From ba5248fcde21acfb9d93220ec07256804525c18e Mon Sep 17 00:00:00 2001 From: Daniel Dragan Date: Wed, 4 Jun 2014 23:17:39 -0400 Subject: remove 1 read of interp var from PUSHMARK PL_markstack_ptr was read once to do the ++ and comparison. Then after the markstack_grow call, or not, depending on the branch. The code reads PL_markstack_ptr a 2nd time. It has to be reread in case (or always does) markstack_grow reallocs the mark stack. markstack_grow has a void retval. That is a waste of a register. Let us put it to use to return the new PL_markstack_ptr. In markstack_grow the contents that will be assigned to PL_markstack_ptr are already in a register. So let the I32* flow out from markstack_grow to its caller. In VC2003 32 bit asm, mark_stack_entry is register eax. The retval of markstack_grow is in eax. So the assignment "=" in "mark_stack_entry = markstack_grow();" has no overhead. Since the other, not extend branch, is function call free, "(mark_stack_entry = ++PL_markstack_ptr)" assigns to eax. Ultimatly with this patch a 3 byte mov instruction is saved for each instance of PUSHMARK, and 1 interp var read is removed. I observed 42 callers of markstack_grow with my disassembler, so theoretically 3*42 bytes of machine code was removed for me. Perl_pp_pushmark dropped from 0x2b to 0x28 bytes of x86 VC 2003 machine code. [perl #122034] --- pp.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'pp.h') diff --git a/pp.h b/pp.h index 3623a38f0f..a7e936ccaf 100644 --- a/pp.h +++ b/pp.h @@ -57,9 +57,10 @@ Refetch the stack pointer. Used after a callback. See L. #define PUSHMARK(p) \ STMT_START { \ - if (UNLIKELY(++PL_markstack_ptr == PL_markstack_max)) \ - markstack_grow(); \ - *PL_markstack_ptr = (I32)((p) - PL_stack_base);\ + I32 * mark_stack_entry; \ + if (UNLIKELY((mark_stack_entry = ++PL_markstack_ptr) == PL_markstack_max)) \ + mark_stack_entry = markstack_grow(); \ + *mark_stack_entry = (I32)((p) - PL_stack_base); \ } STMT_END #define TOPMARK (*PL_markstack_ptr) -- cgit v1.2.1