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Next: <a href="Discriminating-Functions.html#Discriminating-Functions" accesskey="n" rel="next">Discriminating Functions</a>, Previous: <a href="Build.html#Build" accesskey="p" rel="prev">Build</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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<h2 class="chapter">2 Calling Convention</h2>
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<p>The calling convention used within Lisp code on SBCL/x86 was, for the
longest time, really bad. If it weren’t for the fact that it predates
modern x86 CPUs, one might almost believe it to have been designed
explicitly to defeat the branch-prediction hardware therein. This
chapter is somewhat of a brain-dump of information that might be
useful when attempting to improve the situation further, mostly
written immediately after having made a dent in the problem.
</p>
<p>Assumptions about the calling convention are embedded throughout the
system. The runtime knows how to call in to Lisp and receive a value
from Lisp, the assembly-routines have intimate knowledge of what
registers are involved in a call situation,
<samp>src/compiler/target/call.lisp</samp> contains the VOPs involved in
implementing function call/return, and
<samp>src/compiler/ir2tran.lisp</samp> has assumptions about frame
allocation and argument/return-value passing locations.
</p>
<p>Note that most of this documentation also applies to other CPUs,
modulo the actual registers involved, the displacement used in the
single-value return convention, and the fact that they use the “old”
convention anywhere it is mentioned.
</p>
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