Re: optimization/7247: copy constructor missing when inlining enabled for i386

[Jason Merrill <jason@redhat.com>]

The following reply was made to PR optimization/7247; it has been noted by GNATS.

From: Jason Merrill <jason@redhat.com>
To: "H. J. Lu" <hjl@lucon.org>
Cc: gawrilow@math.tu-berlin.de, gcc-gnats@gcc.gnu.org,
	gcc-bugs@gcc.gnu.org
Subject: Re: optimization/7247: copy constructor missing when inlining
 enabled for i386
Date: Thu, 11 Jul 2002 22:02:12 +0100

 >>>>> "H" == H J Lu <hjl@lucon.org> writes:
 
 > Jason, it looks like your patch doesn't catch this one.
 
 No, as the bug isn't related to the NRVO; this testcase doesn't have any
 returns which would be affected.  Rather, it seems to be a dependency
 tracking bug.  I can reproduce the bug by adding 'inline' to the definition
 of incidence_matrix and compiling with -O -fschedule-insns2.  Without
 -fschedule-insns2, the code leading up to the dump_op calls looks like
 
         movl    -96(%ebp), %eax
         movl    -92(%ebp), %edx
         movl    %eax, -52(%ebp)
         movl    %edx, -48(%ebp)
         leal    -96(%ebp), %eax
         movl    %eax, (%esp)
         call    pm::dump_op(pm::double_zero const&)
         leal    -52(%ebp), %eax
         movl    %eax, (%esp)
         call    pm::dump_op(pm::double_zero const&)
 
 so the epsilon value is properly copied before it is dumped.  But with
 scheduling, it looks like
 
         movl    -96(%ebp), %eax
         movl    %eax, -52(%ebp)
         leal    -96(%ebp), %eax
         movl    %eax, (%esp)
         call    pm::dump_op(pm::double_zero const&)
         leal    -52(%ebp), %eax
         movl    %eax, (%esp)
         call    pm::dump_op(pm::double_zero const&)
 
 Which suggests that the scheduler incorrectly decides that the second word
 wasn't used by the call and optimizes away the copy.  This bug, or a
 similar one, seems still to be present in the trunk, though to see it you
 also need to move the definition of the double_zero constructor outside the
 class, so it is not inlined.
 
 Jason