misched: DAG builder should not track dependencies for SSA defs.

The vast majority of virtual register definitions don't need an entry
in the DAG builder's VRegDefs set.

llvm-svn: 151136

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
index a0992c1c464..ddf445d7a94 100644
--- a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -44,7 +44,7 @@ ScheduleDAGInstrs::ScheduleDAGInstrs(MachineFunction &mf,
     LoopRegs(MLI, MDT), FirstDbgValue(0) {
   assert((IsPostRA || LIS) && "PreRA scheduling requires LiveIntervals");
   DbgValues.clear();
-  assert(!(IsPostRA && MF.getRegInfo().getNumVirtRegs()) &&
+  assert(!(IsPostRA && MRI.getNumVirtRegs()) &&
          "Virtual registers must be removed prior to PostRA scheduling");
 }
 
@@ -361,6 +361,10 @@ void ScheduleDAGInstrs::addVRegDefDeps(SUnit *SU, unsigned OperIdx) {
   const MachineInstr *MI = SU->getInstr();
   unsigned Reg = MI->getOperand(OperIdx).getReg();
 
+  // SSA defs do not have output/anti dependencies.
+  if (llvm::next(MRI.def_begin(Reg)) == MRI.def_end())
+    return;
+
   // Add output dependence to the next nearest def of this vreg.
   //
   // Unless this definition is dead, the output dependence should be