[LLVMdev] Adding a new instruction to Alpha ISA

[Giang Hoang]

Hi,

I want to add an extra instruction to the Alpha ISA.  This is not a new
operation; it is just an addition with a lower latency, let's call it
fast-add.  Could you give me advice on what's an easy and clean approach to
this?  I am thinking of adding an extra instruction to the LLVM IR to
represent this fast-add operation (I want to make the decision of using
either the normal addition or fast addition during loop unroll pass, which
happens before code generation; so I think I need an extra IR instruction).
 The LLVM documentation warns against adding new IR instruction unless it is
absolutely necessary, so I would like to ask to make sure.

Thank you very much.

Giang
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