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Diffstat (limited to 'docs/LangRef.html')
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1 files changed, 90 insertions, 4 deletions
diff --git a/docs/LangRef.html b/docs/LangRef.html index dce39c5..1c3cc89 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -202,6 +202,7 @@ <li><a href="#i_select">'<tt>select</tt>' Instruction</a></li> <li><a href="#i_call">'<tt>call</tt>' Instruction</a></li> <li><a href="#i_va_arg">'<tt>va_arg</tt>' Instruction</a></li> + <li><a href="#i_landingpad">'<tt>landingpad</tt>' Instruction</a></li> </ol> </li> </ol> @@ -3256,6 +3257,17 @@ IfUnequal: instruction, control is interrupted and continued at the dynamically nearest "exception" label.</p> +<p>The '<tt>exception</tt>' label is a + <i><a href="ExceptionHandling.html#overview">landing pad</a></i> for the + exception. As such, '<tt>exception</tt>' label is required to have the + "<a href="#i_landingpad"><tt>landingpad</tt></a>" instruction, which contains + the information about about the behavior of the program after unwinding + happens, as its first non-PHI instruction. The restrictions on the + "<tt>landingpad</tt>" instruction's tightly couples it to the + "<tt>invoke</tt>" instruction, so that the important information contained + within the "<tt>landingpad</tt>" instruction can't be lost through normal + code motion.</p> + <h5>Arguments:</h5> <p>This instruction requires several arguments:</p> @@ -3372,17 +3384,18 @@ that the invoke/unwind semantics are likely to change in future versions.</p> successors.</p> <h5>Arguments:</h5> -<p>The '<tt>resume</tt>' instruction's argument must have the same type as the - result of any '<tt>landingpad</tt>' instruction in the same function.</p> +<p>The '<tt>resume</tt>' instruction requires one argument, which must have the + same type as the result of the '<tt>landingpad</tt>' instruction which + interrupted the unwinding.</p> <h5>Semantics:</h5> <p>The '<tt>resume</tt>' instruction resumes propagation of an existing (in-flight) exception whose unwinding was interrupted with - a landingpad instruction.</p> + a <a href="#i_landingpad"><tt>landingpad</tt></a> instruction.</p> <h5>Example:</h5> <pre> - resume { i8*, i32 } %exn + resume { i8*, i32 } %exn </pre> </div> @@ -5970,6 +5983,79 @@ freestanding environments and non-C-based languages.</p> </div> +<!-- _______________________________________________________________________ --> +<h4> + <a name="i_landingpad">'<tt>landingpad</tt>' Instruction</a> +</h4> + +<div> + +<h5>Syntax:</h5> +<pre> + <resultval> = landingpad <somety> personality <type> <pers_fn> cleanup? <clause>+ + <clause> := catch <type> <value> + <clause> := filter <type> <value> +</pre> + +<h5>Overview:</h5> +<p>The '<tt>landingpad</tt>' instruction is used by + <a href="ExceptionHandling.html#overview">LLVM's exception handling + system</a> to specify that a basic block is a landing pad — one where + the exception lands, and corresponds to the code found in the + <i><tt>catch</tt></i> portion of a <i><tt>try/catch</tt></i> sequence. It + defines values supplied by the personality function (<tt>pers_fn</tt>) upon + re-entry to the function. The <tt>resultval</tt> has the + type <tt>somety</tt>.</p> + +<h5>Arguments:</h5> +<p>This instruction takes a <tt>pers_fn</tt> value. This is the personality + function associated with the unwinding mechanism. The optional + <tt>cleanup</tt> flag indicates that the landing pad block is a cleanup.</p> + +<p>A <tt>clause</tt> begins with the clause type — <tt>catch</tt> + or <tt>filter</tt> — and contains a list of global variables + representing the "types" that may be caught or filtered respectively. The + '<tt>landingpad</tt>' instruction must contain <em>at least</em> + one <tt>clause</tt> or the <tt>cleanup</tt> flag.</p> + +<h5>Semantics:</h5> +<p>The '<tt>landingpad</tt>' instruction defines the values which are set by the + personality function (<tt>pers_fn</tt>) upon re-entry to the function, and + therefore the "result type" of the <tt>landingpad</tt> instruction. As with + calling conventions, how the personality function results are represented in + LLVM IR is target specific.</p> + +<p>The <tt>landingpad</tt> instruction has several restrictions:</p> + +<ul> + <li>A landing pad block is a basic block which is the unwind destination of an + '<tt>invoke</tt>' instruction.</li> + <li>A landing pad block must have a '<tt>landingpad</tt>' instruction as its + first non-PHI instruction.</li> + <li>There can be only one '<tt>landingpad</tt>' instruction within the landing + pad block.</li> + <li>A basic block that is not a landing pad block may not include a + '<tt>landingpad</tt>' instruction.</li> + <li>All '<tt>landingpad</tt>' instructions in a function must have the same + personality function.</li> +</ul> + +<h5>Example:</h5> +<pre> + ;; A landing pad which can catch an integer. + %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 + catch i8** @_ZTIi + ;; A landing pad that is a cleanup. + %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 + cleanup + ;; A landing pad which can catch an integer and can only throw a double. + %res = landingpad { i8*, i32 } personality i32 (...)* @__gxx_personality_v0 + catch i8** @_ZTIi + filter i8** @_ZTId +</pre> + +</div> + </div> </div> |