[LLVMdev] Methods on addrspace pointers

[Matt Arsenault]

On 01/20/2014 02:51 PM, Brandon Holt wrote:
> I've been developing an optimization pass that uses the address space 
> attribute (__attribute__((address_space(200))) to indicate different 
> kinds of pointers to be treated differently (I'm making them be 
> pointers to a "global" address space as in UPC).
>
> However, I've hit a snag in the frontend code generator: if I try to 
> make a method call on a pointer with a custom address space, the 
> frontend chokes because it can't bitcast between different address 
> spaces, and methods are functions that take a pointer to "this" which 
> is assumed to be in addrspace(0):
>
>> Assertion failed: (castIsValid(op, S, Ty) && "Invalid cast!"), 
>> function Create, file ../lib/IR/Instructions.cpp, line 2352.
>> 0  clang-3.4                0x00000001039527f8 
>> llvm::sys::PrintStackTrace(__sFILE*) + 40
>> 1  clang-3.4                0x0000000103952c54 SignalHandler(int) + 388
>> 2  libsystem_platform.dylib 0x00007fff802395aa _sigtramp + 26
>> 3  libsystem_platform.dylib 000000000000000000 _sigtramp + 2145151600
>> 4  clang-3.4                0x0000000103952ab6 abort + 22
>> 5  clang-3.4                0x0000000103952a91 __assert_rtn + 81
>> 6  clang-3.4                0x000000010385f8bf 
>> llvm::CastInst::Create(llvm::Instruction::CastOps, llvm::Value*, 
>> llvm::Type*, llvm::Twine const&, llvm::Instruction*) + 687
>> 7  clang-3.4                0x00000001030a4d1c llvm::IRBuilder<true, 
>> llvm::ConstantFolder, llvm::IRBuilderDefaultInserter<true> 
>> >::CreateCast(llvm::Instruction::CastOps, llvm::Value*, llvm::Type*, 
>> llvm::Twine const&) + 76
>> 8  clang-3.4                0x0000000103bbeac3 
>> clang::CodeGen::CodeGenFunction::EmitCall(clang::CodeGen::CGFunctionInfo 
>> const&, llvm::Value*, clang::CodeGen::ReturnValueSlot, 
>> clang::CodeGen::CallArgList const&, clang::Decl const*, 
>> llvm::Instruction**) + 3075
>> 9  clang-3.4                0x0000000103c11c02 
>> clang::CodeGen::CodeGenFunction::EmitCXXMemberCall(clang::CXXMethodDecl 
>> const*, clang::SourceLocation, llvm::Value*, 
>> clang::CodeGen::ReturnValueSlot, llvm::Value*, llvm::Value*, 
>> clang::QualType, clang::ConstExprIterator, clang::ConstExprIterator) 
>> + 738
>
> I know it is not actually expected to be correct behavior to use other 
> addrspace pointers in place of addrspace(0) pointers. My 
> transformation passes change these calls, but I don't get a chance to 
> make the change because the frontend chokes first.
>
> My questions are:
> 1. Is there a more graceful way that these bitcasts could be handled? 
> Code to load/store from alternate address spaces is allowed to be 
> generated, it just segfaults when run. Can the same behavior be 
> allowed without breaking things for method calls to these pointers? I 
> can imagine simply adding code to detect if the address space is wrong 
> and applying an addrspace cast to get around it.
Since 3.4 you need to use the addrspacecast instruction to cast between 
address spaces. It's possible there are still some places left that 
haven't been fixed yet to use it instead of creating bitcasts.

>
> 2. Is there a way to create methods that can be called with pointers 
> to different address spaces? It seems there is no way to declare these 
> in C++ using GNU attributes, and addrspace() seems to not be supported 
> by C++11 attribute syntax, which could possibly express this.
You can use __attribute__((address_space(N))

>
> Thanks,
> -Brandon
>
> --
> Brandon Holt
> Grad student @ University of Washington
> http://homes.cs.washington.edu/~bholt 
> <http://homes.cs.washington.edu/%7Ebholt>
>
>
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