[llvm] [NFC][VPlan] Extract BTC-related tests into `vplan-based-stride-mv-btc.ll` (PR #214047)

[Florian Hahn via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals none --version 6
+
+; This file complements vplan-based-stride-mv.ll by containing the test
+; functions from VPlan/vplan-based-stride-mv.ll that focus on interactions
+; between stride speculation and backedge taken count as we want to look/verify
+; both fixed and scalable vector width vectorization.
+
+; RUN: opt < %s -p loop-vectorize -force-vector-width=4 -S \
+; RUN:     -enable-mem-access-versioning=false  2>&1 | FileCheck %s --check-prefix COMPARE-NO-MV
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fhahn wrote:

AFAICT there's no check lines for stderr, so there should eb no need for `2>&1`?

https://github.com/llvm/llvm-project/pull/214047