[Valgrind-developers] redundant code in vg_dispatch.S?

[Nicholas N. <nj...@ca...>]

Hi,

vg_dispatch.S has this code:

---------------------------
        /* Set up the baseBlock pointer */
        movl    $VG_(baseBlock), %ebp

        /* fetch m_eip into %eax */
        movl    VGOFF_(m_eip), %esi
        movl    (%ebp, %esi, 4), %eax

dispatch_main:
        /* Jump here to do a new dispatch.
           %eax holds destination (original) address.
           %ebp indicates further details of the control transfer
           requested to the address in %eax.

           If ebp == & VG_(baseBlock), just jump next to %eax.

           If ebp == VG_EBP_JMP_SYSCALL, do a system call before
           continuing at eax.

           If ebp == VG_EBP_JMP_CLIENTREQ, do a client request before
           continuing at eax.

           If %ebp has any other value, we panic.
        */
        cmpl    $VG_(baseBlock), %ebp
        jnz     dispatch_exceptional
        /* fall into main loop */

dispatch_boring:
        /* save the jump address at VG_(baseBlock)[VGOFF_(m_eip)] */
        movl    VGOFF_(m_eip), %esi
        movl    %eax, (%ebp, %esi, 4)
---------------------------

AFAICT, the entire bit between dispatch_main: and dispatch_boring: can be
removed -- the cmpl and the jnz never occur, because we've just loaded
%ebp with $VG_(baseBlock).  I've tried it, it works fine.  Maybe the
comment should be moved elsewhere, I'm not sure.  I don't think it will
affect performance much, because it's outside the main loop, but still...

N