Re: committed [RISC-V]: Harden test scan patterns

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/27/23 12:22, Joern Rennecke wrote:
> On Wed, 27 Sept 2023 at 18:22, Jeff Law <jeffreyalaw@gmail.com> wrote:
> 
>> It would help to describe how these patterns were under specified so
>> that folks don't continue to make the same mistake as new tests get added.
> 
> dg-final scan-assembler, scan-assembler-not, and scan-assembler-times
> use a tcl regular expression (often referred to abbreviated as RE), as
> described in https://www.tcl.tk/man/tcl8.4/TclCmd/re_syntax.html .
> 
> If your RE is not specific enough, it can match LTO information that the
> compiler places into its assembly output when the relevant options are
> provided, which is common when running tests where the test harness
> iterates over a number of optimization option combinations.
> Note that '.' is an atom that can match any character.  If you want to
> match a dot specifically, you have to escape it with a backslash: '\.' .
> When you are matching an instruction mnemonic, an effective way to
> avoid matching in LTO information is to enforce matching of word start
> (\m) and/or word end (\M) .
> Note also that the backslash has to be quoted.  If the RE is enclosed in
> '"' quotes, extra backslashes are needed.  That is not necessary when it
> is enclosed in curly braces.
> 
> For example, "ld.w" will be matched in:
> 
> .ascii  "h\227\022\212ld@w\251jr\254'\320\255vwj\252\026\016\364"
> 
> If you write {\mld\.w\M} instead, you avoid this problem.
OK.  So that naturally leads to the question, why aren't others seeing 
this, both in the RISC-V world and more generally.  I'm not aware of any 
case where I've run the testsuite and tripped over this issue, nor am I 
aware of anyone else tripping over it.

Jeff