hdelan added inline comments.
================
Comment at: clang/lib/Driver/ToolChains/Cuda.cpp:433
} else {
- // If no -O was passed, pass -O0 to ptxas -- no opt flag should correspond
- // to no optimizations, but ptxas's default is -O3.
- CmdArgs.push_back("-O0");
+ // If no -O was passed, pass -O3 to ptxas -- this makes ptxas's
+ // optimization level the same as the ptxjitcompiler.
----------------
tra wrote:
> I think this would be contrary to the expectation that lack of `-O` in clang
> means - `do not optimize` and it generally implies the whole compilation
> chain, including assembler. Matching whatever nvidia tools do is an
> insufficient reason for breaking this assumption, IMO.
>
> If you do want do run optimized ptxas on unoptimized PTX, you can use
> `-Xcuda-ptxas -O3`.
I think for the average user, consistency across the `ptxjitcompiler` and
`ptxas` is far more important than assuming that no `-O` means no optimization.
I think most users will assume that no `-O` will assume that whatever tools
being used will take their default optimization level, which in the case of
clang is `-O0` and in the case of `ptxas` is `-O3`.
We have had a few bugs with `ptxas`/`ptxjitcompiler` at higher optimization
levels, which were quite hard to pin down since offline `ptxas` and
`ptxjitcompiler` were using different optimisation levels, making bugs appear
in one and not the other. Of course we are aware of this now but this
inconsistency can result in bugs that are difficult to diagnose. Having
consistency between the `ptxjitcompiler` and `ptxas` is therefore of practical
benefit. Whereas if we are to leave it as is, with `ptxas` defaulting to `-O0`,
the benefit is purely semantic and not practical.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D116583/new/
https://reviews.llvm.org/D116583
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