From: anton@mips.complang.tuwien.ac.at
30 years ago I wrote a paper about Gforth's locals and also gave some
performance results [ertl94l]. Since then the implementation of
Gforth, and also of locals has changed quite a bit; in particular,
recently we have improved the code generated for TO .
So here I look at it again. As a first example, I look at the fib
benchmark (which has a one-off error, but that makes little difference):
no locals with a local
: fib ( n1 -- n2 ) : fib { n -- n2 }
dup 2 < if n 2 < if
drop 1 1
else else
dup n 1- recurse
1- recurse n 2 - recurse
swap 2 - recurse +
+ then ;
then ;
For 43 fib the performance results (AMD64 instructions, Skylake
cycles) are:
no locals with a local factor
13_805_561_653 15_012_002_369 1.09
41_475_949_910 48_490_119_217 1.17
So those of you who dislike locals can still point to worse
performance of code with locals on Gforth.
Another example is string comparison, where I compared three versions:
\ no locals
: strcmp1 ( addr1 u1 addr2 u2 -- n )
rot 2dup 2>r min 0 ?do ( a1 a2 )
over c@ over c@ - dup if
nip nip 2rdrop unloop exit then
drop
char+ swap char+ swap
loop
2drop r> r> - ;
\ locals with TO
: strcmp2
{ addr1 u1 addr2 u2 -- n }
u1 u2 min 0
?do
addr1 c@ addr2 c@ - dup if
unloop exit then
drop
addr1 char+ TO addr1
addr2 char+ TO addr2
loop
u1 u2 - ;
\ locals without TO
: strcmp3
{ addr1 u1 addr2 u2 -- n }
addr1 addr2
u1 u2 min 0
?do { s1 s2 }
s1 c@ s2 c@ - dup if
unloop exit then
drop
s1 char+ s2 char+
loop
2drop
u1 u2 - ;
I am too lazy to benchmark this, but here's the number of
native-instruction bytes in the inner loop:
129 strcmp1
128 strcmp2
149 strcmp3
Here's the code for body of the loop:
strcmp1 strcmp2 strcmp3
over 1->1 @local0 1->1 >l 1->1
mov $00[r13],r8 mov $00[r13],r8 mov rax,rbp
sub r13,$08 sub r13,$08 add r13,$08
mov r8,$10[r13] mov r8,$00[rbp] lea rbp,-$08[rbp]
c@ 1->1 c@ 1->1 mov -$08[rax],r8
movzx r8d,bytePTR[r8] movzx r8d,bytePTR[r8] mov r8,$00[r13]
over 1->2 @local2 1->2 >l @local0 1->1
mov r15,$08[r13] mov r15,$10[rbp] @local0
c@ 2->2 c@ 2->2 mov rax,rbp
movzx r15d,bytePTR[r15] movzx r15d,bytePTR[r15] lea rbp,-$08[rbp]
- 2->1 - 2->1 mov -$08[rax],r8
sub r8,r15 sub r8,r15 c@ 1->1
dup 1->2 dup 1->2 movzx r8d,bytePTR[r8]
mov r15,r8 mov r15,r8 @local1 1->2
?branch 2->1 ?branch 2->1 mov r15,$08[rbp]
c@ 2->2
add rbx,$68 add rbx,$68 movzx r15d,bytePTR[r15]
mov rax,[rbx] mov rax,[rbx] - 2->1
test r15,r15 test r15,r15 sub r8,r15
jnz $7FED3DB2C317 jnz $7FED3DB2C0DC dup 1->2
jmp eax jmp eax mov r15,r8
nip 1->1 unloop 1->1 ?branch 2->1
add r13,$08 add r14,$10
nip 1->1 lit 1->2 add rbx,$78
add r13,$08 #32 mov rax,[rbx]
2rdrop 1->1 sub rbx,$10 test r15,r15
add r14,$10 mov r15,-$08[rbx] jnz $7FED3DB2C208
unloop 1->1 lp+! 2->1 jmp eax
add r14,$10 add rbp,r15 unloop 1->1
s 1->1 ;s 1->1 add r14,$10
mov rbx,[r14] mov rbx,[r14] lit 1->2
add r14,$08 add r14,$08 #48
mov rax,[rbx] mov rax,[rbx] sub rbx,$10
jmp eax jmp eax mov r15,-$08[rbx]
drop 1->1 drop 1->1 lp+! 2->1
mov r8,$08[r13] mov r8,$08[r13] add rbp,r15
add r13,$08 add r13,$08 ;s 1->1
char+ 1->1 @local0 1->2 mov rbx,[r14]
add r8,$01 mov r15,$00[rbp] add r14,$08
swap 1->2 char+ 2->2 mov rax,[rbx]
mov r15,$08[r13] add r15,$01 jmp eax
add r13,$08 !local0 2->1 drop 1->0
char+ 2->2 mov $00[rbp],r15 @local0 0->1
add r15,$01 @local2 1->2 mov r8,$00[rbp]
swap 2->1 mov r15,$10[rbp] char+ 1->1
mov $00[r13],r15 char+ 2->2 add r8,$01
sub r13,$08 add r15,$01 @local1 1->1
(loop) 1->1 !local2 2->1 mov $00[r13],r8
mov $10[rbp],r15 sub r13,$08
sub rbx,$68 (loop) 1->1 mov r8,$08[rbp]
mov rax,[r14] char+ 1->1
add rax,$01 sub rbx,$68 add r8,$01
cmp $08[r14],rax mov rax,[r14] (loop)-lp+!# 1->1
mov [r14],rax add rax,$01
jz $7FED3DB2C36C cmp $08[r14],rax #16
mov rax,[rbx] mov [r14],rax add rbx,$40
jmp eax jz $7FED3DB2C130 mov rax,[r14]
mov rax,[rbx] mov rsi,-$10[rbx]
jmp eax add rax,$01
cmp $08[r14],rax
jz $7FED3DB2C25F
add rbp,-$08[rbx]
mov [r14],rax
mov rbx,rsi
mov rax,[rsi]
jmp eax
@InProceedings{ertl94l,
author = "M. Anton Ertl",
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