[Bug c/87888] New: Behaviour of __builtin_arc_sr differs from its description in the manual.

["nbowler at draconx dot ca" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87888

            Bug ID: 87888
           Summary: Behaviour of __builtin_arc_sr differs from its
                    description in the manual.
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nbowler at draconx dot ca
  Target Milestone: ---

I happened to notice what appears to be an error in the GCC manual,
§6.59.4 ARC Built-in Functions[1]:

Built-in Function: void __builtin_arc_sr (unsigned int auxr, unsigned int val)

    The first argument, /auxv/, is the address of an auxiliary register,
    the second argument, /val/, is a compile time constant to be written
    to the register. Generates:

    sr  auxr, [val]

This function indeed generates the sr instruction with the parameters
exactly as described, e.g., __builtin_arc_sr(0x123, 0x456) generates

   sr 0x123, [0x456]

However, the description of those parameters is incorrect: the first
operand of sr is the value to be written, and the second is the address,
so the previous example stores the value 0x123 to aux address 0x456.

Also I think the note about val being a compile-time constant is an
error as well... the sr instruction does not require constants, and
gcc happily accepts non-constant values as arguments to this builtin.

I suggest the documentation of this builtin should be changed to match
its actual behaviour, perhaps something like:

Built-in Function: void __builtin_arc_sr (unsigned int val, unsigned int auxr)

    Stores /val/ to the auxiliary register with address /auxr/.  Generates:

    sr  val, [auxr]

[1]
https://gcc.gnu.org/onlinedocs/gcc-8.2.0/gcc/ARC-Built-in-Functions.html#index-_005f_005fbuiltin_005farc_005fsr