https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102169
Carl Love <carll at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |carll at gcc dot gnu.org
--- Comment #5 from Carl Love <carll at gcc dot gnu.org> ---
With no optimization, GCC generates a three instruction sequence to store to
the stack frame rather than using a single stw instruction.
Adding this for informational purposes per Segher's request.
The test program
#include <stdio.h>
#include <stdlib.h>
int marker2 (int a) { return (1); }
int
main (int argc, char **argv, char **envp)
{
marker2 (43);
return argc;
}
Generates the three instruction sequence in both the main and marker2 function.
Just cutting and pasting the marker2 code for P9 and P10.
On Power 9
carll@marlin:~$ gcc -g stfiwx-bug.c -o stfiwx-bug
carll@marlin:~$ objdump -S -d stfiwx-bug > stfiwx-bug.dump
carll@marlin:~$ which gcc
/usr/bin/gcc
carll@marlin:~$ gcc --version
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
int marker2 (int a) { return (1); }
7bc: f8 ff e1 fb std r31,-8(r1)
7c0: c1 ff 21 f8 stdu r1,-64(r1)
7c4: 78 0b 3f 7c mr r31,r1
7c8: 78 1b 69 7c mr r9,r3
7cc: 2c 00 3f 91 stw r9,44(r31) << here
7d0: 01 00 20 39 li r9,1
7d4: 78 4b 23 7d mr r3,r9
7d8: 40 00 3f 38 addi r1,r31,64
7dc: f8 ff e1 eb ld r31,-8(r1)
7e0: 20 00 80 4e blr
on Power 10
carll@ltcd97-lp1:~$ gcc -g stfiwx-bug.c -o stfiwx-bug
carll@ltcd97-lp1:~$ objdump -S -d stfiwx-bug > stfiwx-bug.dump
carll@ltcd97-lp1:~$ which gcc
/usr/bin/gcc
carll@ltcd97-lp1:~$ gcc --version
gcc (Ubuntu 10.3.0-1ubuntu1) 10.3.0
int marker2 (int a) { return (1); }
7bc: f8 ff e1 fb std r31,-8(r1)
7c0: c1 ff 21 f8 stdu r1,-64(r1)
7c4: 78 0b 3f 7c mr r31,r1
7c8: 78 1b 69 7c mr r9,r3
7cc: e6 01 09 7c mtfprwz f0,r9 << here
7d0: 2c 00 3f 39 addi r9,r31,44 << here
7d4: ae 4f 00 7c stfiwx f0,0,r9 << here
7d8: 01 00 20 39 li r9,1
7dc: 78 4b 23 7d mr r3,r9
7e0: 40 00 3f 38 addi r1,r31,64
7e4: f8 ff e1 eb ld r31,-8(r1)
7e8: 20 00 80 4e blr
