[FastISel] Undo phi node updates when falling-back to SelectionDAG.

The included test case would fail, because the MI PHI node would have two
operands from the same predecessor.

This problem occurs when a switch instruction couldn't be selected. This happens
always, because there is no default switch support for FastISel to begin with.

The problem was that FastISel would first add the operand to the PHI nodes and
then fall-back to SelectionDAG, which would then in turn add the same operands
to the PHI nodes again.

This fix removes these duplicate PHI node operands by reseting the
PHINodesToUpdate to its original state before FastISel tried to select the
instruction.

This fixes <rdar://problem/18155224>.

llvm-svn: 216640

1 files changed, 7 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index 1896c67d177..cd58c55cee8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1370,6 +1370,9 @@ FastISel::SelectInstruction(const Instruction *I) {
     removeDeadCode(FuncInfo.InsertPt, SavedInsertPt);
 
   DbgLoc = DebugLoc();
+  // Undo phi node updates, because they will be added again by SelectionDAG.
+  if (isa<TerminatorInst>(I))
+    FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
   return false;
 }
 
@@ -2004,7 +2007,7 @@ bool FastISel::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
   const TerminatorInst *TI = LLVMBB->getTerminator();
 
   SmallPtrSet<MachineBasicBlock *, 4> SuccsHandled;
-  unsigned OrigNumPHINodesToUpdate = FuncInfo.PHINodesToUpdate.size();
+  FuncInfo.OrigNumPHINodesToUpdate = FuncInfo.PHINodesToUpdate.size();
 
   // Check successor nodes' PHI nodes that expect a constant to be available
   // from this block.
@@ -2040,7 +2043,7 @@ bool FastISel::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
         if (VT == MVT::i1 || VT == MVT::i8 || VT == MVT::i16)
           VT = TLI.getTypeToTransformTo(LLVMBB->getContext(), VT);
         else {
-          FuncInfo.PHINodesToUpdate.resize(OrigNumPHINodesToUpdate);
+          FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
           return false;
         }
       }
@@ -2054,8 +2057,8 @@ bool FastISel::HandlePHINodesInSuccessorBlocks(const BasicBlock *LLVMBB) {
         DbgLoc = Inst->getDebugLoc();
 
       unsigned Reg = getRegForValue(PHIOp);
-      if (Reg == 0) {
-        FuncInfo.PHINodesToUpdate.resize(OrigNumPHINodesToUpdate);
+      if (!Reg) {
+        FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
         return false;
       }
       FuncInfo.PHINodesToUpdate.push_back(std::make_pair(MBBI++, Reg));