llvm dev - Jun 2011 - [LLVMdev] ARM thumb-2 instruction used for non-thumb2 CPUs

On Jun 22, 2011, at 3:16 PM, Renato Golin wrote:
> On 22 June 2011 11:49, Damjan Marion <damjan.marion at gmail.com>
wrote:
>> # /opt/llvm/bin/clang -S -ccc-host-triple arm-unknown-freebsd
-mcpu=arm926ej-s -mfloat-abi=soft -v -o rrx.S rrx.c
> 
> Even though you specified cpu as arm9, it's probably generating
> generic ARM IR (use -emit-llvm -S and see), which defaults to ARM
> instructions.
> 
> If you want thumb, use triple = thumb-unknown-freebsd, but still, that
> will have problems. You can do it in two steps (clang -> IR, llc ->
> ASM) and specify all options on both steps, or wait until the clang
> patch for cross-compilation is reviewed and applied.

Hi Renato,

I dont want to generate Thumb code, actually i missed in my previous email that
"rrx r0,r0" is both ARM and thumb-2 instruction, but only defined in
ARMv7.

llvm produces "rrx r0,r0" mnemonics for ARMv5 targets, however ARM
Architecture Reference Manual for ARMv5 doesn't know about that mnemonics.
There is equivalent mnemonics on ARMv5: "mov r0,r0, rrx"

both "rrx r0,r0" and "mov r0, r0, rrx" result in same
opcode: 0xe1a00060.

Problem is that in case when old binutils are used (in my case freebsd is using
old one due to license upgrade to GPLv3) AS doesn't understand new mnemonics
and fails.

Can we change to old mnemonic at least when ARMv4 and ARMv5 code is generated?

Thanks,

On 22 June 2011 14:33, Damjan Marion <damjan.marion at gmail.com>
wrote:
> Problem is that in case when old binutils are used (in my case freebsd is
using old one due to license upgrade to GPLv3) AS doesn't understand new
mnemonics and fails.
Indeed, this is new in ARM ARM v7.

> Can we change to old mnemonic at least when ARMv4 and ARMv5 code is
generated?
We definitely should. Feel free to send a patch if you already have,
or create a bug in bugzilla. Shouldn't be too hard to add it.

cheers,
--renato

On Jun 22, 2011, at 4:22 PM, Renato Golin wrote:
>> Can we change to old mnemonic at least when ARMv4 and ARMv5 code is
generated?
> 
> We definitely should. Feel free to send a patch if you already have,
> or create a bug in bugzilla. Shouldn't be too hard to add it.
I can try to create patch, however I'm still new to llvm.
Can you give me some brief hints where to start?

Thanks,

Damjan

On Jun 22, 2011, at 7:22 AM, Renato Golin wrote:
> On 22 June 2011 14:33, Damjan Marion <damjan.marion at gmail.com>
wrote:
>> Problem is that in case when old binutils are used (in my case freebsd
is using old one due to license upgrade to GPLv3) AS doesn't understand new
mnemonics and fails.
> 
> Indeed, this is new in ARM ARM v7.
> 
> 
>> Can we change to old mnemonic at least when ARMv4 and ARMv5 code is
generated?
> 
> We definitely should. Feel free to send a patch if you already have,
> or create a bug in bugzilla. Shouldn't be too hard to add it.
LLVM always uses unified syntax, including updated mnemonics for older
instructions. Older binutils aren't supported. This is unlikely to change.

-Jim