[llvm-dev] Syntax for FileCheck numeric variables and expressions

[via llvm-dev]

> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
> Thomas Preudhomme via llvm-dev
> Sent: Monday, July 16, 2018 6:24 AM
> To: jh7370.2008 at my.bristol.ac.uk
> Cc: llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] Syntax for FileCheck numeric variables and
> expressions
> 
> Hi James,
> 
> I like that suggestion very much but I think keeping the order of the
> two sides as initially proposed makes more sense. In printf/scanf the
> string is first because the primary use of these functions is to do
> I/O and so you first specify what you are going to output/input and
> then where to capture variables. The primary objective of FileCheck
> variables and expressions is to capture/print them, the specifier is
> an addon to allow some conversion. Does it make sense?

My immediate reaction is that I'd rather not have FileCheck get into
the business of handling printf specifiers.  OTOH, while LLVM tools
do typically print lowercase hex, that's not guaranteed, and looking
at the output of other tools can be useful too.  So, a way to specify
the case for a hex conversion seems worthwhile.

I had also been thinking in terms of the trailing colon to distinguish
definition from use, as James suggested, that's sort-of consistent 
with the current syntax.

This is starting to make parsing the insides of [[]] much more involved,
so you'll want to pay attention to making that code well-structured and
readable.
--paulr

> 
> In the interest of speeding things up I plan to start implementing
> this proposal starting tomorrow unless someone gives some more
> feedback.
> 
> Best regards,
> 
> Thomas
> 
> On Fri, 13 Jul 2018 at 15:51, James Henderson
> <jh7370.2008 at my.bristol.ac.uk> wrote:
> >
> > Hi Thomas,
> >
> > In general, I think this is a good proposal. However, I don't think that
> using ">" or "<" to specify base (at least alone) is a good idea, as it
> might clash with future ideas to do comparisons etc. I also think it would
> be nice to have the syntax consistent between definition and use. My first
> thought on a reasonable alternative was to use commas to separate the two
> parts, so something like:
> >
> > [[# VAR, 16:]] to capture a hexadecimal number (where the spaces are
> optional). [[# VAR, 16]] to use a variable, converted to a hexadecimal
> string. In both cases, the base component is optional, and defaults to
> decimal.
> >
> > This led me to thing that it might be better to use something similar to
> printf style for the latter half, so to capture a hexadecimal number with
> a leading "0x" would be: "0x[[# VAR, %x:]]" and to use it would be "0x[[#
> VAR, %x]]". Indeed, that would allow straightforward conversions between
> formats, so say you defined it by capturing a decimal integer and using it
> to match a hexadecimal in upper case, with leading 0x and 8 digits
> following the 0x:
> >
> > CHECK: [[# VAR, %d:]] # Defines
> > CHECK: 0x[[# VAR + 1, %8X]] # Uses
> >
> > Of course, if we go down that route, it would probably make more sense
> to reverse the two sides (e.g. to become "[[# %d, VAR:]]" to capture a
> decimal and "[[# %8X, VAR + 1]]" to use it).
> >
> > Regards,
> >
> > James
> >
> > On 12 July 2018 at 15:34, Thomas Preudhomme via llvm-dev <llvm-
> dev at lists.llvm.org> wrote:
> >>
> >> Hi all,
> >>
> >> I've written a patch to extend FileCheck to support matching
> >> arithmetic expressions involving variable [1] (eg. to match REG+1
> >> where REG is a variable with a numeric value). It was suggested to me
> >> in the review to introduce the concept of numeric variable and to
> >> allow for specifying the base the value are written in.
> >>
> >> [1] https://reviews.llvm.org/D49084
> >>
> >> I think the syntax should satisfy the below requirements:
> >>
> >> * based off the [[]] construct since anything else might overload an
> >> existing valid syntax (eg. $$ is supposed to match literally now)
> >> * consistent with syntax for expressions using @LINE
> >> * consistent with using ':' to define regular variable
> >> * allows to specify base of the number a numeric variable is being set
> to
> >> * allows to specify base of the result of the numeric expression
> >>
> >> I've come up with the following syntax for which I'd like feedback:
> >>
> >> Numeric variable definition: [[#X<base:]] (eg. [[#ADDR<16:]]) where X
> >> is the numeric variable being defined and <base is optional in which
> >> case base defaults to 10
> >> Numeric variable use: [[#X>base]] (eg. [[#ADDR]]>2) where <base is
> >> optional in which case base defaults 10
> >> Numeric expression: [[exp>base]] (eg. [[#ADDR+2>16]] where expression
> >> must contain at least one numeric variable
> >>
> >>
> >> I'm not a big fan of the > for the output base being inside the
> >> expression but [[exp]]>base would match >base literally.
> >>
> >> Any suggestions / opinions?
> >>
> >> Best regards,
> >>
> >> Thomas
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> >
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