151 lines
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151 lines
9.4 KiB
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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<title>Call and Return Instructions (Guile Reference Manual)</title>
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<body lang="en">
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<div class="subsubsection-level-extent" id="Call-and-Return-Instructions">
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<div class="nav-panel">
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<p>
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Next: <a href="Function-Prologue-Instructions.html" accesskey="n" rel="next">Function Prologue Instructions</a>, Up: <a href="Instruction-Set.html" accesskey="u" rel="up">Instruction Set</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsubsection" id="Call-and-Return-Instructions-1"><span>9.3.7.1 Call and Return Instructions<a class="copiable-link" href="#Call-and-Return-Instructions-1"> ¶</a></span></h4>
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<p>As described earlier (see <a class="pxref" href="Stack-Layout.html">Stack Layout</a>), Guile’s calling convention
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is that arguments are passed and values returned on the stack.
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</p>
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<p>For calls, both in tail position and in non-tail position, we require
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that the procedure and the arguments already be shuffled into place
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before the call instruction. “Into place” for a tail call means that
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the procedure should be in slot 0, relative to the <code class="code">fp</code>, and the
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arguments should follow. For a non-tail call, if the procedure is in
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<code class="code">fp</code>-relative slot <var class="var">n</var>, the arguments should follow from slot
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<var class="var">n</var>+1, and there should be three free slots between <var class="var">n</var>-1 and
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<var class="var">n</var>-3 in which to save the mRA, vRA, and <code class="code">fp</code>.
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</p>
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<p>Returning values is similar. Multiple-value returns should have values
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already shuffled down to start from <code class="code">fp</code>-relative slot 0 before
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emitting <code class="code">return-values</code>.
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</p>
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<p>In both calls and returns, the <code class="code">sp</code> is used to indicate to the
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callee or caller the number of arguments or return values, respectively.
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After receiving return values, it is the caller’s responsibility to
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<em class="dfn">restore the frame</em> by resetting the <code class="code">sp</code> to its former value.
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-call-1"><span class="category-def">Instruction: </span><span><strong class="def-name">call</strong> <code class="def-code-arguments">f24:<var class="var">proc</var> x8:<var class="var">_</var> c24:<var class="var">nlocals</var></code><a class="copiable-link" href="#index-call-1"> ¶</a></span></dt>
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<dd><p>Call a procedure. <var class="var">proc</var> is the local corresponding to a procedure.
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The three values below <var class="var">proc</var> will be overwritten by the saved call
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frame data. The new frame will have space for <var class="var">nlocals</var> locals: one
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for the procedure, and the rest for the arguments which should already
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have been pushed on.
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</p>
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<p>When the call returns, execution proceeds with the next instruction.
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There may be any number of values on the return stack; the precise
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number can be had by subtracting the address of <var class="var">proc</var>-1 from the
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post-call <code class="code">sp</code>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-call_002dlabel"><span class="category-def">Instruction: </span><span><strong class="def-name">call-label</strong> <code class="def-code-arguments">f24:<var class="var">proc</var> x8:<var class="var">_</var> c24:<var class="var">nlocals</var> l32:<var class="var">label</var></code><a class="copiable-link" href="#index-call_002dlabel"> ¶</a></span></dt>
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<dd><p>Call a procedure in the same compilation unit.
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</p>
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<p>This instruction is just like <code class="code">call</code>, except that instead of
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dereferencing <var class="var">proc</var> to find the call target, the call target is
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known to be at <var class="var">label</var>, a signed 32-bit offset in 32-bit units from
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the current <code class="code">ip</code>. Since <var class="var">proc</var> is not dereferenced, it may be
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some other representation of the closure.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-tail_002dcall"><span class="category-def">Instruction: </span><span><strong class="def-name">tail-call</strong> <code class="def-code-arguments">x24:<var class="var">_</var></code><a class="copiable-link" href="#index-tail_002dcall"> ¶</a></span></dt>
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<dd><p>Tail-call a procedure. Requires that the procedure and all of the
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arguments have already been shuffled into position, and that the frame
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has already been reset to the number of arguments to the call.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-tail_002dcall_002dlabel"><span class="category-def">Instruction: </span><span><strong class="def-name">tail-call-label</strong> <code class="def-code-arguments">x24:<var class="var">_</var> l32:<var class="var">label</var></code><a class="copiable-link" href="#index-tail_002dcall_002dlabel"> ¶</a></span></dt>
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<dd><p>Tail-call a known procedure. As <code class="code">call</code> is to <code class="code">call-label</code>,
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<code class="code">tail-call</code> is to <code class="code">tail-call-label</code>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-return_002dvalues"><span class="category-def">Instruction: </span><span><strong class="def-name">return-values</strong> <code class="def-code-arguments">x24:<var class="var">_</var></code><a class="copiable-link" href="#index-return_002dvalues"> ¶</a></span></dt>
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<dd><p>Return a number of values from a call frame. The return values should
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have already been shuffled down to a contiguous array starting at slot
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0, and the frame already reset.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-receive-2"><span class="category-def">Instruction: </span><span><strong class="def-name">receive</strong> <code class="def-code-arguments">f12:<var class="var">dst</var> f12:<var class="var">proc</var> x8:<var class="var">_</var> c24:<var class="var">nlocals</var></code><a class="copiable-link" href="#index-receive-2"> ¶</a></span></dt>
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<dd><p>Receive a single return value from a call whose procedure was in
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<var class="var">proc</var>, asserting that the call actually returned at least one
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value. Afterwards, resets the frame to <var class="var">nlocals</var> locals.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-receive_002dvalues"><span class="category-def">Instruction: </span><span><strong class="def-name">receive-values</strong> <code class="def-code-arguments">f24:<var class="var">proc</var> b1:<var class="var">allow-extra?</var> x7:<var class="var">_</var> c24:<var class="var">nvalues</var></code><a class="copiable-link" href="#index-receive_002dvalues"> ¶</a></span></dt>
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<dd><p>Receive a return of multiple values from a call whose procedure was in
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<var class="var">proc</var>. If fewer than <var class="var">nvalues</var> values were returned, signal an
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error. Unless <var class="var">allow-extra?</var> is true, require that the number of
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return values equals <var class="var">nvalues</var> exactly. After <code class="code">receive-values</code>
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has run, the values can be copied down via <code class="code">mov</code>, or used in place.
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</p></dd></dl>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Function-Prologue-Instructions.html">Function Prologue Instructions</a>, Up: <a href="Instruction-Set.html">Instruction Set</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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