dblaikie added inline comments.
================
Comment at: clang/lib/Serialization/ModuleManager.cpp:183
// Get a buffer of the file and close the file descriptor when done.
- Buf = FileMgr.getBufferForFile(NewModule->File, /*isVolatile=*/false);
+ Buf = FileMgr.getBufferForFile(NewModule->File, /*isVolatile=*/true);
}
----------------
vsapsai wrote:
> dexonsmith wrote:
> > rsmith wrote:
> > > dexonsmith wrote:
> > > > vsapsai wrote:
> > > > > Made this change because if we don't have a valid module but opened a
> > > > > corresponding .pcm file earlier, there is a high chance that .pcm
> > > > > file was rebuilt.
> > > > Please add a comment in the code explaining that.
> > > This change is proving really bad for us. This prevents using `mmap` for
> > > loading module files, and instead forces the entire file to be loaded
> > > every time. Please revert.
> > Can we limit the revert to explicit vs. implicit module builds? The
> > scenario Volodymyr was defending against is implicit-only.
> Richard, can you please tell what is your modules configuration and how you
> are invoking clang? For implicit builds loading a module instead of `mmap` is
> still better than building a module. But for explicit modules I see there is
> no need to use `isVolatile` as modules aren't changing all the time.
Richard/Google use explicit modules, if that's the particular parameter you're
asking about.
So, yes, for Google's needs a solution that allows mmap to continue to be used
for explicit modules would suffice, I believe.
(not to in any way derail that from being addressed - I thought implicit
modules weren't race-y - they're hashed, etc, so they shouldn't collide/be
overwritten? Seems like a loss in performance to have to copy the whole thing
into memory rather than using mmap, if that could be avoided by more precise
hashing/collision avoidance?)
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D72860/new/
https://reviews.llvm.org/D72860
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