When isel is emitting instructions for an x86 target without CMOV, the CFG is

edited during emission.

If the basic block ends in a switch that gets lowered to a jump table, any
phis at the default edge were getting updated wrong. The jump table data
structure keeps a pointer to the header blocks that wasn't getting updated
after the MBB is split.

This bug was exposed on 32-bit Linux when disabling critical edge splitting in
codegen prepare.

The fix is to uipdate stale MBB pointers whenever a block is split during
emission.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115191 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 24 insertions, 1 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index c316ef6c54..adc225b94b 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2207,6 +2207,19 @@ size_t SelectionDAGBuilder::Clusterify(CaseVector& Cases,
   return numCmps;
 }
 
+void SelectionDAGBuilder::UpdateSplitBlock(MachineBasicBlock *First,
+                                           MachineBasicBlock *Last) {
+  // Update JTCases.
+  for (unsigned i = 0, e = JTCases.size(); i != e; ++i)
+    if (JTCases[i].first.HeaderBB == First)
+      JTCases[i].first.HeaderBB = Last;
+
+  // Update BitTestCases.
+  for (unsigned i = 0, e = BitTestCases.size(); i != e; ++i)
+    if (BitTestCases[i].Parent == First)
+      BitTestCases[i].Parent = Last;
+}
+
 void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) {
   MachineBasicBlock *SwitchMBB = FuncInfo.MBB;
 
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index 5f400e9c83..dfd1df75f1 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -398,6 +398,10 @@ public:
   void LowerCallTo(ImmutableCallSite CS, SDValue Callee, bool IsTailCall,
                    MachineBasicBlock *LandingPad = NULL);
 
+  /// UpdateSplitBlock - When an MBB was split during scheduling, update the
+  /// references that ned to refer to the last resulting block.
+  void UpdateSplitBlock(MachineBasicBlock *First, MachineBasicBlock *Last);
+
 private:
   // Terminator instructions.
   void visitRet(const ReturnInst &I);
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 63ba1c415a..450b7eff6c 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -564,13 +564,19 @@ void SelectionDAGISel::CodeGenAndEmitDAG() {
 
   // Emit machine code to BB.  This can change 'BB' to the last block being
   // inserted into.
+  MachineBasicBlock *FirstMBB = FuncInfo->MBB, *LastMBB;
   {
     NamedRegionTimer T("Instruction Creation", GroupName, TimePassesIsEnabled);
 
-    FuncInfo->MBB = Scheduler->EmitSchedule();
+    LastMBB = FuncInfo->MBB = Scheduler->EmitSchedule();
     FuncInfo->InsertPt = Scheduler->InsertPos;
   }
 
+  // If the block was split, make sure we update any references that are used to
+  // update PHI nodes later on.
+  if (FirstMBB != LastMBB)
+    SDB->UpdateSplitBlock(FirstMBB, LastMBB);
+
   // Free the scheduler state.
   {
     NamedRegionTimer T("Instruction Scheduling Cleanup", GroupName,