lib/CodeGen/ShrinkWrap.cpp

12 // The safe point for the prologue (resp. epilogue) is called Save
16 // between 2) two executions of the Save (resp. Restore) point there is an
17 // execution of the Restore (resp. Save) point.
21 //   Save
25 // Indeed, the execution looks like Save -> Restore -> Save -> Restore ...
28 //   Save
35 // Indeed, the execution looks like Save -> Save -> ... -> Restore -> Restore.
55 // For property #1 for Save.
107   MachineBasicBlock *Save;
115   /// Hold the loop information. Used to determine if Save and Restore
134   /// after Save and before Restore.
152   /// \brief Update the Save and Restore points such that \p MBB is in
153   /// the region that is dominated by Save and post-dominated by Restore
154   /// and Save and Restore still match the safe point definition.
155   /// Such point may not exist and Save and/or Restore may be null after
164     Save = nullptr;
179   /// Check whether or not Save and Restore points are still interesting for
181   bool ArePointsInteresting() const { return Save != Entry && Save && Restore; }
275   if (!Save)
276     Save = &MBB;
278     Save = MDT->findNearestCommonDominator(Save, &MBB);
280   if (!Save) {
313   // Make sure Save and Restore are suitable for shrink-wrapping:
314   // 1. all path from Save needs to lead to Restore before exiting.
315   // 2. all path to Restore needs to go through Save from Entry.
317   // A. Save dominates Restore.
318   // B. Restore post-dominates Save.
319   // C. Save and Restore are in the same loop.
322   while (Save && Restore &&
323          (!(SaveDominatesRestore = MDT->dominates(Save, Restore)) ||
324           !(RestorePostDominatesSave = MPDT->dominates(Restore, Save)) ||
329           //  Save
335           // All the uses/defs of CSRs are dominated by Save and post-dominated
337           // Restore and before Save are executed.
342           MLI->getLoopFor(Save) || MLI->getLoopFor(Restore))) {
345       Save = MDT->findNearestCommonDominator(Save, Restore);
350       Restore = MPDT->findNearestCommonDominator(Restore, Save);
353     if (Save && Restore &&
354         (MLI->getLoopFor(Save) || MLI->getLoopFor(Restore))) {
355       if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
356         // Push Save outside of this loop if immediate dominator is different
358         Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
359         if (!Save)
458       // Save (resp. restore) point must dominate (resp. post dominate)
476     assert(!Save && !Restore && "We miss a shrink-wrap opportunity?!");
487                  << Save->getNumber() << ' ' << Save->getName() << ' '
488                  << MBFI->getBlockFreq(Save).getFrequency() << "\nRestore: "
493     if (((IsSaveCheap = EntryFreq >= MBFI->getBlockFreq(Save).getFrequency()) &&
495         ((TargetCanUseSaveAsPrologue = TFI->canUseAsPrologue(*Save)) &&
501       Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
502       if (!Save)
504       NewBB = Save;
513   } while (Save && Restore);
520   DEBUG(dbgs() << "Final shrink wrap candidates:\nSave: " << Save->getNumber()
521                << ' ' << Save->getName() << "\nRestore: "
525   MFI->setSavePoint(Save);