[PATCH] D94981: [LiveDebugVariables] Add cache for SkipPHIsLabelsAndDebug to prevent iterating the same set of PHI/LABEL/Debug instructions repeatedly.

[David Blaikie via Phabricator via llvm-commits]

dblaikie added inline comments.


================
Comment at: llvm/lib/CodeGen/LiveDebugVariables.cpp:1309-1315
+      if (MachineInstr *BI = BBSkipInstsMap[MBB])
+        BeginIt = std::next(MachineBasicBlock::iterator(BI));
+      else
+        BeginIt = MBB->begin();
+      MachineBasicBlock::iterator I = MBB->SkipPHIsLabelsAndDebug(BeginIt);
+      if (I != MBB->begin())
+        BBSkipInstsMap[MBB] = &*std::prev(I);
----------------
Could you store iterators in the map instead of pointers? Would save having to do the `&*` dance on the way in and the `MachineBasicBlock::iterator` dance on the way out?
Also, it'd be good to avoid the extra BBSkipInstsMap lookup, if possible. Would this work?
```
auto& I = BBSkipInstsMap.insert(MBB, MBB->begin()).first->second;
I = MBB->SkipPHIsLabelsAndDebug(I);
return I;
```


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D94981/new/

https://reviews.llvm.org/D94981