The abstract syntax tree of two codes can be compared to verify that their differences are only cosmetic (such as free vs. fixed source form). The intermediate and assembly codes of different source codes and optimization levels can be compared to understand speed differences.
module fib_mod
implicit none
contains
elemental function fib(i) result(ifib)
integer, intent(in) :: i
integer :: ifib,j,fib_old(2)
ifib = merge(0, 1, i<1)
if (i < 3) return
fib_old = [1,1]
do j=3,i
ifib = fib_old(1) + fib_old(2)
if (j == i) exit
fib_old = [ifib,fib_old(1)]
end do
end function fib
end module fib_mod
!
program test_fib
use fib_mod, only: fib
implicit none
print*,"fib(6) =",fib(6) ! 8
end program test_fibNamespace: A-Z: (UNKNOWN 0)
procedure name = fib_mod
symtree: 'fib' || symbol: 'fib'
type spec : (INTEGER 4)
attributes: (PROCEDURE MODULE-PROC FUNCTION ELEMENTAL PURE CONTAINED ALWAYS-EXPLICIT)
result: ifib
Formal arglist: i
symtree: 'fib_mod' || symbol: 'fib_mod'
type spec : (UNKNOWN 0)
attributes: (MODULE )
code:
CONTAINS
Namespace: A-Z: (UNKNOWN 0)
procedure name = fib
symtree: 'fib' || symbol: 'fib' from namespace 'fib_mod'
symtree: 'fib_old' || symbol: 'fib_old'
type spec : (INTEGER 4)
attributes: (VARIABLE DIMENSION)
Array spec:(1 [0] AS_EXPLICIT 1 2 )
symtree: 'i' || symbol: 'i'
type spec : (INTEGER 4)
attributes: (VARIABLE DUMMY(IN))
symtree: 'ifib' || symbol: 'ifib'
type spec : (INTEGER 4)
attributes: (VARIABLE RESULT ALWAYS-EXPLICIT)
symtree: 'j' || symbol: 'j'
type spec : (INTEGER 4)
attributes: (VARIABLE )
symtree: 'merge' || symbol: 'merge'
type spec : (UNKNOWN 0)
attributes: (PROCEDURE INTRINSIC-PROC FUNCTION ARRAY-OUTER-DEPENDENCY)
result: merge
code:
ASSIGN fib:ifib __merge_i4[[((0) (1) ((< fib:i 1)))]]
IF (< fib:i 3)
RETURN
ENDIF
ASSIGN fib:fib_old(FULL) (/ 1 , 1 /)
DO fib:j=3 fib:i 1
ASSIGN fib:ifib (+ fib:fib_old(1) fib:fib_old(2))
IF (== fib:j fib:i)
EXIT
ENDIF
ASSIGN fib:fib_old(FULL) (/ fib:ifib , fib:fib_old(1) /)
END DO
Namespace: A-Z: (UNKNOWN 0)
procedure name = test_fib
symtree: 'fib' || symbol: 'fib'
type spec : (INTEGER 4)
attributes: (PROCEDURE MODULE-PROC USE-ASSOC(fib_mod) FUNCTION ELEMENTAL PURE ALWAYS-EXPLICIT)
result: ifib
Formal arglist: i
symtree: 'fib_mod' || symbol: 'fib_mod'
type spec : (UNKNOWN 0)
attributes: (MODULE USE-ASSOC(fib_mod))
