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-rw-r--r-- | docs/CodeGenerator.html | 45 | ||||
-rw-r--r-- | docs/LangRef.html | 7 | ||||
-rw-r--r-- | test/CodeGen/X86/sibcall.ll (renamed from test/CodeGen/X86/tailcall2.ll) | 0 |
3 files changed, 50 insertions, 2 deletions
diff --git a/docs/CodeGenerator.html b/docs/CodeGenerator.html index 2be31851e3..f26d0abfad 100644 --- a/docs/CodeGenerator.html +++ b/docs/CodeGenerator.html @@ -86,6 +86,7 @@ <li><a href="#targetimpls">Target-specific Implementation Notes</a> <ul> <li><a href="#tailcallopt">Tail call optimization</a></li> + <li><a href="#sibcallopt">Sibling call optimization</a></li> <li><a href="#x86">The X86 backend</a></li> <li><a href="#ppc">The PowerPC backend</a> <ul> @@ -1734,6 +1735,50 @@ define fastcc i32 @tailcaller(i32 %in1, i32 %in2) { </div> <!-- ======================================================================= --> <div class="doc_subsection"> + <a name="sibcallopt">Sibling call optimization</a> +</div> + +<div class="doc_text"> + +<p>Sibling call optimization is a restricted form of tail call optimization. + Unlike tail call optimization described in the previous section, it can be + performed automatically on any tail calls when <tt>-tailcallopt</tt> option + is not specified.</p> + +<p>Sibling call optimization is currently performed on x86/x86-64 when the + following constraints are met:</p> + +<ul> + <li>Caller and callee have the same calling convention. It can be either + <tt>c</tt> or <tt>fastcc</tt>. + + <li>The call is a tail call - in tail position (ret immediately follows call + and ret uses value of call or is void).</li> + + <li>Caller and callee have matching return type or the callee result is not + used. + + <li>If any of the callee arguments are being passed in stack, they must be + available in caller's own incoming argument stack and the frame offsets + must be the same. +</ul> + +<p>Example:</p> +<div class="doc_code"> +<pre> +declare i32 @bar(i32, i32) + +define i32 @foo(i32 %a, i32 %b, i32 %c) { +entry: + %0 = tail call i32 @bar(i32 %a, i32 %b) + ret i32 %0 +} +</pre> +</div> + +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"> <a name="x86">The X86 backend</a> </div> diff --git a/docs/LangRef.html b/docs/LangRef.html index 7cfa05205c..eec06fcc02 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -5149,8 +5149,11 @@ Loop: ; Infinite loop that counts from 0 on up... a <a href="#i_ret"><tt>ret</tt></a> instruction. If the "tail" marker is present, the function call is eligible for tail call optimization, but <a href="CodeGenerator.html#tailcallopt">might not in fact be - optimized into a jump</a>. As of this writing, the extra requirements for - a call to actually be optimized are: + optimized into a jump</a>. The code generator may optimize calls marked + "tail" with either 1) automatic <a href="CodeGenerator.html#sibcallopt"> + sibling call optimization</a> when the caller and callee have + matching signatures, or 2) forced tail call optimization when the + following extra requirements are met: <ul> <li>Caller and callee both have the calling convention <tt>fastcc</tt>.</li> diff --git a/test/CodeGen/X86/tailcall2.ll b/test/CodeGen/X86/sibcall.ll index 90315fd2f2..90315fd2f2 100644 --- a/test/CodeGen/X86/tailcall2.ll +++ b/test/CodeGen/X86/sibcall.ll |