[PATCH] Update optimization passes to handle inalloca arguments

[Reid Kleckner]

Post-holiday ping.


On Fri, Dec 20, 2013 at 9:54 AM, Reid Kleckner <rnk at google.com> wrote:

> Sure!  The motivation is to properly implement non-trivial pass-by-value
> arguments in the Microsoft C++ ABI.  Without inalloca, it's impossible to
> represent the desired behavior in LLVM IR.  Specifically, we need to be
> able to call copy constructors on outgoing argument memory, or even better,
> elide the copy altogether and sret into it.
>
> There's a longer document here:
> http://llvm.org/docs/InAlloca.html
>
> I think this bug covers it the best:
> http://llvm.org/bugs/show_bug.cgi?id=5064
>
>
> On Fri, Dec 20, 2013 at 9:42 AM, Philip Reames <listmail at philipreames.com>wrote:
>
>>  Reid,
>>
>> Out of curiosity, what's the motivation behind inalloca?  I found your
>> update to the documentation which described their semantics, but I didn't
>> find any discussion of when "inalloc" parameters would actually be useful.
>> Could you point me to the appropriate discussion thread?  Just trying to
>> understand the motivation for the changes.
>>
>> Philip
>>
>>
>> On 12/19/13 2:43 PM, Reid Kleckner wrote:
>>
>> I searched Transforms/ and Analysis/ for 'ByVal' and updated those call
>> sites to check for inalloca if appropriate.
>>
>> I added tests for any change that would allow an optimization to fire on
>> inalloca.
>> http://llvm-reviews.chandlerc.com/D2449
>>
>> Files:
>>   include/llvm/IR/Argument.h
>>   include/llvm/IR/Instructions.h
>>   include/llvm/Support/CallSite.h
>>   lib/Analysis/MemoryBuiltins.cpp
>>   lib/Analysis/ValueTracking.cpp
>>   lib/IR/Function.cpp
>>   lib/IR/Instructions.cpp
>>   lib/Transforms/IPO/ArgumentPromotion.cpp
>>   lib/Transforms/IPO/DeadArgumentElimination.cpp
>>   lib/Transforms/IPO/FunctionAttrs.cpp
>>   lib/Transforms/IPO/IPConstantPropagation.cpp
>>   lib/Transforms/InstCombine/InstCombineCalls.cpp
>>   lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
>>   lib/Transforms/ObjCARC/ObjCARC.h
>>   lib/Transforms/Scalar/DeadStoreElimination.cpp
>>   test/Transforms/ArgumentPromotion/inalloca-2.ll
>>   test/Transforms/ArgumentPromotion/inalloca.ll
>>   test/Transforms/DeadStoreElimination/simple.ll
>>   test/Transforms/FunctionAttrs/readattrs.ll
>>
>>
>>
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>>
>>
>>
>
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