[llvm] [VPlan] Check FOR/FMinMaxNum epilogue restrictions in VPlan. (PR #191815)

[via llvm-commits]

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@@ -24,21 +27,42 @@ define void @dead_for(ptr %a, i64 %N) {
 ; CHECK:       [[MIDDLE_BLOCK]]:
 ; CHECK-NEXT:    [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <8 x i64> [[WIDE_LOAD]], i32 7
 ; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
-; CHECK-NEXT:    br i1 [[CMP_N]], label %[[EXIT:.*]], label %[[VEC_EPILOG_PH]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label %[[EXIT:.*]], label %[[VEC_EPILOG_ITER_CHECK:.*]]
+; CHECK:       [[VEC_EPILOG_ITER_CHECK]]:
+; CHECK-NEXT:    [[MIN_EPILOG_ITERS_CHECK:%.*]] = icmp ult i64 [[N_MOD_VF]], 4
+; CHECK-NEXT:    br i1 [[MIN_EPILOG_ITERS_CHECK]], label %[[VEC_EPILOG_SCALAR_PH]], label %[[VEC_EPILOG_PH]], !prof [[PROF3:![0-9]+]]
 ; CHECK:       [[VEC_EPILOG_PH]]:
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ayalz wrote:

Previously, having a VEC_EPILOG_PH block w/o a vector epilog loop is somewhat confusing.

https://github.com/llvm/llvm-project/pull/191815