[InstCombine] Don't use getFirstNonPHI in FoldIntegerTypedPHI

[thegameg]

Summary

getFirstNonPHI iterates over all the instructions in a block until it finds a non-PHI.

Then, the loop starts from the beginning of the block and goes through all the instructions until it reaches the instruction found by getFirstNonPHI.

Instead of doing that, just stop when a non-PHI is found.

This reduces the compile-time of a test case discussed in https://reviews.llvm.org/D47023 by 13x.

Not entirely sure how to come up with a test case for this since it's a compile time issue that would significantly slow down running the tests.

[fhahn]

llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

183

Could you just use the iterator range BB->phis()? This should automatically iterate until it hits a non-phi instruction.

[thegameg]

llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

183

For some reason using phis() gives me similar results as before when using getFirstNonPHI. I'll look into it.

[fhahn]

LGTM

llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

183

Ah right, no worries then!

llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

Instruction *InstCombiner::FoldIntegerTypedPHI(PHINode &PN) {
   }
 
   // Now search for a matching PHI
   auto *BB = PN.getParent();
   assert(AvailablePtrVals.size() == PN.getNumIncomingValues() &&
          "Not enough available ptr typed incoming values");
   PHINode *MatchingPtrPHI = nullptr;
   unsigned NumPhis = 0;
-  for (auto II = BB->begin(), EI = BasicBlock::iterator(BB->getFirstNonPHI());
-       II != EI; II++, NumPhis++) {
+  for (auto II = BB->begin(); II != BB->end(); II++, NumPhis++) {
     // FIXME: consider handling this in AggressiveInstCombine
+    PHINode *PtrPHI = dyn_cast<PHINode>(II);
+    if (!PtrPHI)
+      break;
     if (NumPhis > MaxNumPhis)
       return nullptr;
-    PHINode *PtrPHI = dyn_cast<PHINode>(II);
-    if (!PtrPHI || PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType())
+    if (PtrPHI == &PN || PtrPHI->getType() != IntToPtr->getType())
       continue;
     MatchingPtrPHI = PtrPHI;
     for (unsigned i = 0; i != PtrPHI->getNumIncomingValues(); ++i) {
       if (AvailablePtrVals[i] !=
           PtrPHI->getIncomingValueForBlock(PN.getIncomingBlock(i))) {
         MatchingPtrPHI = nullptr;
         break;
       }