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

[Vineet Gupta <vineetg@rivosinc.com>]

On 9/27/23 13:14, Jeff Law 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.

Actually I did run into it. See commit ecfa870ff29d979bd2c ("RISC-V: 
optim const DF +0.0 store to mem [PR/110748]") where a false failure was 
triggered due to these random LTO strings and needed adjusting.

-/* { dg-final { scan-assembler-not "sw" } } */
-/* { dg-final { scan-assembler-not "fld" } } */
-/* { dg-final { scan-assembler-not "fsd" } } */
-/* { dg-final { scan-assembler-not "lw" } } */
+/* { dg-final { scan-assembler-not "\tsw\t" } } */
+/* { dg-final { scan-assembler-not "\tfld\t" } } */
+/* { dg-final { scan-assembler-not "\tfsd\t" } } */
+/* { dg-final { scan-assembler-not "\tlw\t" } } */