This is performance regression from 4.3 (which was better).
On i386, when -O2 -fomit-frame-pointer -mpreferred-stack-boundary=2 is used,
and function operates with long long values, stack frame is generated, although
it doesn't have to be.
Example:
int f(long long x);
int g(long long x)
{
f(x);
return 0;
}
Generated code:
.text
.p2align 4,,15
.globl g
.type g, @function
g:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
movl 8(%ebp), %eax
movl 12(%ebp), %edx
movl %eax, (%esp)
movl %edx, 4(%esp)
call f
xorl %eax, %eax
leave
ret
.size g, .-g
Gcc 4.3 didn't generate stack frame in this case. On i386, spurious stack frame
is especially bad because there are few registers and one register is lost for
the stack frame. One my program doing heavy 64-bit math shows almost 1% code
size increase because of these unneeded frames.
--
Summary: Performance regression: stack frames are generated even
with -fomit-frame-pointer
Product: gcc
Version: 4.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: regression
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: mikulas at artax dot karlin dot mff dot cuni dot cz
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40667