symtree: 'test_fib' || symbol: 'test_fib'
type spec : (UNKNOWN 0)
attributes: (PROGRAM PUBLIC SUBROUTINE IS-MAIN-PROGRAM)
code:
WRITE UNIT=6 FMT=-1
TRANSFER 'fib(6) ='
TRANSFER fib[[((6))]]
DT_END__attribute__((fn spec (". r ")))
integer(kind=4) fib (integer(kind=4) & restrict i)
{
integer(kind=4) fib_old[2];
integer(kind=4) ifib;
integer(kind=4) j;
{
static integer(kind=4) A.0[2] = {1, 1};
ifib = (integer(kind=4)) (*i > 0);
if (*i <= 2)
{
return ifib;
}
L.1:;
(void) __builtin_memcpy ((void *) &fib_old, (void *) &A.0, 8);
{
integer(kind=4) D.4223;
D.4223 = *i;
j = 3;
while (1)
{
{
logical(kind=4) D.4226;
D.4226 = j > D.4223;
if (D.4226) goto L.3;
ifib = fib_old[0] + fib_old[1];
if (*i == j) goto L.3;
L.4:;
{
struct array01_integer(kind=4) atmp.1;
integer(kind=4) A.2[2];
typedef integer(kind=4) [2];
atmp.1.dtype = {.elem_len=4, .rank=1, .type=1};
atmp.1.dim[0].stride = 1;
atmp.1.dim[0].lbound = 0;
atmp.1.dim[0].ubound = 1;
atmp.1.span = 4;
atmp.1.data = (void * restrict) &A.2;
atmp.1.offset = 0;
(*(integer(kind=4)[2] * restrict) atmp.1.data)[0] = ifib;
(*(integer(kind=4)[2] * restrict) atmp.1.data)[1] = fib_old[0];
{
integer(kind=8) S.4;
S.4 = 0;
while (1)
{
if (S.4 > 1) goto L.5;
fib_old[S.4] = (*(integer(kind=4)[2] * restrict) atmp.1.data)[S.4];
S.4 = S.4 + 1;
}
L.5:;
}
}
L.2:;
j = j + 1;
}
}
L.3:;
}
}
return ifib;
}
__attribute__((fn spec (". ")))
void test_fib ()
{
{
struct __st_parameter_dt dt_parm.5;
dt_parm.5.common.filename = &"fib.f90"[1]{lb: 1 sz: 1};
dt_parm.5.common.line = 21;
dt_parm.5.common.flags = 128;
dt_parm.5.common.unit = 6;
_gfortran_st_write (&dt_parm.5);
_gfortran_transfer_character_write (&dt_parm.5, &"fib(6) ="[1]{lb: 1 sz: 1}, 8);
{
static integer(kind=4) C.4258 = 6;
integer(kind=4) D.4259;
D.4259 = fib (&C.4258);
_gfortran_transfer_integer_write (&dt_parm.5, &D.4259, 4);
}
_gfortran_st_write_done (&dt_parm.5);
}
}
__attribute__((externally_visible))
integer(kind=4) main (integer(kind=4) argc, character(kind=1) * * argv)
{
static integer(kind=4) options.6[7] = {2116, 4095, 0, 1, 1, 0, 31};
_gfortran_set_args (argc, argv);
_gfortran_set_options (7, &options.6[0]);
test_fib ();
return 0;
}Assembly code produced by gfortran -S -fverbose-asm fib.f90 on Windows, which shows the assembly corresponding to each source line.
