[LLVMdev] Strange exception in SelectionDAGBuilder

[Talin]

On Sat, Sep 25, 2010 at 11:56 PM, nicolas geoffray <
nicolas.geoffray at gmail.com> wrote:

> Hi Talin,
>
> I think that the framework for GC assumes llvm.gcroot to be in the first
> block. If it is not the case in your example, it will break these
> assumptions.
>
> Ah, that would explain it. Thanks.

Nicolas
>
> On Sun, Sep 26, 2010 at 1:38 AM, Talin <viridia at gmail.com> wrote:
>
>>  I'm working on the code to handle GC tracing of "intermediate values" (as
>> described in the GC doc), and I've run into a weird problem. (Note, this has
>> nothing to do with the patch I have proposed, this error occurs with regular
>> old pointer-allocas.)
>>
>> The exception I am getting occurs in this code here in
>> SelectionDAGBuilder.cpp:
>>
>> *case* *Intrinsic*::gcroot:
>>
>>     *if* (GFI) {
>>       *const* Value *Alloca = I.getArgOperand(0);
>>       *const* Constant *TypeMap = cast<Constant>(I.getArgOperand(1));
>> *      FrameIndexSDNode *FI = cast<FrameIndexSDNode>(getValue(Alloca).getNode());*      GFI->addStackRoot(FI->getIndex(), TypeMap);
>>     }
>>     *return* 0;
>>
>> Specifically, the cast from SDNode to FrameIndexSDNode fails because the
>> node type is DYNAMIC_STACKALLOC, while this code is expecting the node type
>> to be "FrameIndex" or "TargetFrameIndex". (I don't know what either of these
>> mean, I'm just telling you what the debugger is telling me.)
>>
>> Here's what the IR looks like:
>>
>>   %gc_root = alloca %tart.collections.KeyError*, align 8, !dbg !55084
>>   store %tart.collections.KeyError* %7, %tart.collections.KeyError**
>> %gc_root, align 8, !dbg !55084
>>   %9 = bitcast %tart.collections.KeyError** %gc_root to i8**, !dbg !55084
>>   call void @llvm.gcroot(i8** %9, i8* null), !dbg !55084
>>
>> As you can see, it's just creating an alloca of a pointer, bitcasting it
>> to i8**, and passing it to llvm.gcroot, just like it does in a hundred other
>> places. But in this place, for some reason, the SelectionDAGBuilder isn't
>> working.
>>
>> I just sync'd to the most recent LLVM head and I still get the error.
>>
>> --
>> -- Talin
>>
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>>
>>
>


-- 
-- Talin
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