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<h4 class="section">Handling of Jump Instructions</h4>



   <p>Jump instructions are always optimized to use the smallest possible

displacements.  This is accomplished by using byte (8-bit) displacement

jumps whenever the target is sufficiently close.  If a byte displacement

is insufficient a long displacement is used.  We do not support

word (16-bit) displacement jumps in 32-bit mode (i.e. prefixing the jump

instruction with the <code>data16</code> instruction prefix), since the 80386

insists upon masking <code>%eip</code> to 16 bits after the word displacement

is added. (See also see <a href="i386-Arch.html#i386-Arch">i386-Arch</a>)



   <p>Note that the <code>jcxz</code>, <code>jecxz</code>, <code>loop</code>, <code>loopz</code>,

<code>loope</code>, <code>loopnz</code> and <code>loopne</code> instructions only come in byte

displacements, so that if you use these instructions (<code>gcc</code> does

not use them) you may get an error message (and incorrect code).  The AT&amp;T

80386 assembler tries to get around this problem by expanding <code>jcxz foo</code>

to



<pre class="smallexample">              jcxz cx_zero

              jmp cx_nonzero

     cx_zero: jmp foo

     cx_nonzero:

     </pre>



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