llvm dev - Dec 2012 - [LLVMdev] Getting rid of tabs in LLVM's assembly output?

On Tue, Dec 18, 2012 at 3:36 PM, Tim Northover <t.p.northover at
gmail.com>wrote:
> > > Maybe it's naive, but I would expect it to be easy for each
backend to
> > > expose a constant N which is the length of the longest mnemonic,
and
> then
> > > for the printer to pad to N+1 or N+2….
> >
> > That would probably work for X86, but other targets (ARM in
particular)
> > often have operands which are printed/parsed as suffices on the
mnemonic
> > itself.  Because of these, the backend does not statically know the
> longest
> > potential string-of-stuff-before-the-tab.
>
> Are you thinking of something beyond the ".F32.I16" suffixes (for
> example)? If not, the result may not be TableGeneratable, but is
> probably conservatively known as "8 + natural mnemonic length"
for
> these purposes.
>
The great thing is, if its close enough, it doesn't matter if there exist
corner cases that are formatted less well.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20121218/cee8616c/attachment.html>

On Dec 18, 2012, at 3:39 PM, Chandler Carruth <chandlerc at google.com>
wrote:
> On Tue, Dec 18, 2012 at 3:36 PM, Tim Northover <t.p.northover at
gmail.com> wrote:
> > > Maybe it's naive, but I would expect it to be easy for each
backend to
> > > expose a constant N which is the length of the longest mnemonic,
and then
> > > for the printer to pad to N+1 or N+2….
> >
> > That would probably work for X86, but other targets (ARM in
particular)
> > often have operands which are printed/parsed as suffices on the
mnemonic
> > itself.  Because of these, the backend does not statically know the
longest
> > potential string-of-stuff-before-the-tab.
> 
> Are you thinking of something beyond the ".F32.I16" suffixes (for
> example)? If not, the result may not be TableGeneratable, but is
> probably conservatively known as "8 + natural mnemonic length"
for
> these purposes.
> 
> The great thing is, if its close enough, it doesn't matter if there
exist corner cases that are formatted less well.
It affects pretty much all ARM instructions, which can have a predicate suffix. 
Some can also have an S suffix.  Those are not expressed to tblgen as part of
the mnemonic, so it can't know about them when computing a maximum mnemonic
length.

--Owen
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20121218/319efc31/attachment.html>

> It affects pretty much all ARM instructions, which can have a predicate
That suggests to me that a Target callback may be the way to go rather than
relying on TableGen getting the right answer. Realistically '\t'
doesn't
get it right every time at the moment. Even ignoring long instructions
(which exist), InstAliases only work with a single space.

Make it a well-documented pure-virtual method in the appropriate class and
implementors will be even more more likely to see it.

Tim.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20121218/a10c1897/attachment.html>