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Example of `define_insn'
========================

   Here is an actual example of an instruction pattern, for the
68000/68020.

     (define_insn "tstsi"
       [(set (cc0)
             (match_operand:SI 0 "general_operand" "rm"))]
       ""
       "*
     { if (TARGET_68020 || ! ADDRESS_REG_P (operands[0]))
         return \"tstl %0\";
       return \"cmpl #0,%0\"; }")

   This is an instruction that sets the condition codes based on the
value of a general operand.  It has no condition, so any insn whose RTL
description has the form shown may be handled according to this
pattern.  The name `tstsi' means "test a `SImode' value" and tells the
RTL generation pass that, when it is necessary to test such a value, an
insn to do so can be constructed using this pattern.

   The output control string is a piece of C code which chooses which
output template to return based on the kind of operand and the specific
type of CPU for which code is being generated.

   `"rm"' is an operand constraint.  Its meaning is explained below.