# GNU Fortran2008 (GCC) version 12.0.1 20220213 (experimental) (x86_64-w64-mingw32)
# compiled by GNU C version 12.0.0 20220116 (experimental), GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version none
# GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
# options passed: -mtune=generic -march=x86-64 -fintrinsic-modules-path c:/equation/bin/../lib/gcc/x86_64-w64-mingw32/12.0.1/finclude
.text
.globl __fib_mod_MOD_fib
.def __fib_mod_MOD_fib; .scl 2; .type 32; .endef
.seh_proc __fib_mod_MOD_fib
__fib_mod_MOD_fib:
pushq %rbp #
.seh_pushreg %rbp
movq %rsp, %rbp #,
.seh_setframe %rbp, 0
subq $96, %rsp #,
.seh_stackalloc 96
.seh_endprologue
movq %rcx, 16(%rbp) # i, i
# fib.f90:7: ifib = merge(0, 1, i<1)
movq 16(%rbp), %rax # i, tmp99
movl (%rax), %eax # *i_21(D), _1
testl %eax, %eax # _1
setg %al #, tmp100
movzbl %al, %eax # tmp100, _2
movl %eax, -4(%rbp) # _2, ifib
# fib.f90:8: if (i < 3) return
movq 16(%rbp), %rax # i, tmp101
movl (%rax), %eax # *i_21(D), _3
cmpl $2, %eax #, _3
jg .L2 #,
# fib.f90:8: if (i < 3) return
movl -4(%rbp), %eax # ifib, _16
jmp .L9 #
.L2:
movq A.0.1(%rip), %rax # MEM <unsigned long long> [(c_char * {ref-all})&A.0], _23
# fib.f90:9: fib_old = [1,1]
movq %rax, -16(%rbp) # _23, MEM <unsigned long long> [(c_char * {ref-all})&fib_old]
# fib.f90:10: do j=3,i
movq 16(%rbp), %rax # i, tmp102
movl (%rax), %edx # *i_21(D), _25
# fib.f90:10: do j=3,i
movl $3, -8(%rbp) #, j
.L8:
# fib.f90:10: do j=3,i
cmpl %edx, -8(%rbp) # _25, j
setg %al #, tmp103
movzbl %al, %eax # tmp103, _27
testl %eax, %eax # _27
jne .L10 #,
# fib.f90:11: ifib = fib_old(1) + fib_old(2)
movl -16(%rbp), %ecx # fib_old[0], _4
movl -12(%rbp), %eax # fib_old[1], _5
addl %ecx, %eax # _4, tmp104
movl %eax, -4(%rbp) # tmp104, ifib
# fib.f90:12: if (j == i) exit
movq 16(%rbp), %rax # i, tmp105
movl (%rax), %eax # *i_21(D), _6
cmpl %eax, -8(%rbp) # _6, j
je .L11 #,
# fib.f90:13: fib_old = [ifib,fib_old(1)]
movq $0, -80(%rbp) #, atmp.1.dtype
movq $0, -72(%rbp) #, atmp.1.dtype
movq $4, -80(%rbp) #, atmp.1.dtype.elem_len
movb $1, -68(%rbp) #, atmp.1.dtype.rank
movb $1, -67(%rbp) #, atmp.1.dtype.type
movq $1, -56(%rbp) #, atmp.1.dim[0].stride
movq $0, -48(%rbp) #, atmp.1.dim[0].lbound
movq $1, -40(%rbp) #, atmp.1.dim[0].ubound
movq $4, -64(%rbp) #, atmp.1.span
leaq -24(%rbp), %rax #, tmp106
movq %rax, -96(%rbp) # tmp106, atmp.1.data
movq $0, -88(%rbp) #, atmp.1.offset
movq -96(%rbp), %rax # atmp.1.data, _7
movl -4(%rbp), %ecx # ifib, tmp107
movl %ecx, (%rax) # tmp107, MEM[(integer(kind=4)[2] *)_7][0]
movq -96(%rbp), %rax # atmp.1.data, _8
movl -16(%rbp), %ecx # fib_old[0], _9
movl %ecx, 4(%rax) # _9, MEM[(integer(kind=4)[2] *)_8][1]
movl $0, %eax #, S.4_15
.L7:
# fib.f90:13: fib_old = [ifib,fib_old(1)]
cmpq $1, %rax #, S.4_15
jg .L6 #,
# fib.f90:13: fib_old = [ifib,fib_old(1)]
movq -96(%rbp), %rcx # atmp.1.data, _10
movl (%rcx,%rax,4), %ecx # MEM[(integer(kind=4)[2] *)_10][S.4_15], _11
