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Add VARRAY_FOREACH and VPTRS_ITER macros to iterate over arrays and pointer arrays #4239

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Add VARRAY_FOREACH and VPTRS_ITER macros to iterate over arrays and pointer arrays #4239

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Commits on Nov 28, 2024

  1. Add VARRAY_FOREACH macro for array iteration 

    This macro is intended to simplify loops over elements of an array using pointer
arithmetic instead of an array index.

The usual pattern of iterating over the array index and then accessing the i-th
element of the array is replaced with calculating the end pointer and looping
over the array elements.

The macro basically implements

	for (pointer = array, end = array + length; pointer < end; pointer++)

This pattern is more efficient but less clear to read when written out. The
macro is similar to the *_FOREACH pattern which we already use in many other
places with trees, lists and queues, but declares the loop variable locally.

Remarks on the implementation:

- typeof() is now formalized with C23 but has been a GNU extension for long. We
  use typeof() since e1ac593 as of March 2021.

- The construct 'typeof(*(arr)) * var' (using the element type declaring a
  pointer on it) is used to un-const arr while keeping the constness of the
  element type: If arr is const, '(typeof arr) var = arr' does not work because
  var can not be modified.

  The additional (typeof(var)) cast is to avoid a Flexelint warning (reference
  to pointer).
    @nigoroll
    nigoroll committed Nov 28, 2024
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  2. Add a semantic patch and start using VARRAY_FOREACH 

    The coccinelle patch only catches some cases, makes spatch enter a spinloop and
the patch result needs manual polish on top, but at this point the purpose is
only to show use cases for the new macro.
    @nigoroll
    nigoroll committed Nov 28, 2024
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  3. Add VPTRS_ITER to further simplify our "array of pointers" case 

    Based on VARRAY_FOREACH, this additional macro further simplifies the case of
arrays of pointer as, for example, used in struct strands.

Here, the loop variable is to be declared outside the macro to support keeping
found elements from within the loop.
    @nigoroll
    nigoroll committed Nov 28, 2024
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  4. Use VPTRS_ITER 

    we add a semantic patch to turn VARRAY_FOREACH cases into VPTRS_ITER cases where
applicable.
    @nigoroll
    nigoroll committed Nov 28, 2024
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