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

[James Henderson via llvm-dev]

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
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