[mlir] Assertion `castSrcLastDim % castDstLastDim == 0' failed.

git version: 81a8c66fdc96a7bf6927bf3f88d4b2e24a5c71e7

system: `Ubuntu 18.04.6 LTS`

reproduce with: `mlir-opt -test-vector-break-down-bitcast a.mlir`

a.mlir:

```mlir
module {
func.func @f2(%arg0: vector<16xi16>) -> vector<3xi16> {
%0 = arith.trunci %arg0 : vector<16xi16> to vector<16xi3>
%1 = vector.bitcast %0 : vector<16xi3> to vector<3xi16>
return %1 : vector<3xi16>
}
}

```

stack trace:

```
mlir-opt: /data/szy/MLIR/llvm-release/llvm-project/mlir/lib/Dialect/Vector/Transforms/VectorTransforms.cpp:932: virtual LogicalResult (anonymous namespace)::BreakDownVectorBitCast::matchAndRewrite(vector::BitCastOp, PatternRewriter &) const: Assertion `castSrcLastDim % castDstLastDim == 0' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
Stack dump:
0. Program arguments: /data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt -test-vector-break-down-bitcast 84.mlir
#0 0x000055a4a0b080c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20360c8)
#1 0x000055a4a0b04f61 llvm::sys::RunSignalHandlers() (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x2032f61)
#2 0x000055a4a0b091e6 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0x00007fe9a1f3e420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
#4 0x00007fe9a157b00b raise /build/glibc-LcI20x/glibc-2.31/signal/../sysdeps/unix/sysv/linux/raise.c:51:1
#5 0x00007fe9a155a859 abort /build/glibc-LcI20x/glibc-2.31/stdlib/abort.c:81:7
#6 0x00007fe9a155a729 get_sysdep_segment_value /build/glibc-LcI20x/glibc-2.31/intl/loadmsgcat.c:509:8
#7 0x00007fe9a155a729 _nl_load_domain /build/glibc-LcI20x/glibc-2.31/intl/loadmsgcat.c:970:34
#8 0x00007fe9a156bfd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
#9 0x000055a4a75a26ee (anonymous namespace)::BreakDownVectorBitCast::matchAndRewrite(mlir::vector::BitCastOp, mlir::PatternRewriter&) const VectorTransforms.cpp:0:0
#10 0x000055a4a949527d void llvm::function_ref::callback_fn, llvm::function_ref, llvm::function_ref)::$_0>(long) PatternApplicator.cpp:0:0
#11 0x000055a4a9491bda mlir::PatternApplicator::matchAndRewrite(mlir::Operation*, mlir::PatternRewriter&, llvm::function_ref, llvm::function_ref, llvm::function_ref) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xa9bfbda)
#12 0x000055a4a946a4b4 (anonymous namespace)::GreedyPatternRewriteDriver::processWorklist() GreedyPatternRewriteDriver.cpp:0:0
#13 0x000055a4a9469532 void llvm::function_ref::callback_fn<(anonymous namespace)::RegionPatternRewriteDriver::simplify(bool*) &&::$_2>(long) GreedyPatternRewriteDriver.cpp:0:0
#14 0x000055a4a946651b mlir::applyPatternsGreedily(mlir::Region&, mlir::FrozenRewritePatternSet const&, mlir::GreedyRewriteConfig, bool*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xa99451b)
#15 0x000055a4a1358455 (anonymous namespace)::TestVectorBreakDownBitCast::runOnOperation() TestVectorTransforms.cpp:0:0
#16 0x000055a4a94f0662 mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa1e662)
#17 0x000055a4a94f14a4 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa1f4a4)
#18 0x000055a4a94fc02e auto void mlir::parallelForEach<__gnu_cxx::__normal_iterator>>, mlir::detail::OpToOpPassAdaptor::runOnOperationAsyncImpl(bool)::$_12>(mlir::MLIRContext*, __gnu_cxx::__normal_iterator>>, __gnu_cxx::__normal_iterator>>, mlir::detail::OpToOpPassAdaptor::runOnOperationAsyncImpl(bool)::$_12&&)::'lambda'(__gnu_cxx::__normal_iterator>>&&)::operator()(__gnu_cxx::__normal_iterator>>&&) const Pass.cpp:0:0
#19 0x000055a4a94f4158 mlir::detail::OpToOpPassAdaptor::runOnOperationAsyncImpl(bool) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa22158)
#20 0x000055a4a94f0847 mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa1e847)
#21 0x000055a4a94f14a4 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa1f4a4)
#22 0x000055a4a94f83ba mlir::PassManager::runPasses(mlir::Operation*, mlir::AnalysisManager) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa263ba)
#23 0x000055a4a94f7cef mlir::PassManager::run(mlir::Operation*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xaa25cef)
#24 0x000055a4a0bb73c0 performActions(llvm::raw_ostream&, std::shared_ptr const&, mlir::MLIRContext*, mlir::MlirOptMainConfig const&) MlirOptMain.cpp:0:0
#25 0x000055a4a0bb65f6 llvm::LogicalResult llvm::function_ref>, llvm::MemoryBufferRef const&, llvm::raw_ostream&)>::callback_fn>, mlir::DialectRegistry&, mlir::MlirOptMainConfig const&)::$_0>(long, std::unique_ptr>, llvm::MemoryBufferRef const&, llvm::raw_ostream&) MlirOptMain.cpp:0:0
#26 0x000055a4a9843e55 mlir::splitAndProcessBuffer(std::unique_ptr>, llvm::function_ref>, llvm::MemoryBufferRef const&, llvm::raw_ostream&)>, llvm::raw_ostream&, llvm::StringRef, llvm::StringRef) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xad71e55)
#27 0x000055a4a0bad656 mlir::MlirOptMain(llvm::raw_ostream&, std::unique_ptr>, mlir::DialectRegistry&, mlir::MlirOptMainConfig const&) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20db656)
#28 0x000055a4a0bada35 mlir::MlirOptMain(int, char**, llvm::StringRef, llvm::StringRef, mlir::DialectRegistry&) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20dba35)
#29 0x000055a4a0badd95 mlir::MlirOptMain(int, char**, llvm::StringRef, mlir::DialectRegistry&) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20dbd95)
#30 0x000055a4a0aedb52 main (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x201bb52)
#31 0x00007fe9a155c083 __libc_start_main /build/glibc-LcI20x/glibc-2.31/csu/../csu/libc-start.c:342:3
#32 0x000055a4a0aed68e _start (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x201b68e)
Aborted (core dumped)
```

Start with the assertion in mlir/lib/Dialect/Vector/Transforms/VectorTransforms.cpp and the TestVectorBreakDownBitCast entry point mentioned in the stack trace. Run mlir-opt -test-vector-break-down-bitcast on the provided a.mlir input; done means the input no longer aborts at the assertion and the regression behavior is covered.

Written by the indexing model from the issue text.