Richard Suchenwirth 2013-11-30 - dis2asm, the converter from the language produced by tcl::unsupported::disassemble, to the one accepted by tcl::unsupported::assemble, TAL, had a troublesome issue: it could do for and while loops, but not foreach. Disassembling a foreach loop came out as
% aproc f x {foreach j $x {puts $j}}
ByteCode 0x0x9eaad68, refCt 1, epoch 16, interp 0x0x9e057a0 (epoch 16)
Source "foreach j $x {puts $j}"
Cmds 2, src 22, inst 29, litObjs 2, aux 1, stkDepth 2, code/src 0.00
Proc 0x0x9ebb820, refCt 1, args 1, compiled locals 4
slot 0, scalar, arg, "x"
slot 1, scalar, temp
slot 2, scalar, temp
slot 3, scalar, "j"
Exception ranges 1, depth 1:
0: level 0, loop, pc 17-22, continue 10, break 26
Commands 2:
1: pc 0-27, src 0-21 2: pc 17-22, src 14-20
Command 1: "foreach j $x {puts $j}"
(0) loadScalar1 %v0 # var "x"
(2) storeScalar1 %v1 # temp var 1
(4) pop
(5) foreach_start4 0
[data=[%v1], loop=%v2
it%v1 [%v3]]
(10) foreach_step4 0
[data=[%v1], loop=%v2
it%v1 [%v3]]
(15) jumpFalse1 +11 # pc 26
Command 2: "puts $j"
(17) push1 0 # "puts"
(19) loadScalar1 %v3 # var "j"
(21) invokeStk1 2
(23) pop
(24) jump1 -14 # pc 10
(26) push1 1 # ""
(28) done and in TAL there are no instructions foreach_start (see (5)) or foreach_step (see (10)). But I wanted them so badly...
Luckily it was weekend, and I had some time on my hands - so I made this my fun project of the day. At first, I manually coded a working solution in TAL:
proc foreachtest x {asm {
load x
listLength
store _l
push -1
store _i
label loop;
push puts
load x
load _i
listIndex
invokeStk 2
pop
incrImm _i +1
load _l
lt
jumpTrue loop
pop
pop
push {}
}}
foreachtest {a b c d}This uses two local variables, _i as index into the input list, and _l to hold the length of the list. The code at the puts invocation did however not match the disassembly above. So as next step, I restructured the code to look exactly like the disassembly, except for extra instructions to replace foreach_start and foreach_step - I considered them macros. So here is the second version, that meets that requirement:
proc foreachtest x {asm {
load x
store 1
pop
#foreach_start ;#
push -1 ;#
store 2 ;#
pop ;#
label L10
#foreach_step ;#
incrImm 2 +1 ;#
load 1 ;#
load 2 ;#
listIndex ;#
store i ;#
pop ;#
load 1 ;#
listLength ;#
lt ;#
jumpFalse L26
push puts
load i
invokeStk 2
pop
jump L10
label L26
push {}
}}
foreachtest {e f g h}
e
f
g
hThe macros are commented out, followed by their expansions also marked by a trailing comment. In the local variables, I accepted the numeric names
which are valid in Tcl as well. "i" now holds the current list element, like it should. The llength can be checked at runtime, no variable needed for that. There still was the problem that inside the expansion, "i" was mentioned (in the "store i" instruction), and could of course have any other name in practice (my counter-test was to use "j" instead ;^) So the macro had to be parametrized. Looking at the disassembly again, the local variable "slots" are listed:
slot 0, scalar, arg, "x"
slot 1, scalar, temp
slot 2, scalar, temp
slot 3, scalar, "j"The sequence is not the same as in the argument list, but that doesn't matter - the "temp" ones can use the slot number as their name. I save the slot info in a temporary array indexed by slot number. Now, the foreach_* macros each span three lines:
(5) foreach_start4 0
[data=[%v1], loop=%v2
it%v1 [%v3]]
(10) foreach_step4 0
[data=[%v1], loop=%v2
it%v1 [%v3]]and this is a little troublesome, as dis2asm processes one line at a time. Clearly, in the example
so I can parse these variables out of there. With foreach_start, I had to delay code generation until its third input line had been parsed.
