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Editorial Team
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Asked: 2026-05-25T01:12:19+00:00

I’m trying to introduce Hoopl into some compiler and faced some problem: creating a

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I’m trying to introduce Hoopl into some compiler and faced some problem: creating
a graph for Hoopl makes the nodes to appear in order of labels that were introduced.

Eg:

(define (test) (if (eq? (random) 1 ) 2 (if (eq? (random) 2 ) 3 0) ) )

“compiles” to

L25:    call-direct random  -> _tmp7_6
    branch L27
L26:    return RETVAL
L27:    iconst 1 _tmp8_7
    branch L28
L28:    call-direct eq? _tmp7_6, _tmp8_7 -> _tmp4_8
    branch L29
L29:    cond-branch _tmp4_8 L30 L31
L30:    iconst 2 RETVAL
    branch L26
L31:    call-direct random  -> _tmp12_10
    branch L32
L32:    iconst 2 _tmp13_11
    branch L33
L33:    call-direct eq? _tmp12_10, _tmp13_11 -> _tmp9_12
    branch L34
L34:    cond-branch _tmp9_12 L36 L37
L35:    assign RETVAL _tmp6_15
    branch L26
L36:    iconst 3 _tmp6_15
    branch L35
L37:    iconst 0 _tmp6_15
    branch L35

The order of instructions (in order of showGraph) is strange, because of order of
recursive graph building from the AST. In order to generate code I need to reorder blocks in more natural way, say place return RETVAL to the end of function, merge blocks like this 

    branch Lx:
Lx: ...

into the one block, and so on. Seems that I need something like:

block1 = get block
Ln = get_last jump
block2 = find block Ln
if (some conditions) 
    remove block2
    replace blick1 (merge block1 block2)

I’m totally confused how to perform this with Hoopl. Of course, I may dump all the nodes
and then perform the transformations outside the Hoopl framework, but I believe that this
is bad idea.

May someone give me any glue? I did not find any useful examples. Something similar is performed in Lambdachine project, but seems too complicated.

There is also an another question. Is there any point to make all Call instruction non-local?
What the point of this considering that implementation of Call is not changing any local
variables and always transfer the control to the next instruction of the block? If Call instructions are defined like

data Insn e x where
   Call :: [Expr] -> Expr -> Label :: Insn O C -- last instruction of the block

that cause the graph to looks even more strange. So I use

-- what the difference with any other primitive, like "add a b -> c" 
Call :: [Expr] -> Expr -> Label :: Insn O O

May be I’m wrong with this?

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1 Answer

  1. Editorial Team

    I’ve found and tried a couple of ways to do the trick:

    1. Using foldBlockNodesF3 function or other foldBlockNodes… functions
    2. Using preorder_dfs* functions (like in Lambdachine project)
    3. Build the graph with larger blocks from the start

    The last option is not useful for me, because FactBase is linked with labels, so every instruction that change a liveness of the variables should have a label for using in the following analysis.

    So, my final solution is to use foldBlockNodesF3 function and linearize the graph and delete extra labels manually with simultaneous register allocation

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