[llvm] [LV][NFC] Add branch weight test showing incorrect behaviour (PR #144682)

[Florian Hahn via llvm-commits]

================
@@ -1,53 +1,81 @@
-; RUN: opt < %s -S -passes=loop-vectorize -force-vector-interleave=1 -force-vector-width=4  -enable-epilogue-vectorization -epilogue-vectorization-force-VF=4 | FileCheck %s
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --filter "br" --filter "^.*:" --version 5
+; RUN: opt < %s -S -passes=loop-vectorize -force-vector-interleave=1 -force-vector-width=4  -enable-epilogue-vectorization \
+; RUN:   -epilogue-vectorization-force-VF=4 | FileCheck %s --check-prefix=MAINVF4IC1_EPI4
+; RUN: opt < %s -S -passes=loop-vectorize -force-vector-interleave=2 -force-vector-width=4  -enable-epilogue-vectorization \
+; RUN:   -epilogue-vectorization-force-VF=4 | FileCheck %s --check-prefix=MAINVF4IC2_EPI4
 
-; CHECK-LABEL: @f0(
-;
-; CHECK: entry:
-; CHECK:   br i1 %cmp.entry, label %iter.check, label %exit, !prof [[PROF_F0_ENTRY:![0-9]+]]
-;
-; CHECK: iter.check:
-; CHECK:   br i1 %min.iters.check, label %vec.epilog.scalar.ph, label %vector.scevcheck, !prof [[PROF_F0_UNLIKELY:![0-9]+]]
-;
-; CHECK: vector.scevcheck:
-; CHECK:   br i1 %4, label %vec.epilog.scalar.ph, label %vector.main.loop.iter.check, !prof [[PROF_F0_UNLIKELY]]
-;
-; CHECK: vector.main.loop.iter.check:
-; CHECK:   br i1 %min.iters.check1, label %vec.epilog.ph, label %vector.ph, !prof [[PROF_F0_UNLIKELY]]
-;
-; CHECK: vector.ph:
-; CHECK:   br label %vector.body
-;
-; CHECK: vector.body:
-; CHECK:   br i1 {{.+}}, label %middle.block, label %vector.body, !prof [[PROF_F0_VECTOR_BODY:![0-9]+]]
-;
-; CHECK: middle.block:
-; CHECK:   br i1 %cmp.n, label %exit.loopexit, label %vec.epilog.iter.check, !prof [[PROF_F0_MIDDLE_BLOCKS:![0-9]+]]
-;
-; CHECK: vec.epilog.iter.check:
-; CHECK:   br i1 %min.epilog.iters.check, label %vec.epilog.scalar.ph, label %vec.epilog.ph, !prof [[PROF_F0_VEC_EPILOGUE_SKIP:![0-9]+]]
-;
-; CHECK: vec.epilog.ph:
-; CHECK:   br label %vec.epilog.vector.body
-;
-; CHECK: vec.epilog.vector.body:
-; CHECK:   br i1 {{.+}}, label %vec.epilog.middle.block, label %vec.epilog.vector.body, !prof [[PROF_F0_VEC_EPILOG_VECTOR_BODY:![0-9]+]]
-;
-; CHECK: vec.epilog.middle.block:
-; CHECK:   br i1 %cmp.n{{.+}}, label %exit.loopexit, label %vec.epilog.scalar.ph, !prof [[PROF_F0_MIDDLE_BLOCKS:![0-9]+]]
-;
-; CHECK: vec.epilog.scalar.ph:
-; CHECK:   br label %loop
-;
-; CHECK: loop:
-; CHECK:   br i1 %cmp.loop, label %loop, label %exit.loopexit, !prof [[PROF_F0_LOOP:![0-9]+]]
