[IR] Reformulate LLVM's EH funclet IR

While we have successfully implemented a funclet-oriented EH scheme on
top of LLVM IR, our scheme has some notable deficiencies:
- catchendpad and cleanupendpad are necessary in the current design
  but they are difficult to explain to others, even to seasoned LLVM
  experts.
- catchendpad and cleanupendpad are optimization barriers.  They cannot
  be split and force all potentially throwing call-sites to be invokes.
  This has a noticable effect on the quality of our code generation.
- catchpad, while similar in some aspects to invoke, is fairly awkward.
  It is unsplittable, starts a funclet, and has control flow to other
  funclets.
- The nesting relationship between funclets is currently a property of
  control flow edges.  Because of this, we are forced to carefully
  analyze the flow graph to see if there might potentially exist illegal
  nesting among funclets.  While we have logic to clone funclets when
  they are illegally nested, it would be nicer if we had a
  representation which forbade them upfront.

Let's clean this up a bit by doing the following:
- Instead, make catchpad more like cleanuppad and landingpad: no control
  flow, just a bunch of simple operands;  catchpad would be splittable.
- Introduce catchswitch, a control flow instruction designed to model
  the constraints of funclet oriented EH.
- Make funclet scoping explicit by having funclet instructions consume
  the token produced by the funclet which contains them.
- Remove catchendpad and cleanupendpad.  Their presence can be inferred
  implicitly using coloring information.

N.B.  The state numbering code for the CLR has been updated but the
veracity of it's output cannot be spoken for.  An expert should take a
look to make sure the results are reasonable.

Reviewers: rnk, JosephTremoulet, andrew.w.kaylor

Differential Revision: http://reviews.llvm.org/D15139

llvm-svn: 255422

1 files changed, 9 insertions, 19 deletions

diff --git a/llvm/lib/IR/Dominators.cpp b/llvm/lib/IR/Dominators.cpp
index d94e31d4875..b9d4fb7de88 100644
--- a/llvm/lib/IR/Dominators.cpp
+++ b/llvm/lib/IR/Dominators.cpp
@@ -91,11 +91,11 @@ bool DominatorTree::dominates(const Instruction *Def,
   if (Def == User)
     return false;
 
-  // The value defined by an invoke/catchpad dominates an instruction only if
-  // it dominates every instruction in UseBB.
-  // A PHI is dominated only if the instruction dominates every possible use
-  // in the UseBB.
-  if (isa<InvokeInst>(Def) || isa<CatchPadInst>(Def) || isa<PHINode>(User))
+  // The value defined by an invoke dominates an instruction only if it
+  // dominates every instruction in UseBB.
+  // A PHI is dominated only if the instruction dominates every possible use in
+  // the UseBB.
+  if (isa<InvokeInst>(Def) || isa<PHINode>(User))
     return dominates(Def, UseBB);
 
   if (DefBB != UseBB)
@@ -126,18 +126,13 @@ bool DominatorTree::dominates(const Instruction *Def,
   if (DefBB == UseBB)
     return false;
 
-  // Invoke/CatchPad results are only usable in the normal destination, not in
-  // the exceptional destination.
+  // Invoke results are only usable in the normal destination, not in the
+  // exceptional destination.
   if (const auto *II = dyn_cast<InvokeInst>(Def)) {
     BasicBlock *NormalDest = II->getNormalDest();
     BasicBlockEdge E(DefBB, NormalDest);
     return dominates(E, UseBB);
   }
-  if (const auto *CPI = dyn_cast<CatchPadInst>(Def)) {
-    BasicBlock *NormalDest = CPI->getNormalDest();
-    BasicBlockEdge E(DefBB, NormalDest);
-    return dominates(E, UseBB);
-  }
 
   return dominates(DefBB, UseBB);
 }
@@ -239,8 +234,8 @@ bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
   if (!isReachableFromEntry(DefBB))
     return false;
 
-  // Invoke/CatchPad instructions define their return values on the edges
-  // to their normal successors, so we have to handle them specially.
+  // Invoke instructions define their return values on the edges to their normal
+  // successors, so we have to handle them specially.
   // Among other things, this means they don't dominate anything in
   // their own block, except possibly a phi, so we don't need to
   // walk the block in any case.
@@ -249,11 +244,6 @@ bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
     BasicBlockEdge E(DefBB, NormalDest);
     return dominates(E, U);
   }
-  if (const auto *CPI = dyn_cast<CatchPadInst>(Def)) {
-    BasicBlock *NormalDest = CPI->getNormalDest();
-    BasicBlockEdge E(DefBB, NormalDest);
-    return dominates(E, U);
-  }
 
   // If the def and use are in different blocks, do a simple CFG dominator
   // tree query.