Interpolation (insert string directly) VS concatenation in the performance aspect

Question

Which is below method is faster when combining 2 strings ? And why can it run faster?

PHP code:

$str1 = 'Hello';
$str2 = 'World';

method 1:

$txt = $str1.$str2;

method 2:

$txt = "$str1$str2";

possible duplicate of [Speed difference in using inline strings vs concatenation in php5?](http://stackoverflow.com/questions/13620/speed-difference-in-using-inline-strings-vs-concatenation-in-php5) — Michael Berkowski, Nov 25 '12 at 22:10

Ja͢ck · Answer 1 · 2012-11-26T10:04:43.180

5

Opcode comparison

Code:

$a=1; 
$b=2; 
echo "$a$b";

Opcodes:

   1     0  >   ASSIGN                                                   !0, 1
         1      ASSIGN                                                   !1, 2
         2      ADD_VAR                                          ~2      !0
         3      ADD_VAR                                          ~2      ~2, !1
         4      ECHO                                                     ~2
         5    > RETURN                                                   null

Code:

$a=1; 
$b=2; 
echo $a.$b;

Opcodes:

   1     0  >   ASSIGN                                                   !0, 1
         1      ASSIGN                                                   !1, 2
         2      CONCAT                                           ~2      !0, !1
         3      ECHO                                                     ~2
         4    > RETURN                                                   null

Intermediate conclusion

Concatenation has one less opcode, rejoice! Not really, we still have to test the actual runtime performance.

To see the opcodes generated by any piece of code, have a look at the great vld extension

Runtime performance

Ran over 0.5m iterations on a workstation (average over 10 runs):

Inlined: 0.9793s
Concatenated: 0.9252s

Conclusion

Concatenation is faster, though it's unlikely to impact the performance of any particular application.

edited Nov 26 '12 at 10:04

answered Nov 25 '12 at 17:26

Ja͢ck

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1

How do you know one `CONCAT` is faster than two `ADD_VAR`s? – Gumbo Nov 25 '12 at 17:27
1

Where can I get such a print of the opcodes? – Madara's Ghost Nov 25 '12 at 17:31
1

@MadaraUchiha [`vld`](http://pecl.php.net/vld) – Ja͢ck Nov 25 '12 at 17:34
@Gumbo substantiated with runtime performance test. – Ja͢ck Nov 25 '12 at 17:34
What version of php did you use ? – Baba Nov 25 '12 at 18:01
I meant what version of `vld` just noticed that `EXT_STMT` was not captured in your output or you just filtered the essential parts – Baba Nov 25 '12 at 18:09
@Baba Oh, it's 0.11.2; what's `EXT_STMT` supposed to do? – Ja͢ck Nov 25 '12 at 18:16
@Jack: You can not compare opcodes and then think less is faster. Johannes Schlüter explained that in one presentation better than I could do, I suggest to take some looks around if you are concerned about internals. – hakre Nov 26 '12 at 09:36
@hakre Perhaps the first sentence under 'Intermediate conclusion' was not phrased properly, but the answer covers both opcode analysis and runtime performance. – Ja͢ck Nov 26 '12 at 10:03

Interpolation (insert string directly) VS concatenation in the performance aspect

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