[LLVMdev] Custom Opcodes versus built-in opcodes

[Villmow, Micah]

-----Original Message-----
From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
On Behalf Of Bill Wendling
Sent: Thursday, September 18, 2008 4:16 PM
To: LLVM Developers Mailing List
Subject: Re: [LLVMdev] Custom Opcodes versus built-in opcodes

On Thu, Sep 18, 2008 at 4:04 PM, Villmow, Micah <Micah.Villmow at amd.com>
wrote:
> I am using lowering instructions and using custom opcodes that I can
more
> easily directly map to my backend. These opcodes are then used to emit
a
> custom set of instructions into the MachineBasicBlock. I've been able
to get
> one to work correctly, however, I've ran into an issue where my second
one
> is being confused as a FRAMEADDR opcode instead of my opcode.
>
[snip]
>
> What I want to happen is to take the branch w/ condition codes and
convert
> it into a comparison and then a branch based on the result to the
BasicBlock
> in the Jump SDValue. What I expect to occur after this function
returns is
> for the SDValue that I created to be matched with my BRANCH_NZERO
> instruction in my InstrInfo.td file. Instead what is occurring is that
it is
> mapping it for some reason to the FRAMEADDR built-in instruction and
running
> LowerFRAMEADDR. Both instructions are enumerated to the same value,
but they
> are part of different namespaces.
>
That's the problem. The "LowerFRAMEADDR" is called depending on the
enumeration's value, not on the namespace it's in. I can think of two
ways to solve this:

a) Change the enumeration of your BRANCH_NZERO instructions, or
2) Add your BRANCH_NZERO to the same namespace as FRAMEADDR.

The problem with both of these solutions is that the opcodes are
dynamically generated with tablegen and thus I cannot change the
enumeration as I don't set the enumeration. Also changing the namespace
doesn't change the enumeration.

I think this can probably be classified as a bug in tablegen. It
shouldn't be generating enumerated opcode values with the same values as
built in opcodes.
-bw
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