CodeGen support for x86_64 SEH catch handlers in LLVM

This adds handling for ExceptionHandling::MSVC, used by the
x86_64-pc-windows-msvc triple. It assumes that filter functions have
already been outlined in either the frontend or the backend. Filter
functions are used in place of the landingpad catch clause type info
operands. In catch clause order, the first filter to return true will
catch the exception.

The C specific handler table expects the landing pad to be split into
one block per handler, but LLVM IR uses a single landing pad for all
possible unwind actions. This patch papers over the mismatch by
synthesizing single instruction BBs for every catch clause to fill in
the EH selector that the landing pad block expects.

Missing functionality:
- Accessing data in the parent frame from outlined filters
- Cleanups (from __finally) are unsupported, as they will require
  outlining and parent frame access
- Filter clauses are unsupported, as there's no clear analogue in SEH

In other words, this is the minimal set of changes needed to write IR to
catch arbitrary exceptions and resume normal execution.

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D6300

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225904 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineModuleInfo.h

@@ -66,6 +66,7 @@ struct LandingPadInfo {
   MachineBasicBlock *LandingPadBlock;    // Landing pad block.
   SmallVector<MCSymbol*, 1> BeginLabels; // Labels prior to invoke.
   SmallVector<MCSymbol*, 1> EndLabels;   // Labels after invoke.
+  SmallVector<MCSymbol*, 1> ClauseLabels; // Labels for each clause.
   MCSymbol *LandingPadLabel;             // Label at beginning of landing pad.
   const Function *Personality;           // Personality function.
   std::vector<int> TypeIds;              // List of type ids (filters negative)
@@ -330,6 +331,11 @@ public:
   ///
   void addCleanup(MachineBasicBlock *LandingPad);
 
+  /// Add a clause for a landing pad. Returns a new label for the clause. This
+  /// is used by EH schemes that have more than one landing pad. In this case,
+  /// each clause gets its own basic block.
+  MCSymbol *addClauseForLandingPad(MachineBasicBlock *LandingPad);
+
   /// getTypeIDFor - Return the type id for the specified typeinfo.  This is
   /// function wide.
   unsigned getTypeIDFor(const GlobalValue *TI);