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
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index 7bf0aa2..105f20b 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 @@
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 @@
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 @@
// (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;