LLVM Tutorial #25: Mandelbrot?

In this series I walkthrough the LLVM "Kaleidoscope" Tutorial, where you follow step by step to create your first programming language frontend using LLVM as the backend. Last time we finished up the code for custom operators but ran into some bugs. This time we spend some time debugging and make an encounter our most beloved mathematician :)

Transcript

The following transcript was automatically generated by an algorithm.

00:00 : okay welcome back to this series
00:03 : where we walk through this llvm tutorial
00:06 : on the llvm.org website the tutorial is
00:09 : called my first
00:11 : language front end using llvm
00:14 : we're doing the c plus plus version
00:17 : uh there's also an old camel version but
00:19 : we're gonna we're doing the c
00:21 : plus plus we're through the first uh
00:25 : five chapters and we're almost through
00:27 : to the
00:29 : sixth chapter but uh i have a bug in my
00:32 : program
00:33 : um i assume though the code from the
00:36 : code listing
00:38 : does work um
00:42 : let me just verify that so that in case
00:45 : i need to call on
00:47 : the their code
00:50 : as a means for debugging
00:54 : then i can that that can give me an
00:57 : easier time i think
01:02 : okay so this is their code
01:06 : i'm gonna call this
01:10 : their code
01:13 : dot zero six or not dot
01:17 : dash zero six again i'm gonna try to
01:20 : compile their code
01:27 : oh wait you have to change
01:30 : the include
01:38 : location
01:46 : oh i have trouble compiling their code
01:51 : no member named get data layout
02:01 : did their last version compile
02:12 : i didn't remember testing this
02:15 : their last version did compile
02:19 : but the newer version does not compile
02:27 : what did they change
02:49 : no member named kit data layout
02:58 : i have get data layout in this
03:02 : chapter 6 code but no get data layout in
03:05 : the chapter 5
03:06 : code i see something has
03:09 : changed i think they've changed this
03:13 : tutorial
03:17 : and i have a feeling
03:21 : they did that recently maybe
03:24 : and probably
03:38 : i'm gonna double check their
03:43 : chapter five code
03:49 : yes they change all of their code
03:52 : i think
03:54 : [Music]
03:57 : this set data layout thing
04:08 : i could either try to debug
04:12 : hmm their code but i
04:15 : feel like i rather try to debug my code
04:19 : i'm gonna just try to debug my code okay
04:21 : probably just made a
04:23 : mistake somewhere
04:54 : okay um so when i run this code
05:19 : let me see here how do you write code in
05:23 : this
05:24 : uh
05:25 : [Music]
05:32 : i forgot the syntax for the extern
05:34 : statement
05:35 : let me just go find it
05:46 : okay it looks like this
05:50 : print d x dot
05:54 : unknown token when expecting an
05:58 : expression
06:04 : i'm gonna search for that error message
06:10 : unknown token when expecting an
06:13 : expression
06:16 : so then get
06:40 : hmm cars
06:43 : primary i'm gonna
06:47 : print out the um
06:55 : like i wonder when this was happening
06:57 : right
06:58 : um it's trying to parse primary
07:11 : oneplus 2 is having well everything is
07:14 : having problems now
07:19 : oneplus one is not even generating
07:21 : anything
07:24 : um
07:29 : one
07:33 : something really really wrong has
07:36 : happened
07:36 : so i'm gonna try to go to the top level
07:42 : where this
07:46 : top level expression is
07:50 : is getting red
07:54 : and maybe try to do some debugging there
07:56 : [Music]
08:01 : this is the main loop we're gonna ignore
08:04 : semicolons um
08:09 : handle top level expression
08:16 : we're going to parse the top level
08:18 : expression
08:21 : and then code gen so here i guess i will
08:24 : say
08:25 : something like
08:31 : pars complete
08:38 : so that i know the parts actually worked
08:40 : chances are the
08:41 : parser had some problems is what i'm
08:45 : expecting
08:46 : um okay
08:50 : let me build this again
09:14 : well it didn't say parse complete
09:19 : so that's a problem
09:35 : i think i'm going to
09:40 : use the debugger
09:45 : here's the lldb debugger
09:50 : and then i'm gonna pause on this
09:54 : like 9 17 i believe
09:57 : so i think the way to set a breakpoint
