llvm dev - Jun 2012 - [LLVMdev] Big endian ARM?

On Jun 2, 2012, at 8:35 PM, Richard Pennington wrote:
>> i.e. the test of the value is optimized to use a byte load, but the
ldrb is
>> done assuming a little endian address space.
>> 
>> I've been snooping around, but can't seem to find where the
conversion to a
>> byte operation is done. Could someone point me in the right direction?
>> 
> 
> I've figured out my problem. I didn't adjust the data layout
description string
> in ARMTargetMachine.cpp for big endian targets.
> 
> This brings up another question. clang has its own set of description
strings
> for varying ABIs, etc. Should those strings somehow override in the code 
> generators?
The current design is that the frontend (if it attaches a TD string) is
*required* to match the code generator:
http://llvm.org/docs/LangRef.html#datalayout

It is intended to allow the mid-level optimizers to know about data layout
without having the code generator linked in (e.g. "opt").

-Chris

On Sun, 03 Jun 2012 11:39:21 -0700
Chris Lattner <clattner at apple.com> wrote:
> On Jun 2, 2012, at 8:35 PM, Richard Pennington wrote:
> >> i.e. the test of the value is optimized to use a byte load, but
> >> the ldrb is done assuming a little endian address space.
> >> 
> >> I've been snooping around, but can't seem to find where
the
> >> conversion to a byte operation is done. Could someone point me in
> >> the right direction?
> >> 
> > 
> > I've figured out my problem. I didn't adjust the data layout
> > description string in ARMTargetMachine.cpp for big endian targets.
> > 
> > This brings up another question. clang has its own set of
> > description strings for varying ABIs, etc. Should those strings
> > somehow override in the code generators?
> 
> The current design is that the frontend (if it attaches a TD string)
> is *required* to match the code generator:
> http://llvm.org/docs/LangRef.html#datalayout
Chris,

Do we actually verify this anywhere?

 -Hal
> 
> It is intended to allow the mid-level optimizers to know about data
> layout without having the code generator linked in (e.g. "opt").
> 
> -Chris
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-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory

>> The current design is that the frontend (if it attaches a TD string)
>> is *required* to match the code generator:
>> http://llvm.org/docs/LangRef.html#datalayout
>
> Chris,
>
> Do we actually verify this anywhere?
No.  This has been on my todo list for a long time - people regularly get bitten
by it.

Ciao, Duncan.