[WinEH] Add a funclet layout pass

Windows EH funclets need to be contiguous.  The FuncletLayout pass will
ensure that the funclets are together and begin with a funclet entry MBB.

Differential Revision: http://reviews.llvm.org/D12943

llvm-svn: 247937

1 files changed, 97 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/FuncletLayout.cpp b/llvm/lib/CodeGen/FuncletLayout.cpp
new file mode 100644
index 00000000000..9b40a1a7558
--- /dev/null
+++ b/llvm/lib/CodeGen/FuncletLayout.cpp
@@ -0,0 +1,97 @@
+//===-- FuncletLayout.cpp - Contiguously lay out funclets -----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements basic block placement transformations which result in
+// funclets being contiguous.
+//
+//===----------------------------------------------------------------------===//
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/MapVector.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "funclet-layout"
+
+namespace {
+class FuncletLayout : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
+  FuncletLayout() : MachineFunctionPass(ID) {
+    initializeFuncletLayoutPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnMachineFunction(MachineFunction &F) override;
+};
+}
+
+static void
+collectFuncletMembers(MapVector<MachineBasicBlock *, int> &FuncletMembership,
+                      int Funclet, MachineBasicBlock *MBB) {
+  // Don't revisit blocks.
+  if (FuncletMembership.count(MBB) > 0)
+    return;
+
+  // Add this MBB to our funclet.
+  FuncletMembership[MBB] = Funclet;
+
+  bool IsReturn = false;
+  int NumTerminators = 0;
+  for (MachineInstr &MI : MBB->terminators()) {
+    IsReturn |= MI.isReturn();
+    ++NumTerminators;
+  }
+  assert((!IsReturn || NumTerminators == 1) &&
+         "Expected only one terminator when a return is present!");
+
+  // Returns are boundaries where funclet transfer can occur, don't follow
+  // successors.
+  if (IsReturn)
+    return;
+
+  for (MachineBasicBlock *SMBB : MBB->successors())
+    if (!SMBB->isEHPad())
+      collectFuncletMembers(FuncletMembership, Funclet, SMBB);
+}
+
+char FuncletLayout::ID = 0;
+char &llvm::FuncletLayoutID = FuncletLayout::ID;
+INITIALIZE_PASS(FuncletLayout, "funclet-layout",
+                "Contiguously Lay Out Funclets", false, false)
+
+bool FuncletLayout::runOnMachineFunction(MachineFunction &F) {
+  // We don't have anything to do if there aren't any EH pads.
+  if (!F.getMMI().hasEHFunclets())
+    return false;
+
+  SmallVector<MachineBasicBlock *, 16> FuncletBlocks;
+  for (MachineBasicBlock &MBB : F)
+    if (MBB.isEHFuncletEntry())
+      FuncletBlocks.push_back(&MBB);
+
+  // We don't have anything to do if there aren't any EH pads.
+  if (FuncletBlocks.empty())
+    return false;
+
+  MapVector<MachineBasicBlock *, int> FuncletMembership;
+  for (MachineBasicBlock *MBB : FuncletBlocks)
+    collectFuncletMembers(FuncletMembership, MBB->getNumber(), MBB);
+
+  for (std::pair<llvm::MachineBasicBlock *, int> &FuncletMember :
+       FuncletMembership) {
+    // Move this block to the end of the function.
+    MachineBasicBlock *MBB = FuncletMember.first;
+    MBB->moveAfter(--F.end());
+  }
+
+  // Conservatively assume we changed something.
+  return true;
+}