[RDA] getInstFromId: find instructions. NFC.

[SjoerdMeijer]

Summary

To find the instruction in the block for a given ID, first a count and then a lookup was performed in the map, which is almost the same thing, thus doing double the work.

[samparker]

This doesn't look safe to me. lookup will return a default constructed value if an existing object doesn't exist and I'm pretty sure this will be 0. This is also a perfectly reasonable number for InstId to be, therefore providing the wrong MI when an instruction has been inserted as the first instruction in the block, without RDA knowing about it.

[SjoerdMeijer]

Ah, yes, thanks for catching. We can just use find instead.

[SjoerdMeijer]

got rid of the lambda for readability.

[samparker]

Ok.

llvm/lib/CodeGen/ReachingDefAnalysis.cpp

222

Could just return MI here without going through F.

[SjoerdMeijer]

llvm/lib/CodeGen/ReachingDefAnalysis.cpp

222

yep, cheers, will change that before committing.

llvm/include/llvm/CodeGen/ReachingDefAnalysis.h

private:
   /// doesn't care whether or not we consider a register killed.
   using OutRegsInfoMap = SmallVector<LiveRegsDefInfo, 4>;
   OutRegsInfoMap MBBOutRegsInfos;
 
   /// Current instruction number.
   /// The first instruction in each basic block is 0.
   int CurInstr;
 
-  /// Maps instructions to their instruction Ids, relative to the begining of
+  /// Maps instructions to their instruction Ids, relative to the beginning of
   /// their basic blocks.
   DenseMap<MachineInstr *, int> InstIds;
 
   /// All reaching defs of a given RegUnit for a given MBB.
   using MBBRegUnitDefs = SmallVector<int, 1>;
   /// All reaching defs of all reg units for a given MBB
   using MBBDefsInfo = std::vector<MBBRegUnitDefs>;
   /// All reaching defs of all reg units for a all MBBs

llvm/lib/CodeGen/ReachingDefAnalysis.cpp

assert(static_cast<size_t>(MBB->getNumber()) < MBBReachingDefs.size() &&
          "Unexpected basic block number.");
   assert(InstId < static_cast<int>(MBB->size()) &&
          "Unexpected instruction id.");
 
   if (InstId < 0)
     return nullptr;
 
   for (auto &MI : *MBB) {
-    if (InstIds.count(&MI) && InstIds.lookup(&MI) == InstId)
+    auto F = InstIds.find(&MI);
+    if (F != InstIds.end() && F->second == InstId)
       return &MI;
   }
+
   return nullptr;
 }
 
 int
 ReachingDefAnalysis::getClearance(MachineInstr *MI, MCPhysReg PhysReg) const {
   assert(InstIds.count(MI) && "Unexpected machine instuction.");
   return InstIds.lookup(MI) - getReachingDef(MI, PhysReg);
 }