optimization/9566: Inline function produces much worse code than manual inlining.

[Andrew Pinski]

The following reply was made to PR optimization/9566; it has been noted by GNATS.

From: Andrew Pinski <pinskia@physics.uc.edu>
To: Andrew Pinski <pinskia@physics.uc.edu>
Cc: gcc-gnats@gcc.gnu.org, osv@javad.ru, gcc-bugs@gcc.gnu.org,
   nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org
Subject: Re: optimization/9566: Inline function produces much worse code than manual inlining.
Date: Mon, 14 Apr 2003 20:12:39 -0400

 Actually it is because C++'s this is pointer, so it spills the struct 
 the stack because of it.
 This g3 is the same as g1. Sorry about the pervious message, I did not 
 look at it too much.
 
 struct A {
    char const* src;
    char* dest;
    void copy() { *++dest = *++src; }
 };
 
 void g1() {
    A a;
    for(int i = 0; i < 10; ++i)
      a.copy();
 }
 void g3() {
    A a;
    for(int i = 0; i < 10; ++i)
    {
      A *b = &a;
      *++b->dest = *++b->src;
    }
 }
 
 A way to fix if the pointer to a local variable is only used for 
 load/store and not used for passing into a function or the pointer does 
 not change, is to remove the pointer and change it to what the pointer 
 points to (this might only be able to do on the ssa-branch).
 
 (As a side, it is still bad also on the ssa-branch from `3.5-tree-ssa 
 20030117`.)
 
 Thanks,
 Andrew Pinski