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.

llvm-svn: 115191

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 63ba1c415ae..450b7eff6c9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/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,