diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index a27ee47943..895653d18d 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/lib/CodeGen/MachineBasicBlock.cpp
@@ -439,6 +439,14 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
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();
MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
DEBUG(dbgs() << "PHIElimination splitting critical edge:"
@@ -471,8 +479,7 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
P->getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, this);
- if (MachineLoopInfo *MLI =
- P->getAnalysisIfAvailable<MachineLoopInfo>())
+ if (MLI)
if (MachineLoop *TIL = MLI->getLoopFor(this)) {
// 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.
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index 7bf0aa23af..105f20b448 100644
--- a/lib/CodeGen/PHIElimination.cpp
+++ b/lib/CodeGen/PHIElimination.cpp
@@ -20,6 +20,7 @@
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Function.h"
@@ -44,9 +45,9 @@ char &llvm::PHIEliminationID = PHIElimination::ID;
void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreserved<LiveVariables>();
+ AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineDominatorTree>();
- // rdar://7401784 This would be nice:
- // AU.addPreservedID(MachineLoopInfoID);
+ AU.addPreservedID(MachineLoopInfoID);
MachineFunctionPass::getAnalysisUsage(AU);
}
@@ -382,6 +383,7 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
if (MBB.empty() || !MBB.front().isPHI() || MBB.isLandingPad())
return false; // Quick exit for basic blocks without PHIs.
+ bool Changed = false;
for (MachineBasicBlock::const_iterator BBI = MBB.begin(), BBE = MBB.end();
BBI != BBE && BBI->isPHI(); ++BBI) {
for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2) {
@@ -391,7 +393,7 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
// (not considering PHI nodes). If the register is live in to this block
// anyway, we would gain nothing from splitting.
if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB))
- PreMBB->SplitCriticalEdge(&MBB, this);
+ Changed |= PreMBB->SplitCriticalEdge(&MBB, this) != 0;
}
}
return true;