[LV] Use createIterationCountCheck during epilogue skeleton creation.

Use helper already used for minimum trip count checks for the regular
ILV skeleton creation also for epilogue skeleton creation.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7535,25 +7535,12 @@ BasicBlock *
 EpilogueVectorizerMainLoop::emitIterationCountCheck(BasicBlock *Bypass,
                                                     bool ForEpilogue) {
   assert(Bypass && "Expected valid bypass basic block.");
-  ElementCount VFactor = ForEpilogue ? EPI.EpilogueVF : VF;
-  unsigned UFactor = ForEpilogue ? EPI.EpilogueUF : UF;
   Value *Count = getTripCount();
-  // Reuse existing vector loop preheader for TC checks.
-  // Note that new preheader block is generated for vector loop.
-  BasicBlock *const TCCheckBlock = LoopVectorPreHeader;
-  IRBuilder<> Builder(TCCheckBlock->getTerminator());
-
-  // Generate code to check if the loop's trip count is less than VF * UF of the
-  // main vector loop.
-  auto P = Cost->requiresScalarEpilogue(ForEpilogue ? EPI.EpilogueVF.isVector()
-                                                    : VF.isVector())
-               ? ICmpInst::ICMP_ULE
-               : ICmpInst::ICMP_ULT;
-
-  Value *CheckMinIters = Builder.CreateICmp(
-      P, Count, createStepForVF(Builder, Count->getType(), VFactor, UFactor),
-      "min.iters.check");
+  MinProfitableTripCount = ElementCount::getFixed(0);
+  Value *CheckMinIters = createIterationCountCheck(
+      ForEpilogue ? EPI.EpilogueVF : VF, ForEpilogue ? EPI.EpilogueUF : UF);
 
+  BasicBlock *const TCCheckBlock = LoopVectorPreHeader;
   if (!ForEpilogue)
     TCCheckBlock->setName("vector.main.loop.iter.check");
 

llvm/test/Transforms/LoopVectorize/AArch64/partial-reduce-dot-product-epilogue.ll

@@ -10,8 +10,7 @@ define i32 @dotp(ptr %a, ptr %b) #0 {
 ; CHECK-NEXT:  iter.check:
 ; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.vscale.i64()
 ; CHECK-NEXT:    [[TMP1:%.*]] = mul i64 [[TMP0]], 4
-; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 1024, [[TMP1]]
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[VEC_EPILOG_SCALAR_PH:%.*]], label [[VECTOR_MAIN_LOOP_ITER_CHECK:%.*]]
+; CHECK-NEXT:    br i1 false, label [[VEC_EPILOG_SCALAR_PH:%.*]], label [[VECTOR_MAIN_LOOP_ITER_CHECK:%.*]]
 ; CHECK:       vector.main.loop.iter.check:
 ; CHECK-NEXT:    br i1 false, label [[VEC_EPILOG_PH:%.*]], label [[VECTOR_PH:%.*]]
 ; CHECK:       vector.ph:

llvm/test/Transforms/LoopVectorize/AArch64/vector-loop-backedge-elimination-epilogue.ll

@@ -11,8 +11,7 @@ define void @test_remove_vector_loop_region_epilogue(ptr %dst, i1 %c)  {
 ; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TC]], 8
 ; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label %[[VEC_EPILOG_SCALAR_PH:.*]], label %[[VECTOR_MAIN_LOOP_ITER_CHECK:.*]]
 ; CHECK:       [[VECTOR_MAIN_LOOP_ITER_CHECK]]:
-; CHECK-NEXT:    [[MIN_ITERS_CHECK1:%.*]] = icmp ult i64 [[TC]], 64
-; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK1]], label %[[VEC_EPILOG_PH:.*]], label %[[VECTOR_PH:.*]]
+; CHECK-NEXT:    br i1 true, label %[[VEC_EPILOG_PH:.*]], label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
 ; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[TC]], 64
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[TC]], [[N_MOD_VF]]