Consider:
foo(int *x)
{
*x = 0;
}
Compile with -Os -fomit-frame-pointer and you'll get something like this:
movl 4(%esp), %eax
movl $0, (%eax)
It would be 2 bytes shorter to instead load the constant 0 via an xor
instruction into a scratch register, then store the scratch register into the
memory location. Something like this:
movl 4(%esp), %eax
xor %edx, %edx
movl %edx, (%eax)
ISTM this could easily be implemented with a peep2.
I'm not well versed enough in x86 instruction timings to know if the xor
sequence is going to generally be faster.
--
Summary: GCC choosing poor code sequence for certain stores (x86)
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: law at redhat dot com
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=41505
