Jump threading

<h2 id="benefits">Benefits</h2>
<p>The primary benefit of jump threading is the reduction of the amount of dynamically executed jumps. This makes way for further optimizations as there is a decrease in the number of conditionals, which will improve performance. On average one can expect 2-3 instructions being omitted as a result from a successful removal of a <a href="/facts/Runtime_(program_lifecycle_phase)/lCxKsrzB">runtime</a> <a href="/facts/Branch_(computer_science)/obBGrnor">branch</a>.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a>
</p>
<h2 id="examples">Examples</h2>
<p>The following <a href="/facts/Pseudocode/XgN19duK">pseudocode</a> demonstrates when a jump may be threaded.
</p>
   10. a = SomeNumber();
   20. IF a > 10 GOTO 50
   ...
   50. IF a > 0 GOTO 100
   ...

<p>The jump on line 50 will always be taken if the jump on line 20 is taken. Therefore, for as long as line 100 is within the reachable range of the jump (or the size of the jump doesn't matter), the jump on line 20 may safely be modified to jump directly to line 100.
</p><p>Another example shows jump threading of 2 partial overlap conditions:
</p>
void baz(bool x, bool y, bool z) {
    if (x && y)
        bar();
    if (y || z)
        foo();
}

<p>The above can be transformed into:
</p>
void baz(bool x, bool y, bool z) {
    if (x && y) {
        bar();
        goto jmp;
    }
    if (y || z) {
jmp:
        foo();
    }
}

<p>If the first branch is taken, x and y are both <a href="/facts/Truth_value/SY4e2w8l">true</a> (<a href="/facts/Logical_conjunction/62uyyn1d">logical conjunction</a>), hence evaluation of <a href="/facts/Expression_(computer_science)/eRlhoBeN">expression</a> y || z is not needed (<a href="/facts/Logical_disjunction/jbI2EGlM">logical disjunction</a>). Therefore, a jump to <a href="/facts/Label_(computer_science)/DT6KU8R5">label</a> jmp is performed.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Switch_(programming)/oQCWnGWh">Switch (programming)</a></li>
<li><a href="/facts/Spaghetti_code/R6vTEHTI">Spaghetti code</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Optimize Options - Using the GNU Compiler Collection (GCC)". <a href="https://gcc.gnu.org/onlinedocs/gcc-3.4.5/gcc/Optimize-Options.html" target="_blank">https://gcc.gnu.org/onlinedocs/gcc-3.4.5/gcc/Optimize-Options.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"A gentle introduction to jump threading optimizations | Red Hat Developer". developers.redhat.com. 2019-03-13. Retrieved 2023-01-08. <a href="https://developers.redhat.com/blog/2019/03/13/intro-jump-threading-optimizations" target="_blank">https://developers.redhat.com/blog/2019/03/13/intro-jump-threading-optimizations</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"A gentle introduction to jump threading optimizations | Red Hat Developer". developers.redhat.com. 2019-03-13. Retrieved 2023-01-08. <a href="https://developers.redhat.com/blog/2019/03/13/intro-jump-threading-optimizations" target="_blank">https://developers.redhat.com/blog/2019/03/13/intro-jump-threading-optimizations</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Jump threading open-in-new

Jump threading