Op 2019-07-02 om 19:41 schreef Ryan Joseph:
On Jul 2, 2019, at 10:32 AM, Michael Van Canneyt <mich...@freepascal.org> wrote:
It overwrites the first. There is no such thing as '2 VMT tables'.
That’s what I thought. How costly is this? Not sure what it’s doing under the
hood but I’d like to know more.
You'd expect a mov of a constant to a memory location, but it is a bit
more involved, and it doesn't look very optimal. Maybe because it is
compiler generated, the optimizer doesn't run over it? (this is -O4 code)
P$PROGRAM$_$TA_$__$$_CREATE$$LONGBOOL:
# [13] begin
pushl %ebp
movl %esp,%ebp
leal -8(%esp),%esp //
creates stackspace
# Var $vmt located at ebp-4, size=OS_32
# Var $self located at ebp-8, size=OS_32
movl %eax,-8(%ebp)
movl %edx,-4(%ebp)
leal -4(%ebp),%edx // self,
movl -8(%ebp),%eax
movl $0,%ecx
call fpc_help_constructor
movl %eax,-8(%ebp) // save result
on stack.
testl %eax,%eax
.Lj26:
.Lj15:
# [14] end;
movl -8(%ebp),%eax // and reload
that result. All instructions after call are no effective purpose.
leave
ret
movl $VMT_$P$PROGRAM_$$_TA,%edx
movl $U_$P$PROGRAM_$$_OBJ,%eax
call P$PROGRAM$_$TA_$__$$_CREATE$$LONGBOOL // tried to inline
ta.create, not accepted.
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