diff options
| -rw-r--r-- | docs/ExceptionHandling.html | 86 | ||||
| -rw-r--r-- | include/llvm/CodeGen/MachineModuleInfo.h | 5 | ||||
| -rw-r--r-- | lib/CodeGen/MachineModuleInfo.cpp | 7 | ||||
| -rw-r--r-- | lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp | 18 |
4 files changed, 85 insertions, 31 deletions
diff --git a/docs/ExceptionHandling.html b/docs/ExceptionHandling.html index d49a285..eb3c5a2 100644 --- a/docs/ExceptionHandling.html +++ b/docs/ExceptionHandling.html @@ -22,8 +22,9 @@ <ol> <li><a href="#throw">Throw</a></li> <li><a href="#try_catch">Try/Catch</a></li> - <li><a href="#finallys">Finallys</a></li> + <li><a href="#cleanups">Cleanups</a></li> <li><a href="#throw_filters">Throw Filters</a></li> + <li><a href="#restrictions">Restrictions</a></li> </ol></li> <li><a href="#format_common_intrinsics">Exception Handling Intrinsics</a> <ol> @@ -212,17 +213,19 @@ further use in the landing pad and catch code.</p> three arguments. The first argument is the reference to the exception structure. The second argument is a reference to the personality function to be used for this try catch sequence. Each of the remaining arguments is either a -reference to the type info for a catch statement, or a non-negative integer -followed by that many type info references, representing a -<a href="#throw_filters">filter</a>. +reference to the type info for a catch statement, +a <a href="#throw_filters">filter</a> expression, +or the number zero representing a <a href="#cleanups">cleanup</a>. The exception is tested against the arguments sequentially from first to last. -The <i>catch all</i> (...) is represented with a <tt>null i8*</tt>. The result -of the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> is a positive -number if the exception matched a type info, a negative number if it matched a -filter, and zero if it didn't match anything. If a type info matched then the -returned value is the index of the type info in the exception table. -The LLVM C++ front end generates code to save this value in an alloca location -for further use in the landing pad and catch code.</p> +The result of the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> is a +positive number if the exception matched a type info, a negative number if it matched +a filter, and zero if it matched a cleanup. If nothing is matched, the behaviour of +the program is <a href="#restrictions">undefined</a>. +The LLVM C++ front end generates code to save the selector value in an alloca +location for further use in the landing pad and catch code. +If a type info matched then the selector value is the index of the type info in +the exception table, which can be obtained using the +<a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a> intrinsic.</p> <p>Once the landing pad has the type info selector, the code branches to the code for the first catch. The catch then checks the value of the type info @@ -249,7 +252,7 @@ replace this call with a <tt>__cxa_rethrow</tt>.</p> <!-- ======================================================================= --> <div class="doc_subsection"> - <a name="finallys">Finallys</a> + <a name="cleanups">Cleanups</a> </div> <div class="doc_text"> @@ -258,7 +261,12 @@ replace this call with a <tt>__cxa_rethrow</tt>.</p> from a landing pad to the first catch. Control may actually flow from the landing pad to clean up code and then to the first catch. Since the required clean up for each invoke in a try may be different (ex., intervening -constructor), there may be several landing pads for a given try.</p> +constructor), there may be several landing pads for a given try. If cleanups +need to be run, the number zero should be passed as the last +<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument. +However for C++ a <tt>null i8*</tt> <a href="#restrictions">must</a> be passed +instead. +</p> </div> @@ -273,8 +281,8 @@ constructor), there may be several landing pads for a given try.</p> a function. To represent this a top level landing pad may exist to filter out invalid types. To express this in LLVM code the landing pad will call <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a>. The arguments are the -number of different type infos the function may throw, followed by the type -infos themselves. +length of the filter expression (the number of type infos plus one), followed by +the type infos themselves. <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> will return a negative value if the exception does not match any of the type infos. If no match is found then a call to <tt>__cxa_call_unexpected</tt> should be made, otherwise @@ -284,6 +292,34 @@ exception structure.</p> </div> <!