do-while is the fastest loop in php?

  1. Micro optimizations are evil. They reduce readability for no measurable performance gain. Even if your application does have loops with millions of iterators (which I doubt) the difference is still negligible.
  2. The difference between while / do while is smaller than you say: http://codepad.viper-7.com/M8cgt9

  3. To understand why do while is marginally faster, look at the generated opcodes:

    line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
# while loop
   3     0  >   ASSIGN                                                   !0, 0
   4     1  >   IS_SMALLER                                       ~1      !0, 1000000
         2    > JMPZ                                                     ~1, ->5
         3  >   PRE_INC                                                  !0
         4    > JMP                                                      ->1
         5  > > RETURN                                                   1
# do while loop
   3     0  >   ASSIGN                                                   !0, 0
   4     1  >   PRE_INC                                                  !0
         2      IS_SMALLER                                       ~2      !0, 1000000
         3    > JMPNZ                                                    ~2, ->1
   4        > > RETURN                                                   1
# for loop
   3     0  >   ASSIGN                                                   !0, 0
         1  >   IS_SMALLER                                       ~1      !0, 1000000
         2    > JMPZNZ                                        5          ~1, ->6
         3  >   PRE_INC                                                  !0
         4    > JMP                                                      ->1
         5  > > JMP                                                      ->3
         6  > > RETURN                                                   1

    The do while loop only has one jump statement (JMPNZ), whereas the while loop needs two (JMPZ, JMP). The for loop needs three jump statements (JMPZNZ, JMP, JMP) and has generally more complex logic.

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Performance

Php

Do While

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