09:59 : is say
10:02 : b
10:06 : the file name colon and then the
10:10 : line number and then i'm going to run it
10:12 : the r command
10:18 : um okay okay we're paused here
10:22 : i'm gonna step through this baby line by
10:26 : line
10:27 : um let me see
10:32 : my suspicion is it never made it
10:35 : back to this line
10:40 : i guess i'm going to step in i forget
10:43 : the command
10:45 : let me do help
10:48 : so i can stepping into calls so i want
10:51 : to do s
10:52 : to step in and then i believe n
10:56 : means next it steps over calls so i want
10:59 : to step in
11:02 : okay so we're going to parse unreal
11:04 : expression
11:07 : i'm going to step over this one
11:11 : it's going to parse a primary
11:14 : and the current token
11:21 : is a number which makes sense
11:24 : uh let's step in there
11:28 : the number value i think i can
11:32 : print can i do this
11:36 : i can i can print the number value um
11:42 : the number value is one i'm gonna step
11:44 : over this
11:45 : and then it's gonna return
11:51 : okay sounds good it's gonna so the first
11:53 : call to
11:54 : parts primary returned a number
11:58 : presumably we're on line 769 now
12:04 : we're on this line and that returned
12:10 : and then now we're going into this par
12:12 : spin
12:13 : up right hand side
12:16 : i'm gonna get the token presidents
12:20 : um i'm gonna print out what that is
12:26 : is zero
12:41 : uh why is it zero
12:45 : where is the current token current token
12:47 : is 43
12:51 : consult the ascii table
12:54 : what's 43
12:58 : 43 is the plus symbol
13:02 : oh we didn't instantiate the
13:06 : um the
13:09 : the token table whoops
13:14 : okay i can print the
13:22 : so that's a problem probably
13:26 : this precedence
13:29 : um that's got a this is a map
13:33 : but we haven't put entries in the map
13:37 : uh we probably need to do that so i'm
13:41 : i'm gonna go find the code that is doing
13:46 : that
13:52 : ah does it in the main function okay
13:56 : i will do that
14:13 : okay fix that and then recompile it
14:18 : um i don't know if it fixes the problem
14:21 : or not
14:22 : but uh
14:25 : maybe not but we'll see how
14:28 : we'll see what happens
14:40 : i'm going to send the same brick point
14:43 : run it do one plus one again
14:48 : step into it i'm gonna skip over that
14:51 : one and go directly into the binary one
14:54 : okay so this time hopefully we will
14:58 : actually have a
14:59 : token president yeah of 20.
15:03 : that is correct that's the presidency of
15:05 : the plus operator
15:08 : uh what is the expression presidents
15:12 : zero so
15:16 : um so we're gonna do this next clause
15:20 : here i'm gonna parse unary again
15:29 : oh
15:33 : all right no we're fine
15:36 : let's step into this parse primary now
15:40 : and it's a number
15:44 : so okay i'm gonna step over this one
15:47 : so i have two numbers now this is gonna
15:50 : return the number
15:52 : and at this point if we we have a right
15:56 : hand side
15:58 : right hand side is this
16:02 : i can't really read this
16:05 : but presumably right hand side is an ast
16:20 : node
16:36 : oh
16:45 : the next president says zero
17:13 : so the president is not less than the
17:16 : next president
17:17 : so we go down here and we're ready to
17:21 : return this
17:22 : node that sounds right
17:32 : we're on line 784 now
17:37 : here and we're gonna continue
17:48 : we're gonna do some more
18:19 : um okay so
18:22 : this is not it's because this is not
18:25 : true we need this to return
18:27 : negative one i believe
18:30 : and that's probably what their listing
18:33 : did
18:34 : let me think
18:39 : probably wanted to if it would have been
18:42 : a zero
18:44 : then return negative one
18:47 : yes if it's zero
18:51 : okay that makes sense now
18:59 : i'm just gonna say if it is
19:02 : zero return negative one
19:08 : house
19:13 : okay
19:21 : to get the negative we need a negative
19:23 : one
19:24 : to be less than the zero
19:29 : on the while true line
19:34 : on this line we need we need this
19:37 : to go so that i would just return the
19:40 : left hand side
19:41 : to stop this while loop from going
19:47 : so i'm gonna just
19:50 : test this normal
