llvm dev - Mar 2010 - [LLVMdev] SelectionDAG constant folding leads to assertion failure

My experimental code calls DAG.getNode to construct a unary node with
a flag result. Unfortunately the argument turns out to be constant, so
lib/CodeGen/SelectionDAG/SelectionDAG.cpp:2332 calls VT.getSizeInBits
on the flag type, which isSimple(), so we call V.getSizeInBits at
ValueTypes.h:560 and fail at ValueTypes.h:240:

clang: .../include/llvm/CodeGen/ValueTypes.h:240: unsigned int
llvm::MVT::getSizeInBits() const: Assertion `0 && "getSizeInBits
called
on extended MVT."' failed.

The message is misleading as Flag is not an extended MVT.

I would guess that normally constant folding would have happened
earlier on, but it would be nice if I could call DAG.getNode with
constant arguments without this happening.

Could getSizeInBits() return 0 or -1 for a Flag? Or should
SelectionDAG::getNode not call getSizeInBits until it knows it
actually needs the value?






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On Mar 15, 2010, at 8:54 AM, Edmund Grimley Evans wrote:
> My experimental code calls DAG.getNode to construct a unary node with
> a flag result. Unfortunately the argument turns out to be constant, so
> lib/CodeGen/SelectionDAG/SelectionDAG.cpp:2332 calls VT.getSizeInBits
> on the flag type, which isSimple(), so we call V.getSizeInBits at
> ValueTypes.h:560 and fail at ValueTypes.h:240:
That's bad. :)
> Or should
> SelectionDAG::getNode not call getSizeInBits until it knows it
> actually needs the value?
You're right, fixed in r98547, thanks!

-Chris