+; FIXME: For MAINVF4IC2_EPI4 the branch weights in the terminator of
+; the VEC_EPILOG_ITER_CHECK block should be [4,4] since we process 8
+; scalar iterations in the main loop, leaving the remaining count to
+; be in the range [0,7]. That gives a 4:4 chance of skipping the
+; vector epilogue. I believe the problem lies in
+; EpilogueVectorizerEpilogueLoop::emitMinimumVectorEpilogueIterCountCheck
+; where the main loop VF is set to the same value as the epilogue VF.
+define void @f0(i8 %n, i32 %len, ptr %p) !prof !0 {
+; MAINVF4IC1_EPI4-LABEL: define void @f0(
+; MAINVF4IC1_EPI4-SAME: i8 [[N:%.*]], i32 [[LEN:%.*]], ptr [[P:%.*]]) !prof [[PROF0:![0-9]+]] {
+; MAINVF4IC1_EPI4:  [[ENTRY:.*:]]
+; MAINVF4IC1_EPI4:    br i1 [[CMP_ENTRY:%.*]], label %[[ITER_CHECK:.*]], label %[[EXIT:.*]], !prof [[PROF1:![0-9]+]]
+; MAINVF4IC1_EPI4:  [[ITER_CHECK]]:
+; MAINVF4IC1_EPI4:    br i1 [[MIN_ITERS_CHECK:%.*]], label %[[VEC_EPILOG_SCALAR_PH:.*]], label %[[VECTOR_SCEVCHECK:.*]], !prof [[PROF2:![0-9]+]]
+; MAINVF4IC1_EPI4:  [[VECTOR_SCEVCHECK]]:
+; MAINVF4IC1_EPI4:    br i1 [[TMP4:%.*]], label %[[VEC_EPILOG_SCALAR_PH]], label %[[VECTOR_MAIN_LOOP_ITER_CHECK:.*]], !prof [[PROF2]]
+; MAINVF4IC1_EPI4:  [[VECTOR_MAIN_LOOP_ITER_CHECK]]:
+; MAINVF4IC1_EPI4:    br i1 [[MIN_ITERS_CHECK1:%.*]], label %[[VEC_EPILOG_PH:.*]], label %[[VECTOR_PH:.*]], !prof [[PROF2]]
+; MAINVF4IC1_EPI4:  [[VECTOR_PH]]:
+; MAINVF4IC1_EPI4:    br label %[[VECTOR_BODY:.*]]
+; MAINVF4IC1_EPI4:  [[VECTOR_BODY]]:
+; MAINVF4IC1_EPI4:    br i1 [[TMP8:%.*]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !prof [[PROF3:![0-9]+]], !llvm.loop [[LOOP4:![0-9]+]]
+; MAINVF4IC1_EPI4:  [[MIDDLE_BLOCK]]:
+; MAINVF4IC1_EPI4:    br i1 [[CMP_N:%.*]], label %[[EXIT_LOOPEXIT:.*]], label %[[VEC_EPILOG_ITER_CHECK:.*]], !prof [[PROF7:![0-9]+]]
+; MAINVF4IC1_EPI4:  [[VEC_EPILOG_ITER_CHECK]]:
+; MAINVF4IC1_EPI4:    br i1 [[MIN_EPILOG_ITERS_CHECK:%.*]], label %[[VEC_EPILOG_SCALAR_PH]], label %[[VEC_EPILOG_PH]], !prof [[PROF8:![0-9]+]]
+; MAINVF4IC1_EPI4:  [[VEC_EPILOG_PH]]:
+; MAINVF4IC1_EPI4:    br label %[[VEC_EPILOG_VECTOR_BODY:.*]]
+; MAINVF4IC1_EPI4:  [[VEC_EPILOG_VECTOR_BODY]]:
+; MAINVF4IC1_EPI4:    br i1 [[TMP12:%.*]], label %[[VEC_EPILOG_MIDDLE_BLOCK:.*]], label %[[VEC_EPILOG_VECTOR_BODY]], !prof [[PROF9:![0-9]+]], !llvm.loop [[LOOP10:![0-9]+]]
----------------
fhahn wrote:

I think it would be helpful if we had at least the exit condition for the vector loop and the induction increment, but I'm not sure if it would be easy to include.

https://github.com/llvm/llvm-project/pull/144682