19:54 : yes that worked uh okay
19:58 : now let's try some fancy stuff
20:02 : hopefully that fixed it
20:09 : all right am i able to do something like
20:11 : this now
20:14 : put char d 48 or something
20:19 : yes it can print zero um
20:24 : all right i'm gonna do this next print d
20:28 : print d can do print a number
20:40 : we don't have print d
20:44 : on the system
20:56 : we don't have print d whoops okay
21:05 : maybe print d is a function that linux
21:08 : has
21:10 : but on my mac i don't have it it's
21:14 : possible
21:16 : no manual entry for print d
21:22 : oh i didn't need to rebuild it but
21:25 : anyway i did
21:30 : okay uh so i'm gonna try
21:33 : x turn put
21:37 : chardee
21:40 : put the
21:44 : 53 it prints this
21:48 : 5 over here i
21:51 : probably should fix my printing so that
21:54 : they it doesn't get jammed onto the same
21:57 : line
22:02 : but i'm gonna try this
22:07 : colon thing ah
22:10 : that did not work we have more bugs
22:14 : uh expected function name
22:17 : in prototype we did have a parse
22:21 : complete
22:23 : but then we have a unknown array
22:26 : operator
22:29 : log error expected function name in
22:31 : prototype okay
22:32 : let me try this
22:38 : so there's two places where we print
22:41 : that
22:47 : both of them are in the parse prototype
22:49 : function
22:50 : so let me see
22:53 : so that's probably the error in the
22:56 : parse
22:56 : so i'm just gonna do a debugger again
23:02 : and i'm gonna pause in here so this
23:05 : is line 820 i'm gonna set a breakpoint
23:10 : here
23:14 : okay um
23:27 : let's run it and then this time
23:30 : i'm gonna do
23:33 : this binary thing
23:46 : okay i don't even understand this line
23:49 : of
23:50 : code like what what is it doing here
23:53 : it just returns zero
24:02 : oh okay i think i understand
24:06 : what it's doing actually
24:10 : um okay
24:13 : [Music]
24:16 : so
24:18 : let's try to parse this prototype
24:22 : so if it's not a token what
24:25 : i'm going to print out the current token
24:27 : what is the current token it's negative
24:30 : 11. what is negative
24:33 : 11 it's the word binary
24:37 : so if it's not a token identifier
24:43 : oh okay i get it now
24:47 : i'm gonna go to i should not have this
24:52 : this check should go away
24:56 : i got it now because that that check was
24:59 : disallowing
25:01 : uh my binary and honorary
25:04 : operator declaration
25:07 : so that's why um that check
25:11 : actually went over to here
25:15 : or something well
25:19 : here
25:27 : yep okay
25:30 : let's try to build it again and hope
25:33 : that this time
25:34 : it is actually fixed
25:55 : okay i'm gonna try that again
26:01 : just binary thing oh
26:04 : that worked yes i'm gonna do this
26:07 : i'm not gonna do print d because we
26:10 : found out that doesn't work
26:12 : on my computer i'm going to do x
26:15 : turn put char d
26:19 : x okay so now i can put
26:22 : her d 48
26:27 : but i can also put char d
26:31 : 48 colon put chard d
26:35 : 49
26:42 : semicolon and then
26:45 : that printed zero one and two that's
26:48 : awesome
26:48 : uh i this this thing is starting to
26:51 : annoy me so
26:55 : um what i'm gonna do is put a new line
26:59 : before that evaluated to is printed
27:04 : so that we can we can see the output
27:09 : sort of separated out by itself
27:14 : so basically the way that this this
27:17 : colon
27:18 : works is just by you just
27:21 : can put multiple statements on the line
27:23 : is more or less
27:24 : what that's doing for you or you just
27:28 : combine this guy like this is
27:32 : x here this is y
27:35 : you just evaluate all of them on one
27:38 : line that's all that's doing
27:40 : we can also define a bunch of other
27:42 : primitive operations
27:44 : such as these so why don't we do that
27:49 : okay so
27:53 : yeah let's define some of these let's
27:55 : play with
27:56 : these things
28:06 : okay i'm going to try this unreading
28:10 : define honorary exclamation point
28:13 : of v value
28:19 : which is if value then zero
28:22 : else one
28:28 : so not a one
28:33 : evaluates to zero not of zero
28:37 : evaluates to one not a five
28:40 : evaluates to zero not not
28:44 : of 6 is 1.
