[PATCH] D98757: [AMX] Not fold constant bitcast into amx intrisic

Tue Mar 16 22:59:20 PDT 2021

xiangzhangllvm added inline comments.

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Comment at: llvm/lib/Analysis/ConstantFolding.cpp:101
 /// Constant fold bitcast, symbolically evaluating it with DataLayout.
 /// This always returns a non-null constant, but it may be a
 /// ConstantExpr if unfoldable.
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clin1 wrote:
> xiangzhangllvm wrote:
> > clin1 wrote:
> > > API for this function always returns non-null: can we return ConstantExpr::getBitCast(C,DestTy) instead? Then the change in SCCP is not needed either.
> > I tried, the SCCP will also fold the bitcast into the following instruction.
> I see, that makes sense. But are we sure that all callers of FoldBitCast are doing a null check: for example, FoldReinterpretLoadFromConstPtr calls FoldBitCast several times, and null is not checked before dereference. Maybe the AMX type cannot happen in this case?
> Alternative: can AMX be checked in SCCP?
Right! let me check the callers of FoldBitCast,
Luckly, there is only several callers of FoldBitCast, and almost all in this file ConstantFolding.cpp.

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  https://reviews.llvm.org/D98757/new/

https://reviews.llvm.org/D98757