Re: Serious structure return code-size/speed regression with SRA

[Mark Mitchell <mark at codesourcery dot com>]

Jakub Jelinek wrote:

> Hi!
>
> struct A { int a : 1, b : 1, c : 1, d : 1, e : 1, f : 1, g : 1, h : 1,
>               i : 1, j : 1, k : 1, l : 1, m : 1, n : 1, o : 1, p : 1,
>               q : 2, r : 2, s : 2, t : 2, u : 2, v : 2, w : 2, x : 2; };
> struct A foo (struct A x)
> {
>  return x;
> }
> struct A a, b;
> struct A bar (void)
> {
>  return a;
> }
> void baz (void)
> {
>  a = b;
> }
> void test (struct A x)
> {
>  a = x;
> }
>
> On say x86-64, foo is 529 bytes long (without padding) on HEAD at -O2,
> while only 3 bytes long (2 insns) in 3.4.1.  Similarly the test function.
> bar and baz are the same size/speed as in 3.4.1.
> The problem is that assignment of the struct argument is in SRA split up
> into a series of field assignments, which is definitely way worse in this
> case.
I think you should file a PR, mark it as a regression, target it at 
3.5.0, and assign it to Richard Henderson, who will no doubt fix it with 
his usual efficacy.

--
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com