Re-commit r235560: Switch lowering: extract jump tables and bit tests before building binary tree (PR22262)

Third time's the charm. The previous commit was reverted as a
reverse for-loop in SelectionDAGBuilder::lowerWorkItem did 'I--'
on an iterator at the beginning of a vector, causing asserts
when using debugging iterators. This commit fixes that.

llvm-svn: 235608

1 files changed, 7 insertions, 27 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index ddd4b28bf0c..f3735cb5315 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1413,21 +1413,15 @@ SelectionDAGISel::FinishBasicBlock() {
                  << FuncInfo->PHINodesToUpdate[i].first
                  << ", " << FuncInfo->PHINodesToUpdate[i].second << ")\n");
 
-  const bool MustUpdatePHINodes = SDB->SwitchCases.empty() &&
-                                  SDB->JTCases.empty() &&
-                                  SDB->BitTestCases.empty();
-
   // Next, now that we know what the last MBB the LLVM BB expanded is, update
   // PHI nodes in successors.
-  if (MustUpdatePHINodes) {
-    for (unsigned i = 0, e = FuncInfo->PHINodesToUpdate.size(); i != e; ++i) {
-      MachineInstrBuilder PHI(*MF, FuncInfo->PHINodesToUpdate[i].first);
-      assert(PHI->isPHI() &&
-             "This is not a machine PHI node that we are updating!");
-      if (!FuncInfo->MBB->isSuccessor(PHI->getParent()))
-        continue;
-      PHI.addReg(FuncInfo->PHINodesToUpdate[i].second).addMBB(FuncInfo->MBB);
-    }
+  for (unsigned i = 0, e = FuncInfo->PHINodesToUpdate.size(); i != e; ++i) {
+    MachineInstrBuilder PHI(*MF, FuncInfo->PHINodesToUpdate[i].first);
+    assert(PHI->isPHI() &&
+           "This is not a machine PHI node that we are updating!");
+    if (!FuncInfo->MBB->isSuccessor(PHI->getParent()))
+      continue;
+    PHI.addReg(FuncInfo->PHINodesToUpdate[i].second).addMBB(FuncInfo->MBB);
   }
 
   // Handle stack protector.
@@ -1472,10 +1466,6 @@ SelectionDAGISel::FinishBasicBlock() {
     SDB->SPDescriptor.resetPerBBState();
   }
 
-  // If we updated PHI Nodes, return early.
-  if (MustUpdatePHINodes)
-    return;
-
   for (unsigned i = 0, e = SDB->BitTestCases.size(); i != e; ++i) {
     // Lower header first, if it wasn't already lowered
     if (!SDB->BitTestCases[i].Emitted) {
@@ -1589,16 +1579,6 @@ SelectionDAGISel::FinishBasicBlock() {
   }
   SDB->JTCases.clear();
 
-  // If the switch block involved a branch to one of the actual successors, we
-  // need to update PHI nodes in that block.
-  for (unsigned i = 0, e = FuncInfo->PHINodesToUpdate.size(); i != e; ++i) {
-    MachineInstrBuilder PHI(*MF, FuncInfo->PHINodesToUpdate[i].first);
-    assert(PHI->isPHI() &&
-           "This is not a machine PHI node that we are updating!");
-    if (FuncInfo->MBB->isSuccessor(PHI->getParent()))
-      PHI.addReg(FuncInfo->PHINodesToUpdate[i].second).addMBB(FuncInfo->MBB);
-  }
-
   // If we generated any switch lowering information, build and codegen any
   // additional DAGs necessary.
   for (unsigned i = 0, e = SDB->SwitchCases.size(); i != e; ++i) {