[PATCH] Allow multiple modules with the same name to coexist in the module cache

[Richard Smith]

On 4 Apr 2014 09:09, "Ben Langmuir" <blangmuir at apple.com> wrote:
>
>
> On Apr 3, 2014, at 7:49 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>
>> On Thu, Apr 3, 2014 at 3:40 PM, Ben Langmuir <blangmuir at apple.com> wrote:
>>>
>>>
>>> On Mar 28, 2014, at 2:45 PM, Richard Smith <richard at metafoo.co.uk>
wrote:
>>>
>>>> On Fri, Mar 28, 2014 at 1:12 PM, Ben Langmuir <blangmuir at apple.com
> wrote:
>>>>>
>>>>> This patch allows multiple modules that have the same name to coexist
in the module cache.  To differentiate between two modules with the same
name, we will consider the path the module map file that they are defined
by* part of the 'key' for looking up the precompiled module (pcm file).
 Specifically, this patch renames the precompiled module (pcm) files from
>>>>>
>>>>> cache-path/<module hash>/Foo.pcm
>>>>>
>>>>> to
>>>>>
>>>>> cache-path/<module hash>/Foo-<hash of module map path>.pcm
>>>>
>>>>
>>>> From a high level, I don't really see why we need a second hash here.
Shouldn't the -I options be included in the <module hash>? If I build the
same module with different -I flags, that should resolve to different .pcm
files, regardless of whether it makes the module name resolve to a
different module.map file.
>>>>
>>>> Are you trying to cope with the case where the -I path finds multiple
module.map files defining the same module (where it's basically chance
which one will get built and used)? I don't really feel like this is the
right solution to that problem either -- we should remove the 'luck' aspect
and use some sane mechanism to determine which module.map files are loaded,
and in what order.
>>>>
>>>> Is this addressing some other case?
>>>>
>>>>
>>>>>
>>>>> In addition, I've taught the ASTReader to re-resolve the names of
imported modules during module loading so that if the header search context
changes between when a module was originally built and when it is loaded we
can rebuild it if necessary.  For example, if module A imports module B
>>>>>
>>>>> first time:
>>>>> clang -I /path/to/A -I /path/to/B ...
>>>>>
>>>>> second time:
>>>>> clang -I /path/to/A -I /different/path/to/B ...
>>>>>
>>>>> will now rebuild A as expected.
>>>>>
>>>>>
>>>>> * in the case of inferred modules, we use the module map file that
*allowed* the inference, not the __inferred_module.map file, since the
inferred file path is the same for every inferred module.
>>>>
>>>>
>>>>
>>>> Review comments on the patch itself:
>>>>
>>>>  +  /// the inferrence (e.g. contained 'module *') rather than the
virtual
>>>>
>>>> Typo 'inference', 'Module *'.
>>>>
>>>> +  /// For an explanaition of \p ModuleMap, see Module::ModuleMap.
>>>>
>>>> Typo 'explanation'.
>>>>
>>>> +  // safe becuase the FileManager is shared between the compiler
instances.
>>>>
>>>> Typo 'because'
>>>>
>>>> +  // the inferred module. If this->ModuleMap is nullptr, then we are
using
>>>> +  // -emit-module directly, and we cannot have an inferred module.
>>>>
>>>> I don't understand what this comment is trying to say. If we're using
-emit-module, then we were given a module map on the command-line; should
that not be referred to by this->ModuleMap? (Also, why 'this->'?) How can a
top-level module be inferred? Is that a framework-specific thing?
>>>>
>>>> +    StringRef ModuleMap = this->ModuleMap ?
this->ModuleMap->getName() : InFile;
>>>>
>>>> Please pick a different variable name rather than shadowing a member
of '*this' here.
>>>>
>>>> +    // Construct the name <ModuleName>-<hash of ModuleMapPath>.pcm
which should
>>>> +    // be globally unique to this particular module.
>>>> +    llvm::APInt Code(64, llvm::hash_value(ModuleMapPath));
>>>> +    SmallString<128> HashStr;
>>>> +    Code.toStringUnsigned(HashStr);
>>>>
>>>> Use base 36, like the module hash.
>>>
>>>
>>> I've attached an updated patch.  Changes since the previous one:
>>> 1. Fixed the typos and other issues Richard pointed out
>>> 2. I've added code to canonicalize the module map path (using
realpath); I was getting spurious failures on case-intensitive filesystems.
>>
>>
>> This part is probably not OK, because it'll do the wrong thing on some
build farms (where the canonical path is not predictable, but the path that
make_absolute returns is, by careful control of $PWD). I'll look into this
more, but will be traveling for the next couple of days.
>
>
> Okay, I have a better idea: I already store the actual module map path in
MODULE_MAP_FILE, so when that is read, we can just get a FileEntry for it
and compare to what header search finds for the current module (since
FileEntries are uniqued by inode).  That also means I can give a better
diagnostic with the module map paths rather than the pcm filenames.

Sounds great, thanks!

>>
>>> 3. I've moved the initialization of the MainFileID (in source manager)
from Execute() to BeginSourceFile(), since we are now potentially creating
file ids for module map files during pch loading and need to be able to
find the main file reliably to construct a correct include stack.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20140404/a29aedce/attachment.html>