diff options
Diffstat (limited to 'llvm')
| -rw-r--r-- | llvm/lib/CodeGen/LiveIntervals.cpp | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/llvm/lib/CodeGen/LiveIntervals.cpp b/llvm/lib/CodeGen/LiveIntervals.cpp index 4f17e31f716..8c2558af787 100644 --- a/llvm/lib/CodeGen/LiveIntervals.cpp +++ b/llvm/lib/CodeGen/LiveIntervals.cpp @@ -286,9 +286,9 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb, DEBUG(std::cerr << "\t\tregister: "; printRegName(interval.reg)); LiveVariables::VarInfo& vi = lv_->getVarInfo(interval.reg); - // iterate over all of the blocks that the variable is completely - // live in, adding them to the live interval. obviously we only - // need to do this once. + // Iterate over all of the blocks that the variable is completely + // live in, adding [insrtIndex(begin), instrIndex(end)+4) to the + // live interval. Obviously we only need to do this once. if (interval.empty()) { for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) { if (vi.AliveBlocks[i]) { @@ -337,6 +337,8 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb, MachineBasicBlock::iterator mi, LiveInterval& interval) { + // A physical register cannot be live across basic block, so its + // lifetime must end somewhere in its defining basic block. DEBUG(std::cerr << "\t\tregister: "; printRegName(interval.reg)); typedef LiveVariables::killed_iterator KillIter; @@ -345,7 +347,9 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb, unsigned start = getDefIndex(baseIndex); unsigned end = start; - // a variable can be dead by the instruction defining it + // If it is not used after definition, it is considered dead at + // the instruction defining it. Hence its interval is: + // [defSlot(def), defSlot(def)+1) for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi); ki != ke; ++ki) { if (interval.reg == ki->second) { @@ -355,7 +359,9 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb, } } - // a variable can only be killed by subsequent instructions + // If it is not dead on definition, it must be killed by a + // subsequent instruction. Hence its interval is: + // [defSlot(def), useSlot(def)+1) do { ++mi; baseIndex += InstrSlots::NUM; |