28:48 : that makes sense
28:51 : we have an unread negative
28:54 : the 100 negate so while we can do
28:58 : one minus two we can also do
29:01 : unread negate
29:05 : zero minus the value
29:08 : that's actually surprising so negative
29:11 : 45
29:12 : is negative 45 so i can do negative
29:15 : seven
29:16 : plus three negative four
29:20 : wow all right that that is awesome
29:22 : that's actually awesome
29:24 : uh we can do uh greater than
29:28 : now previously we only had
29:31 : less than so like three greater than
29:34 : four
29:35 : doesn't work as sick falls
29:40 : three greater than four six volts but
29:43 : if we define what greater than means
29:48 : i'm gonna do a space with
29:51 : presidents of ten okay that's a little
29:53 : weird
29:54 : i'm gonna do it like this l and r
29:58 : are less than l okay i'm just i'm just
30:02 : copying
30:02 : from here taking some liberties
30:06 : with the variable naming so now i can do
30:09 : three
30:10 : greater than four and it does not say
30:13 : fault that is hilarious
30:17 : okay three greater than four
30:21 : three greater than four is
30:24 : zero four greater than three
30:28 : is one okay beautiful um
30:32 : and then we have the logical and and so
30:35 : forth
30:37 : given the previous if then else support
30:41 : we can also define
30:42 : interesting functions for io
30:45 : for example the following prints out a
30:48 : character whose density
30:50 : reflects the value passed in
30:53 : oh i love this i love this this is like
30:56 : ascii art
30:58 : um so i'm gonna i'm gonna follow
31:02 : this code and say
31:07 : uh let's do x turn put char d first
31:12 : and then we'll do diff print then city
31:20 : um if
31:23 : d is greater than 8 then
31:30 : put char 32 which
31:34 : is the um
31:39 : space
31:42 : else if t is greater than four
31:46 : then
31:49 : put char d 46
31:53 : which is a dot else
31:57 : if d is greater than 2 then
32:01 : put e 43
32:07 : else put rd
32:12 : 42 this is the star
32:17 : semicolon oh that's a lot of code
32:20 : generated
32:21 : awesome now we can do
32:26 : this
32:29 : no whoops
32:33 : uh why is there a sick fall
32:37 : unknown honorary operator
32:40 : oh i didn't define this just binary
32:44 : thing
32:44 : okay ouch all right we'll try again
32:49 : we can do it i'm just gonna copy it
32:53 : this time instead of typing it all out
32:58 : i will need to define this binary
33:00 : operator
33:02 : and i think that's it
33:10 : and then we can do this
33:15 : unknown function referenced
33:25 : all right
33:29 : i'll do it one by one it hasn't crashed
33:32 : yet oh
33:33 : still unknown function referenced
33:37 : [Music]
33:49 : oh this comments do we support comments
33:54 : probably not right
33:57 : you might need to get rid of these
33:58 : comments i don't remember writing code
34:01 : to support comments
34:12 : unknown token wait
34:15 : let me try again
34:32 : oh it's to put put chardee that wasn't
34:35 : defined
34:36 : i see let me try again
34:52 : unknown token when expecting an
34:54 : expression
34:55 : that this just didn't work
35:00 : hmm
35:07 : i'm gonna try to type it in again
35:21 : unknown token oh because
35:25 : we haven't defined the greater than
35:29 : operate
35:34 : all right we need this i might just
35:38 : put all the code we need
35:42 : here in the same file
35:47 : hilarious
35:51 : uh and we need this next turn statement
35:55 : okay we do have this and then let's have
35:58 : this guy
36:03 : okay try again
36:12 : did they work
