https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92807
Sunil Pandey <skpgkp2 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |hjl.tools at gmail dot com,
| |skpgkp2 at gmail dot com
Summary|gcc generate extra move for |gcc generate extra move for
|the snippet code |the snippet code along with
| |lea instruction.
--- Comment #1 from Sunil Pandey <skpgkp2 at gmail dot com> ---
$ cat t1.c
#include<stdint.h>
uint32_t abs2( uint32_t a )
{
uint32_t s = ((a>>15)&0x10001)*0xffff;
return (a+s)^s;
}
$ gcc --version
gcc (GCC) 9.2.1 20190827 (Red Hat 9.2.1-1)
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ gcc -Ofast -S t1.c -o t1.s.gcc.9
$ cat t1.s.gcc.9
.file "t1.c"
.text
.p2align 4
.globl abs2
.type abs2, @function
abs2:
.LFB0:
.cfi_startproc
movl %edi, %edx
shrl $15, %edx
andl $65537, %edx
movl %edx, %eax
sall $16, %eax
subl %edx, %eax
movl %eax, %edx
leal (%rdi,%rax), %eax
xorl %edx, %eax
ret
.cfi_endproc
.LFE0:
.size abs2, .-abs2
.ident "GCC: (GNU) 9.2.1 20190827 (Red Hat 9.2.1-1)"
.section .note.GNU-stack,"",@progbits
Intel compiler generate add instead of lea as well as 1 less mov instruction
for same code.
$ icc -Ofast -S t1.c -o t1.s.icc
$ cat t1.s.icc
.L_2__routine_start_abs2_0:
# -- Begin abs2
.text
# mark_begin;
.align 16,0x90
.globl abs2
# --- abs2(uint32_t)
abs2:
# parameter 1: %edi
..B1.1: # Preds ..B1.0
# Execution count [1.00e+00]
.cfi_startproc
..___tag_value_abs2.1:
..L2:
#3.1
movl %edi, %edx #4.23
shrl $15, %edx #4.23
andl $65537, %edx #4.27
movl %edx, %eax #4.36
shll $16, %eax #4.36
subl %edx, %eax #4.36
addl %eax, %edi #5.19
xorl %edi, %eax #5.22
ret #5.22
.align 16,0x90
# LOE
.cfi_endproc
# mark_end;
.type abs2,@function
.size abs2,.-abs2
..LNabs2.0:
.data
# -- End abs2
.data
.section .note.GNU-stack, ""
# End
