[LLVMdev] target specific ways to extend ConstantExpr

Yuan Lin yulin at nvidia.com
Mon Dec 17 20:51:45 PST 2012

That's an interesting idea. What are the essential differences between the new subclass and ConstantExpr? Will it end up like ConstantExpr? Or you want it to be ConstantExpr 'done right'?



-----Original Message-----
From: Eli Friedman [mailto:eli.friedman at gmail.com] 
Sent: Monday, December 17, 2012 5:40 PM
To: Yuan Lin
Cc: Chris Lattner; llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] target specific ways to extend ConstantExpr

On Mon, Dec 17, 2012 at 5:10 PM, Yuan Lin <yulin at nvidia.com> wrote:
> We cannot use bitcast because bitcast is a value preserving operation, 
> but the address space conversion operation we have is a bit-changing operation.
> Where will the bulk of work be? Can we make a ConstantExpr which has a 
> new Opcode (or reuse call) and a list of operands? The first operand 
> is a string.

I would suggest adding a new subclass to Constant; that's closer to the direction we want to be moving in.  It'll look somewhat similar to ConstantExpr, but you don't want to mess with the opcodes ConstantExpr uses, and messing with the existing ConstantExpr code to allow MDStrings as operands would probably be harder than writing a class from scratch.

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