movl %ecx, -16(%rbp,%rax,4) # _11, fib_old[S.4_15]
addq $1, %rax #, S.4_15
jmp .L7 #
.L6:
# fib.f90:10: do j=3,i
addl $1, -8(%rbp) #, j
jmp .L8 #
.L10:
# fib.f90:13: fib_old = [ifib,fib_old(1)]
nop
jmp .L4 #
.L11:
# fib.f90:12: if (j == i) exit
nop
.L4:
# fib.f90:15: end function fib
movl -4(%rbp), %eax # ifib, _16
.L9:
# fib.f90:15: end function fib
addq $96, %rsp #,
popq %rbp #
ret
.seh_endproc
.section .rdata,"dr"
.LC0:
.ascii "fib.f90\0"
.LC1:
.ascii "fib(6) ="
.align 4
.LC2:
.long 6
.text
.def MAIN__; .scl 3; .type 32; .endef
.seh_proc MAIN__
MAIN__:
pushq %rbp #
.seh_pushreg %rbp
subq $576, %rsp #,
.seh_stackalloc 576
leaq 128(%rsp), %rbp #,
.seh_setframe %rbp, 128
.seh_endprologue
# fib.f90:21: print*,"fib(6) =",fib(6) ! 8
leaq .LC0(%rip), %rax #, tmp83
movq %rax, -88(%rbp) # tmp83, dt_parm.5.common.filename
movl $21, -80(%rbp) #, dt_parm.5.common.line
movl $128, -96(%rbp) #, dt_parm.5.common.flags
movl $6, -92(%rbp) #, dt_parm.5.common.unit
leaq -96(%rbp), %rax #, tmp84
movq %rax, %rcx # tmp84,
call _gfortran_st_write #
# fib.f90:21: print*,"fib(6) =",fib(6) ! 8
leaq -96(%rbp), %rax #, tmp85
movl $8, %r8d #,
leaq .LC1(%rip), %rdx #, tmp86
movq %rax, %rcx # tmp85,
call _gfortran_transfer_character_write #
# fib.f90:21: print*,"fib(6) =",fib(6) ! 8
leaq .LC2(%rip), %rax #, tmp87
movq %rax, %rcx # tmp87,
call __fib_mod_MOD_fib #
movl %eax, 444(%rbp) # _1, D.4259
leaq 444(%rbp), %rdx #, tmp88
leaq -96(%rbp), %rax #, tmp89
movl $4, %r8d #,
movq %rax, %rcx # tmp89,
call _gfortran_transfer_integer_write #
# fib.f90:21: print*,"fib(6) =",fib(6) ! 8
leaq -96(%rbp), %rax #, tmp90
movq %rax, %rcx # tmp90,
call _gfortran_st_write_done #
# fib.f90:22: end program test_fib
nop
addq $576, %rsp #,
popq %rbp #
ret
.seh_endproc
.def __main; .scl 2; .type 32; .endef
.globl main
.def main; .scl 2; .type 32; .endef
.seh_proc main
main:
pushq %rbp #
.seh_pushreg %rbp
movq %rsp, %rbp #,
.seh_setframe %rbp, 0
subq $32, %rsp #,
.seh_stackalloc 32
.seh_endprologue
movl %ecx, 16(%rbp) # argc, argc
movq %rdx, 24(%rbp) # argv, argv
# fib.f90:19: use fib_mod, only: fib
call __main #
movq 24(%rbp), %rdx # argv, tmp84
movl 16(%rbp), %eax # argc, tmp85
movl %eax, %ecx # tmp85,
call _gfortran_set_args #
leaq options.6.0(%rip), %rax #, tmp86
movq %rax, %rdx # tmp86,
movl $7, %ecx #,
call _gfortran_set_options #
call MAIN__ #
movl $0, %eax #, _7
addq $32, %rsp #,
popq %rbp #
ret
.seh_endproc
.section .rdata,"dr"
.align 8
A.0.1:
.long 1
.long 1
.align 16
options.6.0:
.long 2116
.long 4095
.long 0
.long 1
.long 1
.long 0
.long 31
.ident "GCC: (GNU) 12.0.1 20220213 (experimental)"
.def _gfortran_st_write; .scl 2; .type 32; .endef
.def _gfortran_transfer_character_write; .scl 2; .type 32; .endef
.def _gfortran_transfer_integer_write; .scl 2; .type 32; .endef
.def _gfortran_st_write_done; .scl 2; .type 32; .endef
.def _gfortran_set_args; .scl 2; .type 32; .endef
.def _gfortran_set_options; .scl 2; .type 32; .endef