Tim Armstrong created IMPALA-6926:
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Summary: Don't use CodegenOptLevel::None on release builds
Key: IMPALA-6926
URL: https://issues.apache.org/jira/browse/IMPALA-6926
Project: IMPALA
Issue Type: Improvement
Components: Backend
Affects Versions: Impala 2.12.0
Reporter: Tim Armstrong
Assignee: Joe McDonnell
This code adds some unnecessary divergence between the codegen'd code for debug
and release builds.
{code}
#ifndef NDEBUG
// For debug builds, don't generate JIT compiled optimized assembly.
// This takes a non-neglible amount of time (~.5 ms per function) and
// blows up the fe tests (which take ~10-20 ms each).
opt_level = llvm::CodeGenOpt::None;
#endif
{code}
Ideally LLVM will generate correct code in both cases (and we won't
accidentally have undefined behaviour in our code that could be exploited), but
that isn't always a safe assumption, e.g. IMPALA-6764. The above #ifdef doesn't
the effort required to get coverage for correctness of codegen'd code, since we
need to run the same test for debug and release builds. More specifically, the
random query generator is usually run against debug builds so that it will be
able to hit DCHECKs, but that means we're not verifying the correctness of the
generated code for a release build.
We should re-evaluate the above code. A few observations:
* The frontend tests shouldn't be doing codegen - almost all expressions being
evaluated should be interpreted. So the comment may not be accurate any more.
* The backend tests like expr-test may take significantly longer. I did a quick
experiment which seemed to indicate that it added a few minutes. We could
potentially leave the optimisation disabled for backend tests only
* Query tests could spend a bit longer in codegen. We would have to quantify it
but it probably isn't too bad.
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