diff options
| -rw-r--r-- | lib/CodeGen/LiveIntervalAnalysis.cpp | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp index f8713cc1da..72b8bacb0a 100644 --- a/lib/CodeGen/LiveIntervalAnalysis.cpp +++ b/lib/CodeGen/LiveIntervalAnalysis.cpp @@ -41,6 +41,8 @@ STATISTIC(numIntervalsAfter, "Number of intervals after coalescing"); STATISTIC(numJoins , "Number of interval joins performed"); STATISTIC(numPeep , "Number of identity moves eliminated after coalescing"); STATISTIC(numFolded , "Number of loads/stores folded into instructions"); +STATISTIC(numAborts , "Number of times interval joining aborted"); +static cl::opt<bool> ReduceJoinPhys("reduce-joining-phy-regs", cl::Hidden); namespace { RegisterPass<LiveIntervals> X("liveintervals", "Live Interval Analysis"); @@ -931,6 +933,58 @@ bool LiveIntervals::JoinCopy(MachineInstr *CopyMI, isShorten = true; } + // We need to be careful about coalescing a source physical register with a + // virtual register. Once the coalescing is done, it cannot be broken and + // these are not spillable! If the destination interval uses are far away, + // think twice about coalescing them! + if (ReduceJoinPhys && !isDead && + MRegisterInfo::isPhysicalRegister(repSrcReg)) { + // Small function. No need to worry! + if (r2iMap_.size() <= allocatableRegs_.size() * 2) + goto TryJoin; + + LiveVariables::VarInfo& dvi = lv_->getVarInfo(repDstReg); + // Is the value used in the current BB or any immediate successroe BB? + MachineBasicBlock *SrcBB = CopyMI->getParent(); + if (!dvi.UsedBlocks[SrcBB->getNumber()]) { + for (MachineBasicBlock::succ_iterator SI = SrcBB->succ_begin(), + SE = SrcBB->succ_end(); SI != SE; ++SI) { + MachineBasicBlock *SuccMBB = *SI; + if (dvi.UsedBlocks[SuccMBB->getNumber()]) + goto TryJoin; + } + } + + // Ok, no use in this BB and no use in immediate successor BB's. Be really + // careful now! + // It's only used in one BB, forget about it! + if (dvi.UsedBlocks.count() <= 1) { + ++numAborts; + return false; + } + + // Examine all the blocks where the value is used. If any is in the same + // loop, then it's ok. Or if the current BB is a preheader of any of the + // loop that uses this value, that's ok as well. + const LoopInfo &LI = getAnalysis<LoopInfo>(); + const Loop *L = LI.getLoopFor(SrcBB->getBasicBlock()); + int UseBBNum = dvi.UsedBlocks.find_first(); + while (UseBBNum != -1) { + MachineBasicBlock *UseBB = mf_->getBlockNumbered(UseBBNum); + const Loop *UL = LI.getLoopFor(UseBB->getBasicBlock()); + if ((UL && UL == L) || // A use in the same loop + (UL && L && // A use in a loop and this BB is the preheader + UL->getLoopPreheader() == SrcBB->getBasicBlock())) + goto TryJoin; + UseBBNum = dvi.UsedBlocks.find_next(UseBBNum); + } + + // Don't do it! + ++numAborts; + return false; + } + +TryJoin: // Okay, attempt to join these two intervals. On failure, this returns false. // Otherwise, if one of the intervals being joined is a physreg, this method // always canonicalizes DestInt to be it. The output "SrcInt" will not have |