[LV] Don't pass loop preheader to getOrCreateVectorTripCount (NFCI).

The vector trip count must already be created when fixupIVUsers is
called. Don't pass the vector preheader there and delay retrieving the
vector loop header. This ensures we are re-using the already computed
trip count. Computing the trip count from scratch would not be correct,
as the IR may not be in a valid state yet.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2933,9 +2933,6 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
     for (PHINode &PN : Exit->phis())
       PSE.getSE()->forgetLcssaPhiWithNewPredecessor(OrigLoop, &PN);
 
-  VPRegionBlock *VectorRegion = State.Plan->getVectorLoopRegion();
-  VPBasicBlock *LatchVPBB = VectorRegion->getExitingBasicBlock();
-  Loop *VectorLoop = LI->getLoopFor(State.CFG.VPBB2IRBB[LatchVPBB]);
   if (Cost->requiresScalarEpilogue(VF.isVector())) {
     // No edge from the middle block to the unique exit block has been inserted
     // and there is nothing to fix from vector loop; phis should have incoming
@@ -2951,7 +2948,7 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
     // Fix-up external users of the induction variables.
     for (const auto &Entry : Legal->getInductionVars())
       fixupIVUsers(Entry.first, Entry.second,
-                   getOrCreateVectorTripCount(VectorLoop->getLoopPreheader()),
+                   getOrCreateVectorTripCount(nullptr),
                    IVEndValues[Entry.first], LoopMiddleBlock, Plan, State);
   }
 
@@ -2962,8 +2959,12 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
   for (Instruction *PI : PredicatedInstructions)
     sinkScalarOperands(&*PI);
 
+  VPRegionBlock *VectorRegion = State.Plan->getVectorLoopRegion();
+  VPBasicBlock *HeaderVPBB = VectorRegion->getEntryBasicBlock();
+  BasicBlock *HeaderBB = State.CFG.VPBB2IRBB[HeaderVPBB];
+
   // Remove redundant induction instructions.
-  cse(VectorLoop->getHeader());
+  cse(HeaderBB);
 
   // Set/update profile weights for the vector and remainder loops as original
   // loop iterations are now distributed among them. Note that original loop
@@ -2978,8 +2979,9 @@ void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
   // For scalable vectorization we can't know at compile time how many iterations
   // of the loop are handled in one vector iteration, so instead assume a pessimistic
   // vscale of '1'.
-  setProfileInfoAfterUnrolling(LI->getLoopFor(LoopScalarBody), VectorLoop,
-                               LI->getLoopFor(LoopScalarBody),
+  Loop *ScalarLoop = LI->getLoopFor(LoopScalarBody);
+  Loop *VectorLoop = LI->getLoopFor(HeaderBB);
+  setProfileInfoAfterUnrolling(ScalarLoop, VectorLoop, ScalarLoop,
                                VF.getKnownMinValue() * UF);
 }