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   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. index:: shrink-wrapping separate components
   7
   8 .. _shrink-wrapping-separate-components:
   9
  10 Shrink-wrapping separate components
  11 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  12
  13 The prologue may perform a variety of target dependent tasks such as
  14 saving callee-saved registers, saving the return address, aligning the
  15 stack, creating a stack frame, initializing the PIC register, setting
  16 up the static chain, etc.
  17
  18 On some targets some of these tasks may be independent of others and
  19 thus may be shrink-wrapped separately.  These independent tasks are
  20 referred to as components and are handled generically by the target
  21 independent parts of GCC.
  22
  23 Using the following hooks those prologue or epilogue components can be
  24 shrink-wrapped separately, so that the initialization (and possibly
  25 teardown) those components do is not done as frequently on execution
  26 paths where this would unnecessary.
  27
  28 What exactly those components are is up to the target code; the generic
  29 code treats them abstractly, as a bit in an ``sbitmap``.  These
  30 ``sbitmap`` s are allocated by the ``shrink_wrap.get_separate_components``
  31 and ``shrink_wrap.components_for_bb`` hooks, and deallocated by the
  32 generic code.
  33
  34 .. include:: ../tm.rst.in
  35   :start-after: [TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS]
  36   :end-before: [TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS]
  37
  38
  39 .. include:: ../tm.rst.in
  40   :start-after: [TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB]
  41   :end-before: [TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB]
  42
  43
  44 .. include:: ../tm.rst.in
  45   :start-after: [TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS]
  46   :end-before: [TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS]
  47
  48
  49 .. include:: ../tm.rst.in
  50   :start-after: [TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS]
  51   :end-before: [TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS]
  52
  53
  54 .. include:: ../tm.rst.in
  55   :start-after: [TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS]
  56   :end-before: [TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS]
  57
  58
  59 .. include:: ../tm.rst.in
  60   :start-after: [TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS]
  61   :end-before: [TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS]