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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:: return values in registers, values, returned by functions, scalars, returned as values
   7
   8 .. _scalar-return:
   9
  10 How Scalar Function Values Are Returned
  11 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  12
  13 This section discusses the macros that control returning scalars as
  14 values---values that can fit in registers.
  15
  16 .. include:: ../tm.rst.in
  17   :start-after: [TARGET_FUNCTION_VALUE]
  18   :end-before: [TARGET_FUNCTION_VALUE]
  19
  20
  21 .. c:macro:: FUNCTION_VALUE (valtype, func)
  22
  23   This macro has been deprecated.  Use ``TARGET_FUNCTION_VALUE`` for
  24   a new target instead.
  25
  26 .. c:macro:: LIBCALL_VALUE (mode)
  27
  28   A C expression to create an RTX representing the place where a library
  29   function returns a value of mode :samp:`{mode}`.
  30
  31   Note that 'library function' in this context means a compiler
  32   support routine, used to perform arithmetic, whose name is known
  33   specially by the compiler and was not mentioned in the C code being
  34   compiled.
  35
  36 .. include:: ../tm.rst.in
  37   :start-after: [TARGET_LIBCALL_VALUE]
  38   :end-before: [TARGET_LIBCALL_VALUE]
  39
  40
  41 .. c:macro:: FUNCTION_VALUE_REGNO_P (regno)
  42
  43   A C expression that is nonzero if :samp:`{regno}` is the number of a hard
  44   register in which the values of called function may come back.
  45
  46   A register whose use for returning values is limited to serving as the
  47   second of a pair (for a value of type ``double``, say) need not be
  48   recognized by this macro.  So for most machines, this definition
  49   suffices:
  50
  51   .. code-block:: c++
  52
  53     #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
  54
  55   If the machine has register windows, so that the caller and the called
  56   function use different registers for the return value, this macro
  57   should recognize only the caller's register numbers.
  58
  59   This macro has been deprecated.  Use ``TARGET_FUNCTION_VALUE_REGNO_P``
  60   for a new target instead.
  61
  62 .. include:: ../tm.rst.in
  63   :start-after: [TARGET_FUNCTION_VALUE_REGNO_P]
  64   :end-before: [TARGET_FUNCTION_VALUE_REGNO_P]
  65
  66
  67 .. c:macro:: APPLY_RESULT_SIZE
  68
  69   Define this macro if :samp:`untyped_call` and :samp:`untyped_return`
  70   need more space than is implied by ``FUNCTION_VALUE_REGNO_P`` for
  71   saving and restoring an arbitrary return value.
  72
  73 .. include:: ../tm.rst.in
  74   :start-after: [TARGET_OMIT_STRUCT_RETURN_REG]
  75   :end-before: [TARGET_OMIT_STRUCT_RETURN_REG]
  76
  77
  78 .. include:: ../tm.rst.in
  79   :start-after: [TARGET_RETURN_IN_MSB]
  80   :end-before: [TARGET_RETURN_IN_MSB]