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Document the llvm.unwind intrinsic.

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Clarify the documentation for the invoke instruction

llvm-svn: 8196
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Chris Lattner 2003-08-28 22:12:25 +00:00
parent f79868b288
commit 5a9007a58b
1 changed files with 46 additions and 18 deletions
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@ -81,6 +81,7 @@
<li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
<li><a href="#i_va_end" >'<tt>llvm.va_end</tt>' Intrinsic</a>
<li><a href="#i_va_copy" >'<tt>llvm.va_copy</tt>' Intrinsic</a>
<li><a href="#i_unwind" >'<tt>llvm.unwind</tt>' Intrinsic</a>
</ol>
</ol>
@ -741,13 +742,14 @@ conditional branches, or with a lookup table.<p>
<h5>Overview:</h5>
The '<tt>invoke</tt>' instruction is used to cause control flow to transfer to a
specified function, with the possibility of control flow transfer to either the
'<tt>normal label</tt>' label or the '<tt>exception label</tt>'. The '<tt><a
href="#i_call">call</a></tt>' instruction is closely related, but guarantees
that control flow either never returns from the called function, or that it
returns to the instruction following the '<tt><a href="#i_call">call</a></tt>'
instruction.<p>
The '<tt>invoke</tt>' instruction causes control to transfer to a specified
function, with the possibility of control flow transfer to either the
'<tt>normal label</tt>' label or the '<tt>exception label</tt>'. If the callee
function invokes the "<tt><a href="#i_ret">ret</a></tt>" instruction, control
flow will return to the "normal" label. If the callee (or any indirect callees)
calls the "<a href="#i_unwind"><tt>llvm.unwind</tt></a>" intrinsic, control is
interrupted, and continued at the "except" label.<p>
<h5>Arguments:</h5>
@ -757,7 +759,7 @@ This instruction requires several arguments:<p>
<li>'<tt>ptr to function ty</tt>': shall be the signature of the pointer to
function value being invoked. In most cases, this is a direct function
invocation, but indirect <tt>invoke</tt>s are just as possible, branching off
an arbitrary pointer to function value.<p>
an arbitrary pointer to function value.
<li>'<tt>function ptr val</tt>': An LLVM value containing a pointer to a
function to be invoked.
@ -769,26 +771,26 @@ accepts a variable number of arguments, the extra arguments can be specified.
<li>'<tt>normal label</tt>': the label reached when the called function executes
a '<tt><a href="#i_ret">ret</a></tt>' instruction.
<li>'<tt>exception label</tt>': the label reached when an exception is thrown.
<li>'<tt>exception label</tt>': the label reached when a callee calls the <a
href="#i_unwind"><tt>llvm.unwind</tt></a> intrinsic.
</ol>
<h5>Semantics:</h5>
This instruction is designed to operate as a standard '<tt><a
href="#i_call">call</a></tt>' instruction in most regards. The primary
difference is that it associates a label with the function invocation that may
be accessed via the runtime library provided by the execution environment. This
instruction is used in languages with destructors to ensure that proper cleanup
is performed in the case of either a <tt>longjmp</tt> or a thrown exception.
Additionally, this is important for implementation of '<tt>catch</tt>' clauses
in high-level languages that support them.<p>
difference is that it establishes an association with a label, which is used by the runtime library to unwind the stack.<p>
<!-- For a more comprehensive explanation of how this instruction is used, look in the llvm/docs/2001-05-18-ExceptionHandling.txt document.<p> -->
This instruction is used in languages with destructors to ensure that proper
cleanup is performed in the case of either a <tt>longjmp</tt> or a thrown
exception. Additionally, this is important for implementation of
'<tt>catch</tt>' clauses in high-level languages that support them.<p>
<h5>Example:</h5>
<pre>
%retval = invoke int %Test(int 15)
to label %Continue except label %TestCleanup <i>; {int}:retval set</i>
to label %Continue
except label %TestCleanup <i>; {int}:retval set</i>
</pre>
@ -1801,6 +1803,32 @@ because the <tt><a href="i_va_begin">llvm.va_begin</a></tt> intrinsic may be
arbitrarily complex and require memory allocation, for example.<p>
<!-- _______________________________________________________________________ -->
</ul><a name="i_unwind"><h4><hr size=0>'<tt>llvm.unwind</tt>' Intrinsic</h4><ul>
<h5>Syntax:</h5>
<pre>
call void (void)* %llvm.unwind()
</pre>
<h5>Overview:</h5>
The '<tt>llvm.unwind</tt>' intrinsic unwinds the stack, continuing control flow
at the first callee in the dynamic call stack which used an <a
href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. This is
primarily used to implement exception handling.
<h5>Semantics:</h5>
The '<tt>llvm.unwind</tt>' intrinsic causes execution of the current function to
immediately halt. The dynamic call stack is then searched for the first <a
href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. Once found,
execution continues at the "exceptional" destination block specified by the
invoke instruction. If there is no <tt>invoke</tt> instruction in the dynamic
call chain, undefined behavior results.
<!-- *********************************************************************** -->
</ul>
<!-- *********************************************************************** -->
@ -1811,7 +1839,7 @@ arbitrarily complex and require memory allocation, for example.<p>
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
<!-- Created: Tue Jan 23 15:19:28 CST 2001 -->
<!-- hhmts start -->
Last modified: Mon Jul 14 12:12:22 CDT 2003
Last modified: Thu Aug 28 17:11:50 CDT 2003
<!-- hhmts end -->
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