Proof of the pudding: disassemble, reassemble, run:
% aproc f x {foreach j $x {puts $j}} -x
proc f x {asm {
load x ;# (0) loadScalar1 %v0 # var "x"
store 1 ;# (2) storeScalar1 %v1 # temp var 1
pop ;# (4) pop
push -1; store 2;pop ;# (5) foreach_start4 0
label L10;
incrImm 2 +1;load 1;load 2
listIndex;store j;pop
load 1;listLength;lt ;# (10) foreach_step4 0
jumpFalse L26 ;# (15) jumpFalse1 +11 # pc 26
push puts ;# (17) push1 0 # "puts"
load j ;# (19) loadScalar1 %v3 # var "j"
invokeStk 2 ;# (21) invokeStk1 2
pop ;# (23) pop
jump L10 ;# (24) jump1 -14 # pc 10
label L26;
push {} ;# (26) push1 1 # ""
;# (28) done
}}
% f {T A L}
T
A
LBoy, was I happy! This is still far away from a real, decent macro assembler, with the tests and the substitutions hard-wired in the code, but it is a good result for the 3 hours it took me to investigate and hack... The add_locals proc turned out to be unnecessary. The aproc wrapper got simpler:
proc aproc {name argl body args} {
proc $name $argl $body
set res [disasm proc $name]
if {"-x" in $args} {
set res [list proc $name $argl [list asm [dis2asm $res]]]
eval $res
}
return $res
}The dis2asm proc was extended in various ways. The macro expansions were put in variables fstart, fstep with place-holders @x to be substituted with the appropriate variable names:
proc dis2asm body {
set fstart " push -1; store @p; pop "
set fstep " incrImm @p +1;load @l;load @p
listIndex;store @i;pop
load @l;listLength;lt "
set res ""
set wait ""
set jumptargets {}
foreach line [split $body \n] { #-- pass 1: collect jump targets
if [regexp {\# pc (\d+)} $line -> pc] {lappend jumptargets $pc}
}
foreach line [split $body \n] {
set line [string trim $line]
if {$line eq ""} continue
set code ""
if {[regexp {slot (\d+), (.+)} $line -> number descr]} {
set slot($number) $descr
} elseif {[regexp {data=.+loop=%v(\d+)} $line -> ptr]} {
#got ptr, carry on
} elseif {[regexp {it%v(\d+).+\[%v(\d+)\]} $line -> copy number]} {
set loopvar [lindex $slot($number) end]
if {$wait ne ""} {
set map [list @p $ptr @i $loopvar @l $copy]
set code [string map $map $fstart]
append res "\n $code ;# $wait"
set wait ""
}
} elseif {[regexp {\((\d+)\) (.+)} $line -> pc instr]} {
if {$pc in $jumptargets} {append res "\n label L$pc;"}
if {[regexp {(.+)#(.+)} $instr -> instr comment]} {
set arg [list [lindex $comment end]]
if [string match jump* $instr] {set arg L$arg}
} else {set arg ""}
set instr0 [normalize [lindex $instr 0]]
switch -- $instr0 {
concat - invokeStk {set arg [lindex $instr end]}
incrImm {set arg [list $arg [lindex $instr end]]}
}
set code [format " %-24s" "$instr0 $arg"]
switch -- $instr0 {
startCommand {set code ""}
foreach_start {set wait $line; continue}
foreach_step {set code [string map $map $fstep]}
}
append res "\n $code ;# $line"
}
}
append res \n
return $res
}
Finally, to show that dis2asm can now deal well with nested foreach loops too:
% aproc f x {foreach i {a b} {foreach j $x {puts $i,$j}}} -x
proc f x {asm {
push {a b} ;# (0) push1 0 # "a b"
store 1 ;# (2) storeScalar1 %v1 # temp var 1
pop ;# (4) pop
push -1; store 2; pop ;# (5) foreach_start4 0
label L10;
incrImm 2 +1;load 1;load 2
listIndex;store i;pop
load 1;listLength;lt ;# (10) foreach_step4 0
jumpFalse L63 ;# (15) jumpFalse1 +48 # pc 63
;# (17) startCommand +43 1 # next cmd at pc 60
load x ;# (26) loadScalar1 %v0 # var "x"
store 4 ;# (28) storeScalar1 %v4 # temp var 4
pop ;# (30) pop
push -1; store 5; pop ;# (31) foreach_start4 1
label L36;
incrImm 5 +1;load 4;load 5
listIndex;store j;pop
load 4;listLength;lt ;# (36) foreach_step4 1
jumpFalse L58 ;# (41) jumpFalse1 +17 # pc 58
push puts ;# (43) push1 1 # "puts"
load i ;# (45) loadScalar1 %v3 # var "i"
push , ;# (47) push1 2 # ","
load j ;# (49) loadScalar1 %v6 # var "j"
concat 3 ;# (51) concat1 3
invokeStk 2 ;# (53) invokeStk1 2
pop ;# (55) pop
jump L36 ;# (56) jump1 -20 # pc 36
label L58;
push {} ;# (58) push1 3 # ""
pop ;# (60) pop
jump L10 ;# (61) jump1 -51 # pc 10
label L63;
push {} ;# (63) push1 3 # ""
;# (65) done
}}
% f {0 1}
a,0
a,1
b,0
b,1Now to look around for the next challenge, I have only used 25% of the weekend yet...
