[mlir] Assertion `detail::isPresent(Val) && "dyn_cast on a non-existent value"' failed.

git version: 5492d06d4fb99795b3b7247be374cdcb47f5ac03

system: `Ubuntu 18.04.6 LTS`

reproduce with: `mlir-opt -convert-openmp-to-llvm -convert-vector-to-llvm -acc-implicit-data a.mlir`

a.mlir:

```mlir
module {
func.func @test(%arg0: memref<10xf32>, %arg1: index) {
%0 = acc.create varPtr(%arg0 : memref<10xf32>) -> memref<10xf32>
acc.serial dataOperands(%0 : memref<10xf32>) {
%c0 = arith.constant 0 : index
%c0_0 = arith.constant 0 : index
%1 = arith.cmpi sge, %arg1, %c0 : index
%2 = arith.cmpi slt, %arg1, %c0 : index
%3 = arith.andi %1, %2 : i1
cf.assert %3, "ERROR: Runtime op verification failed\0A%7 = \22memref.load\22(%arg1, %arg2) : (memref<10xf32>, index) -> f32\0A^ out-of-bounds access\0ALocation: loc(\22/data/szy/MLIR/seed729/tmp.fJQ9P1y8uQ.mlir\22:2:8)"
%4 = memref.load %arg0[%arg1] : memref<10xf32>
acc.yield
}
return
}
}

```

stack trace:

```
mlir-opt: /data/szy/MLIR/llvm-release/llvm-project/llvm/include/llvm/Support/Casting.h:656: decltype(auto) llvm::dyn_cast(From *) [To = mlir::acc::CopyinOp, From = mlir::Operation]: Assertion `detail::isPresent(Val) && "dyn_cast on a non-existent value"' 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 -convert-openmp-to-llvm -convert-vector-to-llvm -acc-implicit-data 58.mlir
#0 0x0000556dc5ca10f8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20300f8)
#1 0x0000556dc5c9df91 llvm::sys::RunSignalHandlers() (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x202cf91)
#2 0x0000556dc5ca2216 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0x00007fe14dbdc420 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14420)
#4 0x00007fe14d21900b raise /build/glibc-LcI20x/glibc-2.31/signal/../sysdeps/unix/sysv/linux/raise.c:51:1
#5 0x00007fe14d1f8859 abort /build/glibc-LcI20x/glibc-2.31/stdlib/abort.c:81:7
#6 0x00007fe14d1f8729 get_sysdep_segment_value /build/glibc-LcI20x/glibc-2.31/intl/loadmsgcat.c:509:8
#7 0x00007fe14d1f8729 _nl_load_domain /build/glibc-LcI20x/glibc-2.31/intl/loadmsgcat.c:970:34
#8 0x00007fe14d209fd6 (/lib/x86_64-linux-gnu/libc.so.6+0x33fd6)
#9 0x0000556dc7aa98bc mlir::acc::getBounds(mlir::Operation*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x3e388bc)
#10 0x0000556dc66973c4 (anonymous namespace)::fillInBoundsForUnknownDimensions(mlir::Operation*, mlir::OpBuilder&) ACCImplicitData.cpp:0:0
#11 0x0000556dc6695350 (anonymous namespace)::ACCImplicitData::runOnOperation()::$_0::operator()(mlir::Operation*) const ACCImplicitData.cpp:0:0
#12 0x0000556dc5d62ece void mlir::detail::walk(mlir::Operation*, llvm::function_ref, mlir::WalkOrder) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20f1ece)
#13 0x0000556dc5d62ece void mlir::detail::walk(mlir::Operation*, llvm::function_ref, mlir::WalkOrder) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20f1ece)
#14 0x0000556dc6690595 (anonymous namespace)::ACCImplicitData::runOnOperation() ACCImplicitData.cpp:0:0
#15 0x0000556dce64c502 mlir::detail::OpToOpPassAdaptor::run(mlir::Pass*, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xa9db502)
#16 0x0000556dce64d344 mlir::detail::OpToOpPassAdaptor::runPipeline(mlir::OpPassManager&, mlir::Operation*, mlir::AnalysisManager, bool, unsigned int, mlir::PassInstrumentor*, mlir::PassInstrumentation::PipelineParentInfo const*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xa9dc344)
#17 0x0000556dce65425a mlir::PassManager::runPasses(mlir::Operation*, mlir::AnalysisManager) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xa9e325a)
#18 0x0000556dce653b8f mlir::PassManager::run(mlir::Operation*) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0xa9e2b8f)
#19 0x0000556dc5d503d0 performActions(llvm::raw_ostream&, std::shared_ptr const&, mlir::MLIRContext*, mlir::MlirOptMainConfig const&) MlirOptMain.cpp:0:0
#20 0x0000556dc5d4f606 llvm::LogicalResult llvm::function_ref>, llvm::MemoryBufferRef const&, llvm::raw_ostream&)>::callback_fn>, mlir::DialectRegistry&, mlir::MlirOptMainConfig const&)::$_0>(long, std::unique_ptr>, llvm::MemoryBufferRef const&, llvm::raw_ostream&) MlirOptMain.cpp:0:0
#21 0x0000556dce9a08a5 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+0xad2f8a5)
#22 0x0000556dc5d46666 mlir::MlirOptMain(llvm::raw_ostream&, std::unique_ptr>, mlir::DialectRegistry&, mlir::MlirOptMainConfig const&) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20d5666)
#23 0x0000556dc5d46a45 mlir::MlirOptMain(int, char**, llvm::StringRef, llvm::StringRef, mlir::DialectRegistry&) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20d5a45)
#24 0x0000556dc5d46da5 mlir::MlirOptMain(int, char**, llvm::StringRef, mlir::DialectRegistry&) (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20d5da5)
#25 0x0000556dc5c86b82 main (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x2015b82)
#26 0x00007fe14d1fa083 __libc_start_main /build/glibc-LcI20x/glibc-2.31/csu/../csu/libc-start.c:342:3
#27 0x0000556dc5c866be _start (/data/szy/MLIR/llvm-release/llvm-project/build/bin/mlir-opt+0x20156be)
Aborted (core dumped)
```

Run the reported mlir-opt command with the supplied a.mlir reproducer and inspect the ACCImplicitData.cpp frames in the stack trace, especially fillInBoundsForUnknownDimensions and the call to mlir::acc::getBounds. Determine why the pass reaches dyn_cast with a missing value; done means the reproducer no longer aborts and the regression is covered by an appropriate test.

Written by the indexing model from the issue text.