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misched: handle scheduler that insert instructions at empty region boundaries. 

And add comments, since this is obviously confusing.

llvm-svn: 152445
This commit is contained in:
Andrew Trick 2012-03-09 22:34:56 +00:00
parent 2a70e65436
commit af1bee7235
1 changed files with 12 additions and 3 deletions
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15
llvm/lib/CodeGen/MachineScheduler.cpp
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@ -144,10 +144,18 @@ bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
Scheduler->startBlock(MBB); Scheduler->startBlock(MBB);
// Break the block into scheduling regions [I, RegionEnd), and schedule each // Break the block into scheduling regions [I, RegionEnd), and schedule each
// region as soon as it is discovered. // region as soon as it is discovered. RegionEnd points the the scheduling
// boundary at the bottom of the region. The DAG does not include RegionEnd,
// but the region does (i.e. the next RegionEnd is above the previous
// RegionBegin). If the current block has no terminator then RegionEnd ==
// MBB->end() for the bottom region.
//
// The Scheduler may insert instructions during either schedule() or
// exitRegion(), even for empty regions. So the local iterators 'I' and
// 'RegionEnd' are invalid across these calls.
unsigned RemainingCount = MBB->size(); unsigned RemainingCount = MBB->size();
for(MachineBasicBlock::iterator RegionEnd = MBB->end(); for(MachineBasicBlock::iterator RegionEnd = MBB->end();
RegionEnd != MBB->begin();) { RegionEnd != MBB->begin(); RegionEnd = Scheduler->begin()) {
// Avoid decrementing RegionEnd for blocks with no terminator. // Avoid decrementing RegionEnd for blocks with no terminator.
if (RegionEnd != MBB->end() if (RegionEnd != MBB->end()
|| TII->isSchedulingBoundary(llvm::prior(RegionEnd), MBB, *MF)) { || TII->isSchedulingBoundary(llvm::prior(RegionEnd), MBB, *MF)) {
@ -170,8 +178,8 @@ bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
// Skip empty scheduling regions (0 or 1 schedulable instructions). // Skip empty scheduling regions (0 or 1 schedulable instructions).
if (I == RegionEnd || I == llvm::prior(RegionEnd)) { if (I == RegionEnd || I == llvm::prior(RegionEnd)) {
// Close the current region. Bundle the terminator if needed. // Close the current region. Bundle the terminator if needed.
// This invalidates 'RegionEnd' and 'I'.
Scheduler->exitRegion(); Scheduler->exitRegion();
RegionEnd = I;
continue; continue;
} }
DEBUG(dbgs() << "MachineScheduling " << MF->getFunction()->getName() DEBUG(dbgs() << "MachineScheduling " << MF->getFunction()->getName()
@ -181,6 +189,7 @@ bool MachineScheduler::runOnMachineFunction(MachineFunction &mf) {
dbgs() << " Remaining: " << RemainingCount << "\n"); dbgs() << " Remaining: " << RemainingCount << "\n");
// Schedule a region: possibly reorder instructions. // Schedule a region: possibly reorder instructions.
// This invalidates 'RegionEnd' and 'I'.
Scheduler->schedule(); Scheduler->schedule();
// Close the current region. // Close the current region.