[LLVMdev] target specific ways to extend ConstantExpr

Yuan Lin yulin at nvidia.com
Mon Dec 17 17:10:42 PST 2012

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.

From: Chris Lattner [mailto:clattner at apple.com]
Sent: Monday, December 17, 2012 4:39 PM
To: Yuan Lin
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] target specific ways to extend ConstantExpr

On Dec 17, 2012, at 4:23 PM, Yuan Lin <yulin at nvidia.com<mailto:yulin at nvidia.com>> wrote:

The particular case we are looking at is converting a pointer from one address space to another address space. There is one operand and one output, both are the same pointer type, except for their address space. The pointers are of the same size. The operation is a bit-changing operation.
 We are using intrinsic functions for the instructions. We need a solution for the ConstantExpr.

Sounds like a bitcast to me.  Is there a reason the bitcast constexpr isn't working for you?

Instead of adding one target specific expression, it would be better to have a more generic scheme in LLVM.

I agree!  However, fixing this is also a lot of work.


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