[llvm] r198349 - Allow addrspacecast in global aliases

[Matt Arsenault]

On 01/14/2014 04:20 PM, Owen Anderson wrote:
> I don't know Matt's intent here, but some GPUs support accessing local 
> memory via a memory mapping inside global memory, in addition to via 
> direct access.  This has the nice benefit of still allowing direct 
> access (which might be more efficient) while simplifying the 
> programming model by allowing precompiled functions with pointer 
> parameters not to have to be specialized for each address space.
>
> --Owen
This is about what I was thinking. Newer GPUs have a flat address space 
available, so either a pointer with the correct address space or a 
generic pointer could be used to access an object.

>
> On Jan 14, 2014, at 04:15 PM, Rafael Espíndola 
> <rafael.espindola at gmail.com> wrote:
>
>> Sorry I missed this before.
>>
>> Why do you need this? Aliases are just another name for a given
>> position, so it seems strange to have the same position being in two
>> address spaces.
>>
>> How do you see this interacting with the proposed solution for
>> http://llvm.org/bugs/show_bug.cgi?id=10367?
>>
>> On 2 January 2014 12:55, Matt Arsenault <Matthew.Arsenault at amd.com 
>> <mailto:Matthew.Arsenault at amd.com>> wrote:
>>> Author: arsenm
>>> Date: Thu Jan 2 14:55:01 2014
>>> New Revision: 198349
>>> URL: http://llvm.org/viewvc/llvm-project?rev=198349&view=rev
>>> Log:
>>> Allow addrspacecast in global aliases
>>> Added:
>>> llvm/trunk/test/Assembler/addrspacecast-alias.ll
>>> Modified:
>>> llvm/trunk/lib/IR/Globals.cpp
>>> llvm/trunk/lib/IR/Verifier.cpp
>>> Modified: llvm/trunk/lib/IR/Globals.cpp
>>> URL: 
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Globals.cpp?rev=198349&r1=198348&r2=198349&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/IR/Globals.cpp (original)
>>> +++ llvm/trunk/lib/IR/Globals.cpp Thu Jan 2 14:55:01 2014
>>> @@ -237,7 +237,8 @@ GlobalValue *GlobalAlias::getAliasedGlob
>>> return GV;
>>> ConstantExpr *CE = cast<ConstantExpr>(C);
>>> - assert((CE->getOpcode() == Instruction::BitCast ||
>>> + assert((CE->getOpcode() == Instruction::BitCast ||
>>> + CE->getOpcode() == Instruction::AddrSpaceCast ||
>>> CE->getOpcode() == Instruction::GetElementPtr) &&
>>> "Unsupported aliasee");
>>> Modified: llvm/trunk/lib/IR/Verifier.cpp
>>> URL: 
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Verifier.cpp?rev=198349&r1=198348&r2=198349&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/IR/Verifier.cpp (original)
>>> +++ llvm/trunk/lib/IR/Verifier.cpp Thu Jan 2 14:55:01 2014
>>> @@ -550,9 +550,11 @@ void Verifier::visitGlobalAlias(GlobalAl
>>> ConstantExpr *CE = dyn_cast<ConstantExpr>(Aliasee);
>>> Assert1(CE &&
>>> (CE->getOpcode() == Instruction::BitCast ||
>>> + CE->getOpcode() == Instruction::AddrSpaceCast ||
>>> CE->getOpcode() == Instruction::GetElementPtr) &&
>>> isa<GlobalValue>(CE->getOperand(0)),
>>> - "Aliasee should be either GlobalValue or bitcast of GlobalValue",
>>> + "Aliasee should be either GlobalValue, bitcast or "
>>> + "addrspacecast of GlobalValue",
>>> &GA);
>>> if (CE->getOpcode() == Instruction::BitCast) {
>>> Added: llvm/trunk/test/Assembler/addrspacecast-alias.ll
>>> URL: 
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Assembler/addrspacecast-alias.ll?rev=198349&view=auto
>>> ==============================================================================
>>> --- llvm/trunk/test/Assembler/addrspacecast-alias.ll (added)
>>> +++ llvm/trunk/test/Assembler/addrspacecast-alias.ll Thu Jan 2 
>>> 14:55:01 2014
>>> @@ -0,0 +1,6 @@
>>> +; RUN: llvm-as -disable-output %s
>>> +
>>> +; Test that global aliases are allowed to be constant addrspacecast
>>> +
>>> + at i = internal addrspace(1) global i8 42
>>> + at ia = alias internal i8 addrspace(2)* addrspacecast (i8 
>>> addrspace(1)* @i to i8 addrspace(2)*)
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