36:15 : i think that maybe worked
36:23 : yes it printed this stuff
36:27 : perfect okay i got it to work
36:31 : all right it's funny it's it's very
36:34 : funny
36:34 : it is interesting the dependency thing
36:38 : like it's not very it
36:41 : like you use the greater than operator
36:44 : without
36:45 : having to define it already
36:49 : and uh
36:53 : whereas in say javascript with a module
36:56 : system you can tell
36:59 : what modules you're importing and
37:01 : therefore what code you need to bring in
37:03 : uh here it's a little harder too but
37:07 : but the idea of custom operators is very
37:10 : intriguing i must say
37:11 : anyway um i think this works i'm going
37:14 : to try to run
37:16 : their mandelbrot set thing uh
37:19 : handle broadset is a fascinating
37:22 : piece of mathematics i actually
37:25 : previously
37:26 : had done a video about mandelbrot set
37:29 : this tutorial is going to walk me
37:32 : through
37:35 : doing this in the terminal
37:38 : using kaleidoscope and i think that's
37:41 : amazing i think that's really amazing
37:44 : i also think maybe i need some of these
37:47 : things i'm not sure
37:50 : is it using this and no
37:53 : is it using or do i need negative
37:57 : under i'm gonna put this in
38:01 : just in case
38:08 : and let me see there's a
38:12 : okay
38:16 : he's gonna just
38:20 : write the code to compute mandopratz
38:26 : that's hilarious okay
38:32 : okay will this work
38:39 : uh unknown token
38:43 : unknown variable name oh it does need
38:47 : this or
38:47 : operator that's
38:51 : i'm just gonna put all of his code in
39:02 : this is incredible um
39:05 : i'll put the n in just in case
39:09 : i didn't see him using it but
39:15 : okay equals
39:28 : uh i think i had the binary
39:31 : ordinary negative
39:35 : we had that exclamation point let's
39:40 : just put that in as well just in case
39:45 : okay all right
39:48 : okay
39:55 : what just happened
40:00 : okay
40:06 : okay i i think
40:10 : i don't see any errors so i'm gonna
40:12 : assume
40:13 : all that stuff worked
40:17 : mando help and mandel
40:32 : nando help i think that's a helper
40:35 : function
40:37 : of some sort and we have mendel
40:50 : okay
40:52 : let's try defining mando help
40:57 : i think let's do define mendel
41:04 : okay
41:06 : all right let's see let's see if we have
41:09 : magic here
41:13 : oh my god oh my god
41:18 : there is the mandelbrot set wow that's
41:21 : incredible
41:23 : that is incredible um
41:32 : wow that is really incredible that uh i
41:35 : mean
41:35 : i i didn't read this code or understand
41:39 : this code
41:39 : but uh i mean this is a very very little
41:42 : code
41:43 : to get that to happen um and again if
41:46 : you don't know what the mando brought
41:47 : set
41:48 : is uh google it
41:52 : and uh if you like to watch me explain
41:55 : it then you can
41:56 : google for my video on the mandelbrot
41:59 : set
42:00 : so you can use different parameters
42:03 : whoa that's crazy
42:13 : okay all right at this point you might
42:16 : be starting to realize that
42:18 : kaleidoscope is a real and powerful
42:21 : language it may not be self-similar
42:26 : i don't understand what that means but
42:29 : it can be used to plot things that are
42:34 : okay with this we conclude the add user
42:38 : define operators chapter so we we finish
42:41 : chapter six okay congratulations
42:44 : to you for following this for a long
42:47 : and i will i will see you next time when
42:51 : i go to the next chapter