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4.15.2.2 TC-6 Scheduling Samples

Once your eseq and call canonicalized, normalize cjumps: they must be followed by their “false” label. This goes in two steps:

  1. Split in basic blocks.

    A basic block is a sequence of code starting with a label, ending with a jump (conditional or not), and with no jumps, no labels inside.

  2. Build the traces.

    Now put all the basic blocks into a single sequence.


The following example highlights the need for new labels: at least one for the entry point, and one for the exit point: 

1 & 2

File 4.67: 1-and-2.tig

$ tc -L 1-and-2.tig
/* == Low Level Intermediate representation. == */
# Routine: _main
label main
# Prologue
# Body
seq
  label l3
  cjump ne
    const 1
    const 0
    name l0
    name l1
  label l1
  label l2
  jump
    name l4
  label l0
  jump
    name l2
  label l4
seq end
# Epilogue
label end

Example 4.107: tc -L 1-and-2.tig


The following example contains many jumps. Compare the HIR to the LIR: 

while 10 | 20 do if 30 | 40 then break else break

File 4.68: broken-while.tig

$ tc -H broken-while.tig
/* == High Level Intermediate representation. == */
# Routine: _main
label main
# Prologue
# Body
seq
  seq
    label l1
    seq
      cjump ne
        const 10
        const 0
        name l3
        name l4
      label l3
      cjump ne
        const 1
        const 0
        name l2
        name l0
      label l4
      cjump ne
        const 20
        const 0
        name l2
        name l0
    seq end
    label l2
    seq
      seq
        cjump ne
          const 30
          const 0
          name l8
          name l9
        label l8
        cjump ne
          const 1
          const 0
          name l5
          name l6
        label l9
        cjump ne
          const 40
          const 0
          name l5
          name l6
      seq end
      label l5
      jump
        name l0
      jump
        name l7
      label l6
      jump
        name l0
      label l7
    seq end
    jump
      name l1
    label l0
  seq end
  sxp
    const 0
seq end
# Epilogue
label end

Example 4.108: tc -H broken-while.tig

$ tc -L broken-while.tig
/* == Low Level Intermediate representation. == */
# Routine: _main
label main
# Prologue
# Body
seq
  label l10
  label l1
  cjump ne
    const 10
    const 0
    name l3
    name l4
  label l4
  cjump ne
    const 20
    const 0
    name l2
    name l0
  label l0
  jump
    name l11
  label l2
  cjump ne
    const 30
    const 0
    name l8
    name l9
  label l9
  cjump ne
    const 40
    const 0
    name l5
    name l6
  label l6
  jump
    name l0
  label l5
  jump
    name l0
  label l8
  cjump ne
    const 1
    const 0
    name l5
    name l13
  label l13
  jump
    name l6
  label l3
  cjump ne
    const 1
    const 0
    name l2
    name l14
  label l14
  jump
    name l0
  label l11
seq end
# Epilogue
label end

Example 4.109: tc -L broken-while.tig

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