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="restrictions">Restrictions</a> +</div> + +<div class="doc_text"> + +<p>The semantics of the invoke instruction require that any exception that +unwinds through an invoke call should result in a branch to the invoke's unwind +label. However such a branch will only happen if the +<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> matches. +Thus in order to ensure correct operation, the front-end must only generate +<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> calls that are +guaranteed to always match whatever exception unwinds through the invoke. +For most languages it is enough to pass zero, indicating the presence of +a <a href="#cleanups">cleanup</a>, as the last +<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument. +However for C++ this is not sufficient, because the C++ personality function +will terminate the program if it detects that unwinding the exception only +results in matches with cleanups. For C++ a <tt>null i8*</tt> should +be passed as the last +<a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> argument instead. +This is interpreted as a catch-all by the C++ personality function, and will +always match. +</p> + +</div> + +<!-- ======================================================================= --> <div class="doc_section"> <a name="format_common_intrinsics">Exception Handling Intrinsics</a> </div> @@ -330,16 +366,18 @@ exception selector.</p> <p><a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> takes a minimum of three arguments. The first argument is the reference to the exception structure. The second argument is a reference to the personality function to be -used for this try catch sequence. Each of the remaining arguments is either a -reference to the type info for a catch statement, or a non-negative integer -followed by that many type info references, representing a -<a href="#throw_filters">filter</a>. +used for this try catch sequence. Each of the remaining arguments is either a +reference to the type info for a catch statement, +a <a href="#throw_filters">filter</a> expression, +or the number zero representing a <a href="#cleanups">cleanup</a>. The exception is tested against the arguments sequentially from first to last. -The <i>catch all</i> (...) is represented with a <tt>null i8*</tt>. The result -of the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> is a positive -number if the exception matched a type info, a negative number if it matched a -filter, and zero if it didn't match anything. If a type info matched then the -returned value is the index of the type info in the exception table.</p> +The result of the <a href="#llvm_eh_selector"><tt>llvm.eh.selector</tt></a> is a +positive number if the exception matched a type info, a negative number if it matched +a filter, and zero if it matched a cleanup. If nothing is matched, the behaviour of +the program is <a href="#restrictions">undefined</a>. +If a type info matched then the selector value is the index of the type info in +the exception table, which can be obtained using the +<a href="#llvm_eh_typeid_for"><tt>llvm.eh.typeid.for</tt></a> intrinsic.</p> </div> diff --git a/include/llvm/CodeGen/MachineModuleInfo.h b/include/llvm/CodeGen/MachineModuleInfo.h index 778b75c..bb79c19 100644 --- a/include/llvm/CodeGen/MachineModuleInfo.h +++ b/include/llvm/CodeGen/MachineModuleInfo.h @@ -966,7 +966,6 @@ struct LandingPadInfo { : LandingPadBlock(MBB) , LandingPadLabel(0) , Personality(NULL) - , TypeIds(1, 0) // Always have cleanups {} }; @@ -1239,6 +1238,10 @@ public: void addFilterTypeInfo(MachineBasicBlock *LandingPad, std::vector<GlobalVariable *> &TyInfo); + /// addCleanup - Add a cleanup action for a landing pad. + /// + void addCleanup(MachineBasicBlock *LandingPad); + /// getTypeIDFor - Return the type id for the specified typeinfo. This is /// function wide. unsigned getTypeIDFor(GlobalVariable *TI); diff --git a/lib/CodeGen/MachineModuleInfo.cpp b/lib/CodeGen/MachineModuleInfo.cpp index 77fb643..62224fd 100644 --- a/lib/CodeGen/MachineModuleInfo.cpp +++ b/lib/CodeGen/MachineModuleInfo.cpp @@ -1726,6 +1726,13 @@ void MachineModuleInfo::addFilterTypeInfo(MachineBasicBlock *LandingPad, LP.TypeIds.push_back(getFilterIDFor(IdsInFilter)); } +/// addCleanup - Add a cleanup action for a landing pad. +/// +void MachineModuleInfo::addCleanup(MachineBasicBlock *LandingPad) { + LandingPadInfo &LP = getOrCreateLandingPadInfo(LandingPad); + LP.TypeIds.push_back(0); +} + /// TidyLandingPads - Remap landing pad labels and remove any deleted landing /// pads. void MachineModuleInfo::TidyLandingPads() { diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp index 7439e61..12024ff 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp +++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp @@ -2519,7 +2519,7 @@ static void addCatchInfo(CallInst &I, MachineModuleInfo *MMI, for (unsigned i = N - 1; i > 2; --i) { if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand(i))) { unsigned FilterLength = CI->getZExtValue(); - unsigned FirstCatch = i + FilterLength + 1; + unsigned FirstCatch = i + FilterLength + !FilterLength; assert (FirstCatch <= N && "Invalid filter length"); if (FirstCatch < N) { @@ -2530,11 +2530,17 @@ static void addCatchInfo(CallInst &I, MachineModuleInfo *MMI, TyInfo.clear(); } - TyInfo.reserve(FilterLength); - for (unsigned j = i + 1; j < FirstCatch; ++j) - TyInfo.push_back(ExtractTypeInfo(I.getOperand(j))); - MMI->addFilterTypeInfo(MBB, TyInfo); - TyInfo.clear(); + if (!FilterLength) { + // Cleanup. + MMI->addCleanup(MBB); + } else { + // Filter. + TyInfo.reserve(FilterLength - 1); + for (unsigned j = i + 1; j < FirstCatch; ++j) + TyInfo.push_back(ExtractTypeInfo(I.getOperand(j))); + MMI->addFilterTypeInfo(MBB, TyInfo); + TyInfo.clear(); + } N = i; } |