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

Tue Mar 16 22:22:25 PDT 2021

xiangzhangllvm added a comment.

In D98757#2630844 <https://reviews.llvm.org/D98757#2630844>, @LuoYuanke wrote:

> Probably we need a .ll test case to for constant folding.

Fold constant is done in CSE and SCCP which are both passes run in Clang (O2 <https://reviews.llvm.org/owners/package/2/>)

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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.
----------------
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.

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

https://reviews.llvm.org/D98757