llvm dev - Aug 2012 - [LLVMdev] Question about arm thumb2 code generation

Hi all,

Does llc -march=thumb -mcpu=cortex-a9 enable generation of thumb2 code for armv7
?

Best Regards
Seb
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On Jul 27, 2012, at 9:04 AM, Sebastien DELDON-GNB <sebastien.deldon at
st.com> wrote:
> Hi all,
>  
> Does llc –march=thumb –mcpu=cortex-a9 enable generation of thumb2 code for
armv7 ?
That's how I usually do it.  Somewhere in the target description we
associate a9 with -mattr=+thumb2.

There are plenty of other ways to get the same result, and it's all very
confusing and opaque. Don't ask me what triples are valid. I usually verify
that I have the right command line by staring at the disassembly until I'm
convinced.

One good thing about llc (unlike other drivers... *cough*) is that the option
values are actually discoverable!

llc --version gives you -march= values.
llc -mcpu=help
llc -mattr=help

-Andy
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Thanks andrew for the answer.
I would like to generate code for Cortex-A9 that don't use neon for fp
computation but vfpv3 -d16. I've tried some combination of
-mattr=+neon,-neonfp,+vfp3,+d16 but couldn't get ".fpu vfpv3-d16"
directive generated in assembly file. Do you know how to make it happen ?

Best Regards
Seb

From: Andrew Trick [mailto:atrick at apple.com]
Sent: Saturday, July 28, 2012 2:46 AM
To: Sebastien DELDON-GNB
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Question about arm thumb2 code generation

On Jul 27, 2012, at 9:04 AM, Sebastien DELDON-GNB <sebastien.deldon at
st.com<mailto:sebastien.deldon at st.com>> wrote:


Hi all,

Does llc -march=thumb -mcpu=cortex-a9 enable generation of thumb2 code for armv7
?

That's how I usually do it.  Somewhere in the target description we
associate a9 with -mattr=+thumb2.

There are plenty of other ways to get the same result, and it's all very
confusing and opaque. Don't ask me what triples are valid. I usually verify
that I have the right command line by staring at the disassembly until I'm
convinced.

One good thing about llc (unlike other drivers... *cough*) is that the option
values are actually discoverable!

llc --version gives you -march= values.
llc -mcpu=help
llc -mattr=help

-Andy
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