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GO Classes DPP | COMPILER|TAC

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1 1 vote

Consider the following C-style code segment:

while (a < b) {
    if (c < d) x = y + z;
    else x = y - z;
}


Assume this code is translated into Three-Address Code (TAC) using the minimum number of labels required to ensure:

  1. The $\verb|while|$ condition is evaluated at the start of every iteration.
     
  2. The $\verb|if-else|$ control flow correctly branches to either the $\verb|if|$ block or the $\verb|else|$ block.
     
  3. Control returns to the $\verb|while|$ condition check after the $\verb|if-else|$ statement finishes.
     
  4. There is a single exit label immediately following the loop.
     

What is the minimum number of labels required to represent this control flow?

1 Answer

1 1 vote 
L1: if a < b goto L2   // Label 1: Loop Header
    goto L4           // Label 4: Loop Exit

L2: if c < d goto L3  // Label 2: If-Condition
    x = y - z         // Fall-through for 'else'
    goto L1

L3: x = y + z         // Label 3: If-True block
    goto L1

L4: ...               // End of Loop


$\text { Minimum number of labels required is } 4$

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