Emit EXT_STMT for each 'elseif' clause

[derickr]

This tiny change emits an extra EXT_STMT opcode for each elseif child in an AST_IF list.

The reason why I am proposing this, is as follows:

A user reported a bug #2095 with Xdebug's code coverage, which complains that lines with elseif on them do not get "counted" as being it, where else if lines do.

The generated opcodes are for the elseif version:

   12     0  E >   EXT_STMT                                                 
          1        ASSIGN                                                   !0, 'bar'
   13     2        EXT_STMT                                                 
          3      > JMPZ                                                     <false>, ->7
   14     4    >   EXT_STMT                                                 
          5        ECHO                                                     'hello+1'
          6      > JMP                                                      ->11
   15     7    >   IN_ARRAY                                                 !0, <array>
          8      > JMPZ                                                     ~2, ->11
   16     9    >   EXT_STMT                                                 
         10        ECHO                                                     'hello+2'
   18    11    >   EXT_STMT                                                 
         12      > RETURN                                                   null

And for the else if version:

    3     0  E >   EXT_STMT                                                 
          1        ASSIGN                                                   !0, 'bar'
    4     2        EXT_STMT                                                 
          3      > JMPZ                                                     <false>, ->7
    5     4    >   EXT_STMT                                                 
          5        ECHO                                                     'hello+1'
          6      > JMP                                                      ->12
    6     7    >   EXT_STMT                                                 
          8        IN_ARRAY                                                 !0, <array>
          9      > JMPZ                                                     ~2, ->12
    7    10    >   EXT_STMT                                                 
         11        ECHO                                                     'hello+2'
    9    12    >   EXT_STMT                                                 
         13      > RETURN                                                   null

In the elseif variant, the EXT_STMT (opcode 7) is indeed missing.

Xdebug uses this opcode for both code coverage analysis, as well as single stepping. The step debugger would also not have stopped at the elseif line.

The reason here is that with else if it is really seen as two different things, with the if being a new statement (and hence creating its own EXT_STMT), where with elseif it is a continuation of the original if, which does not emit an EXT_STMT for each separate condition. This patch equalizes the behaviour.

[cmb69]

Can we reasonably be sure that this additional OPcode won't cause issues with other zend_extensions which have a statement_handler? Otherwise it would be better to target master only.

[derickr]

@cmb69 I am not aware of any open source Zend extensions, so I can't check to make sure. However, I'm confident that it will not cause issues, as it would also rather just fix bugs for these. Opcache doesn't use the handler, either.

[derickr]

Other examples of where it isn't used:

• https://github.com/krakjoe/autostrict/blob/d3970ae147523ce2b519c70bcb3141e8d11a3205/auto.c#L104
• https://github.com/DataDog/dd-prof-php/blob/f33647fc15df64b66ff525a40cefcc520b9266b9/datadog-profiling.c#L19
• https://github.com/nbs-system/snuffleupagus/blob/c5d249119375c95fdcdf4124b330c918fb03f4b5/src/snuffleupagus.c#L70
• https://github.com/krakjoe/dbc/blob/30c35466050ba68d7e5c1b0ad491950c6e72c534/dbc.c#L342
• https://github.com/zhuowei/afl-php/blob/43b553c4d17b2238a8f45997dc82ab5ce6dbe647/zend_extension/aflphp.c#L49
• https://github.com/scoutapp/scout-apm-php-ext/blob/1a5df8f8ffee756d712c92646c20b75196ef23d8/zend_scoutapm.c#L111
• https://github.com/mit-scripts/scripts/blob/40aaee344bce6a96603ece7fc26f58c4f4b7f954/server/common/oursrc/php_scripts/php_scripts.c#L75
• https://github.com/krakjoe/cloname/blob/871b3922edefd82731ef97cec5078c317079ad13/zend_cloname.c#L40
• https://github.com/krakjoe/stat/blob/eff23e7ce505920856290d80801f89519883c584/zend_stat.c#L72