Re: Backward branch, warnocked.

[Harry Jackson]

Pete Lomax wrote:
Leo clarified this as a problem with backward branch circa 3/12/03:

Sorry to be a pain in the butt, but I need to be told that there has
been no improvement in the last two months on this ;-(
..sub _main
        goto L1
test:
        $I1 = 1
        ret
L1:
        $I2 = 2
        call test
        print $I2               # prints 1, not 2
        end
..end
Surely it can't just be me that thinks this is rather fundamental?
How fundamental *is* the problem, can it *ever* be fixed?
Again, sorry to be a pain, but I'd like the truth/an update, please!
Or some hints... file level variables... better ways to code this...
Pete
PS use parrot -o and examine the output .pasm:, $I1 and $I2 (or
..local int i, .local int j) get assigned the same register.
Not sure if this answers your question. At the bottom of this email 
there is a bit taken from the IMCC.faq, I have pointed to the bit that I 
think may tell us what has happened. When the above piece of code gets 
converted to pasm we get

      1 _main:
      2         branch L1
      3 test:
      4         set I16, 1
      5         ret
      6 L1:
      7         set I16, 2
      8         bsr test
      9         print I16
     10         end
     11
     12
This is a branch not a subroutine call so IMCC as per the spec does not 
take care of the scoping in this case.

To code it using subs we could use

      1 .sub _main prototyped
      2    .sym Sub connect
      3    newsub   connect, .Sub, _connect
      4
      5     $I1 = 2
      6     .pcc_begin prototyped
      7           .pcc_call connect
      8           retconnect:
      9     .pcc_end
     10     print $I1
     11     end
     12 .end
     13
     14 .sub _connect
     15     $I1 = 1
     16     print $I1
     17     .pcc_begin_return
     18     .pcc_end_return
     19 .end
This prints

12

as expected.

Harry



Taken from the IMCC.faq

What are IMC variables?

IMC has 2 classes of variables, symbolic registers and named variables. 
Both are mapped to real registers, but there are a few minor 
differences. Named variables must be declared. They may be global or 
local, and may be qualified by a namespace. Symbolic registers, on the 
other hand, do not need declaration,

----->but their scope never extends outside of a subroutine unit.

Symbolics registers basically give compiler front ends an easy way to 
generate code from their parse trees or AST. To generate expressions 
compilers have to create temporaries.

Symbolic Registers (or Temporaries)

Symbolic registers have a $ sign for the first character, have single 
letter (S,N,I,P) for the second character, and 1 or more digits for the 
rest. By the 2nd character IMCC determines which set of Parrot registers 
it belongs to.