From 97b9b97853d7e4fbb5c8460ef28126013c76e9a9 Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Tue, 17 Aug 2010 01:20:36 +0000 Subject: 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 --- lib/CodeGen/PHIElimination.cpp | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'lib/CodeGen/PHIElimination.cpp') 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(); + AU.addRequired(); AU.addPreserved(); - // 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; -- cgit v1.2.3