> By the time we do CorePrep, the hi files should already have been written.

I don't think so. When we generate real code we write the interface after the backend has generated the output object. See Note [Writing interface files] in GHC.Driver.Main

Cheers,
Sylvain

Hi Ben,

The -ddump-if-trace output is attached here. The error is produced
when compiling GHC.Types in ghc-prim.

Note that interface files are written after the Core pipeline is run.

Sorry for the confusion, I didn't mean the Core simplifier pipeline. I
mean the "Core -> Iface -> Core" roundtrip I tried to perform using
the output of CorePrep. By the time we do CorePrep, the hi files
should already have been written.

On Wed, Sep 16, 2020 at 11:48 PM Ben Gamari <ben@smart-cactus.org> wrote:

Cheng Shao <cheng.shao@tweag.io> writes:

Hi all,

Following a short chat in #ghc last week, I did a first attempt of
reusing existing Iface logic to implement serialization for
codegen-related Core. The implementation is included in the attached
patch (~100 loc). As a quick and dirty validation of whether it works,
I also modified the codegen pipeline logic to do a roundtrip: after
CorePrep, the Core bits are converted to Iface, then we immediately
convert it back and use it for later compiling.

With the patch applied, stage-1 GHC would produce a "missing hi file"
error like:

: Bad interface file: _build/stage1/libraries/ghc-prim/build/GHC/Types.hi
      _build/stage1/libraries/ghc-prim/build/GHC/Types.hi:
openBinaryFile: does not exist (No such file or directory)

Hi Cheng,

Which module is being compiled when this error is produced? Could you
provide -ddump-if-trace output for the failing compilation?

The error surprises me, since by the time we perform the Core-to-Core
roundtrip, the .hi file should already have been written to disk. Is
there anything obviously wrong with the implementation? I'd appreciate
any pointers or further questions, thanks a lot!

Note that interface files are written after the Core pipeline is run.

Cheers,

- Ben

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