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| <a name="Example-of-define_005finsn"></a> |
| <h3 class="section">16.3 Example of <code>define_insn</code></h3> |
| <a name="index-define_005finsn-example"></a> |
| |
| <p>Here is an example of an instruction pattern, taken from the machine |
| description for the 68000/68020. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(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\"; |
| }") |
| </pre></div> |
| |
| <p>This can also be written using braced strings: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(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"; |
| }) |
| </pre></div> |
| |
| <p>This describes an instruction which sets the condition codes based on the |
| value of a general operand. It has no condition, so any insn with an RTL |
| description of the form shown may be matched to this pattern. The name |
| ‘<samp>tstsi</samp>’ means “test a <code>SImode</code> 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. |
| </p> |
| <p>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. |
| </p> |
| <p>‘<samp>"rm"</samp>’ is an operand constraint. Its meaning is explained below. |
| </p> |
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