niyue commented on code in PR #40031:
URL: https://github.com/apache/arrow/pull/40031#discussion_r1485615504
##########
cpp/src/gandiva/engine.h:
##########
@@ -57,12 +58,11 @@ class GANDIVA_EXPORT Engine {
///
/// \param[in] config the engine configuration
/// \param[in] cached flag to mark if the module is already compiled and
cached
- /// \param[in] object_cache an optional object_cache used for building the
module
+ /// \param[in] object_cache an object_cache used for building the module
/// \return arrow::Result containing the created engine
static Result<std::unique_ptr<Engine>> Make(
const std::shared_ptr<Configuration>& config, bool cached,
- std::optional<std::reference_wrapper<GandivaObjectCache>> object_cache =
- std::nullopt);
+ llvm::ObjectCache* object_cache);
Review Comment:
There are two reasons I make this change for this constructor:
* I realize `GandivaObjectCache` is a higher level concept, to construct it,
`ExpressionCacheKey` needs to be used, and the caller needs to be aware of
concepts like `Schema`/`Configuration`/`Expression`, and `Engine` is lower
level and is not aware of these concepts at all. So I switch to use a lower
level API (`llvm::ObjectCache`) instead
* in this PR, I tries to avoid constructing too many `TargetMachine` for
better performance, a `TargetIRAnalysis` is passed to `Engine`'s constructor
(the Engine only uses `TargetIRAnalysis` during optimizing code, but doesn't
use `TargetMachine` directly). For some unknown reason (it seems to be a bug of
LLVM for me), the `TargetIRAnalysis` obtained from a `TargetMachine` requires
the `TargetMachine` instance to be alive when running optimization
(`OptimizeModuleWithNewPassManager`), so I change this object_cache to have a
default value if nullptr is provided (a cache that does not cache at all), and
the only place that constructs `Engine` without `object_cache` were several
unit tests in `engine_llvm_test.cc` and `llvm_generator_test.cc`, and the
corresponding `target_machine` will be moved into `TMOwningSimpleCompiler` and
be alive:
```
jit_builder.setCompileFunctionCreator(
[&object_cache, &target_machine](llvm::orc::JITTargetMachineBuilder
JTMB)
->
llvm::Expected<std::unique_ptr<llvm::orc::IRCompileLayer::IRCompiler>> {
// after compilation, the object code will be stored into the given
object
// cache
return std::make_unique<llvm::orc::TMOwningSimpleCompiler>(
std::move(target_machine), object_cache);
});
```
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