Consider the lines marked (58) and (60) in the last demo. First, the empty string is pushed (as result of foreach), but then popped away again. These two lines can be optimized out. There remains
label L58: jump L10
which can equally be weeded out, if all instances of "jump L58" (there is only one, at (41)) are rewritten to "jump L10". Tighter code (uses 5 bytes less), and will run (marginally) faster... The solution does not fit on the margin of this page, but see dis2asm gets better.
See also: dis2asm gets things done
RS 2013-12-05 - dkf pointed out that foreach has several more complex ways of calling - multiple lists, multiple iterators on one list. A simple example for both is
% proc f {x y} {foreach i $x {j k} $y {puts $i,$j,$k}}
% f {a b} {c d e f}
a,c,d
b,e,f
% disasm proc f
ByteCode 0x00F2C8D8, refCt 1, epoch 6, interp 0x00A60B70 (epoch 6)
Source "foreach i $x {j k} $y {puts $i,$j,$k}"
Cmds 2, src 37, inst 44, litObjs 3, aux 1, stkDepth 6, code/src 0.00
Proc 0x00F4A558, refCt 1, args 2, compiled locals 8
slot 0, scalar, arg, "x"
slot 1, scalar, arg, "y"
slot 2, scalar, temp
slot 3, scalar, temp
slot 4, scalar, temp
slot 5, scalar, "i"
slot 6, scalar, "j"
slot 7, scalar, "k"
Exception ranges 1, depth 1:
0: level 0, loop, pc 22-37, continue 15, break 41
Commands 2:
1: pc 0-42, src 0-36 2: pc 22-37, src 23-35
Command 1: "foreach i $x {j k} $y {puts $i,$j,$k}"
(0) loadScalar1 %v0 # var "x"
(2) storeScalar1 %v2 # temp var 2
(4) pop
(5) loadScalar1 %v1 # var "y"
(7) storeScalar1 %v3 # temp var 3
(9) pop
(10) foreach_start4 0
[data=[%v2, %v3], loop=%v4
it%v2 [%v5],
it%v3 [%v6, %v7]]
(15) foreach_step4 0
[data=[%v2, %v3], loop=%v4
it%v2 [%v5],
it%v3 [%v6, %v7]]
(20) jumpFalse1 +21 # pc 41
Command 2: "puts $i,$j,$k"
(22) push1 0 # "puts"
(24) loadScalar1 %v5 # var "i"
(26) push1 1 # ","
(28) loadScalar1 %v6 # var "j"
(30) push1 1 # ","
(32) loadScalar1 %v7 # var "k"
(34) concat1 5
(36) invokeStk1 2
(38) pop
(39) jump1 -24 # pc 15
(41) push1 2 # ""
(43) done Evidently, the extra lines following the foreach_start and foreach_step instructions are more expressive than I first thought.
data=[%v2, %v3]
enumerates the lists to iterate over. I'm not sure about loop=%v4, but the rest is quite clear again:
it%v2 [%v5],
it%v3 [%v6, %v7]]specify that %v5 ("i") is to iterate over the list copy %v2, while %v6 ("j") and %v7 ("k") iterate over %v3. As the number of extra lines depends on the number of lists, it will be better to parse for bracket balance, to be sure all extra lines have been processed.
As before, I first hand-coded what I thought may be the right expansion for the more complex foreach_* macros:
proc g {x y} {asm {
load x ;# make a local copy of x
store 2
pop
load y ;# ... and of y
store 3
pop
#foreach_start ;# initialize each of the iterators:
push -1 ;#
store 5 ;#
pop ;#
push -2 ;# initial value must be -stride (number of iterators)
store 6 ;#
pop ;#
push -1 ;# ... and incremented by one for each
store 7 ;#
pop ;#
label L10
#foreach_step ;#-------------------- begin macro expansion
incrImm 5 +1 ;#
load 2 ;#
load 5 ;#
listIndex ;#
store i ;# i := x[%v5]
pop ;#
load 2 ;#
listLength ;#
lt ;# leave on stack for the end
incrImm 6 +2 ;# increment by stride
load 3 ;#
load 6 ;#
listIndex ;#
store j ;# j := y[%v6]
pop ;#
load 3 ;#
listLength ;#
lt ;# leave on stack for the end
incrImm 7 +2 ;#
load 3 ;#
load 7 ;#
listIndex ;#
store k ;# k := y[%v7]
pop ;#
load 3 ;#
listLength ;#
lt ;# Now three "lt" results are on the stack.
lor ;# If at least one of them is true, we carry on.
lor ;#------------------ end of foreach_step macro expansion
jumpFalse L26
push puts
load i
push ,
load j
push ,
load k
concat 5
invokeStk 2
pop
jump L10
label L26
push {}
}}Now testing, with two iterators running out of data before the end:
% g {A B} {C D E F G}
A,C,D
B,E,F
,G,Seems to work right :^D Now to generalize the code generation...