Premature code optimization case?

Leonardo Hirokazu De Souza Hamada

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Aug 14, 2021, 3:21:12 AM8/14/21

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Greetings to all,

I'm new to JAL, only using it a couple of month now.

So I have the following code:

;-------------------------------------------- START

-- Compiler: >=2.4q2

const Branch_A = 0
const Branch_B = 1
const Branch_C = 2

const byte strA[] = "A"
const byte strB[] = "B"
const byte strC[] = "C"

procedure optimize_me(byte in value) is
          case value of
               Branch_A: serial_hw_write(strA)
               Branch_B: serial_hw_write(strB)
               Branch_C: serial_hw_write(strC)
          end case
          forever loop
          end loop
end procedure

var bit maybe = false
if maybe then
   optimize_me(Branch_A)
end if
optimize_me(Branch_C)

;--------------------------------------------END

I noticed that as the compiler analyses the code path and sees the forever loop it tries to prune the case ramification for items that it considers unreachable.

Yet, what happens is that it tries to optimize the whole case block at the first call instance (Branch_A), leaving an incomplete compiled code for other cases, there are workarounds to it, this is just a comment to this behavior.

Thank-you,

Leonardo Hamada

The asm code it generates with default compiler options is:

; -----START ASM

l_optimize_me
;   55           case value of
;   56                Branch_A: serial_hw_write(strA)
                               movlw    65
                               call     l_serial_hw_write
                               goto     l__l413
;   57                Branch_B: serial_hw_write(strB)
;   58                Branch_C: serial_hw_write(strC)
l__l409
;   59           end case
l__l406
;   60           forever loop
l__l413
;   61           end loop
                               goto     l__l413
;   62 end procedure
l__l402
;   64 var bit maybe = false
                               bcf      v__bitbucket, 0,v__access ; maybe
;   65 if maybe then
                               btfsc    v__bitbucket, 0,v__access ; maybe
;   66    optimize_me(Branch_A)
                               call     l_optimize_me
;   67 end if
l__l416
;   68 optimize_me(Branch_C)
                               call     l_optimize_me
; 112 forever loop
l__l417
; 113 end loop
                               goto     l__l417
                               end

rob...@hotmail.com

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Aug 14, 2021, 3:36:54 AM8/14/21

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Hi Leonardo,

Welcome to JAL and Jallib!

Interesting case this optimization issue. Never seen it before. Need to find out why this happens.

Kind regards,

Rob

Op zaterdag 14 augustus 2021 om 09:21:12 UTC+2 schreef leonard...@ufra.edu.br:

Rob CJ

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Aug 14, 2021, 4:00:30 AM8/14/21

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Hi Leonardo,

First analysis shows that it has seems it has to do something with the procedure call in the case statement. If you replace it by e.g. something like value = value + 1 then the problems is gone.

I registered your issue under: Compiler optimization problem in case statement · Issue #21 · jallib/jalv2compiler (github.com)

Compiler optimization problem in case statement · Issue #21 · jallib/jalv2compiler

Given the following program, the compiler optimizes the code incorrectly, not generation code for Branch_B and Branch_C of the case statement. -- Sample program to show an optimization problem. inc...

github.com

Kind regards,

Rob

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Verzonden: zaterdag 14 augustus 2021 09:36
Aan: jallist <jal...@googlegroups.com>
Onderwerp: [jallist] Re: Premature code optimization case?

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Leonardo Hirokazu De Souza Hamada

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Aug 16, 2021, 7:53:43 PM8/16/21

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Hello,

Thanks for the response.

I did not mention in the first post but before realizing what has happening, I wrote the case block (the example is just a short code pattern) equivalent using "if...elsif..else" construct and I remember not having success either. So there's that.

Greetings,

Leonardo

Rob CJ

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Aug 17, 2021, 1:15:33 PM8/17/21

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Hi Leonardo,

If I use if-elsif then I it seem to be OK, so using this in the program:

procedure optimize_me(byte in value) is          case value of

               Branch_A: do_something(value) 
               Branch_B: do_something(value) -- Incorrectly optimzed away             
               Branch_C: do_something(value) -- Incorrectly optimized way  

          end case
         forever loop
         end loop
end procedure

procedure optimize_me_too(byte in value) is
   if value == Branch_A then
      do_something(value) 
   elsif value == Branch_B then
      do_something(value) 
   elsif value == Branch_C then
      do_something(value) 
   end if 
end procedure

Results in this assembly code:

; d:\PIC\Compiler\Test\Issues\Issue#21\Optimize.jal

; 9 procedure do_something(byte in what) is

l_do_something

movwf v___what_1

; 10 what = what + 1

incf v___what_1,f

; 11 end procedure

return

; 18 procedure optimize_me(byte in value) is

l_optimize_me

movlb 0

movwf v___value_1

; 19 case value of

; 20 Branch_A: do_something(value)

call l_do_something

movlp HIGH l__l83

goto l__l83

; 21 Branch_B: do_something(value) -- Incorrectly optimzed away

; 22 Branch_C: do_something(value) -- Incorrectly optimized way

l__l79

; 23 end case

l__l76

; 24 forever loop

l__l83

; 25 end loop

goto l__l83

; 28 procedure optimize_me_too(byte in value) is

l_optimize_me_too

movlb 0

movwf v___value_3

; 29 if value == Branch_A then

movf v___value_3,w

btfss v__status, v__z

goto l__l88

; 30 do_something(value)

movf v___value_3,w

goto l_do_something

; 31 elsif value == Branch_B then

l__l88

decf v___value_3,w

btfss v__status, v__z

goto l__l89

; 32 do_something(value)

movf v___value_3,w

goto l_do_something

; 33 elsif value == Branch_C then

l__l89

movlw 2

subwf v___value_3,w

btfss v__status, v__z

goto l__l90

; 34 do_something(value)

movf v___value_3,w

goto l_do_something

; 35 end if

l__l90

l__l87

; 36 end procedure

return

Kind regards,

Rob

Van: 'Leonardo Hirokazu De Souza Hamada' via jallist <jal...@googlegroups.com>
Verzonden: dinsdag 17 augustus 2021 01:53
Aan: jallist <jal...@googlegroups.com>
Onderwerp: Re: [jallist] Re: Premature code optimization case?

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