1 files changed, 15 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/ProcessImplicitDefs.cpp b/llvm/lib/CodeGen/ProcessImplicitDefs.cpp
index 2caef08b509..80121ca0f29 100644
--- a/llvm/lib/CodeGen/ProcessImplicitDefs.cpp
+++ b/llvm/lib/CodeGen/ProcessImplicitDefs.cpp
@@ -102,6 +102,21 @@ bool ProcessImplicitDefs::runOnMachineFunction(MachineFunction &fn) {
         continue;
       }
 
+      if (MI->isInsertSubreg()) {
+        MachineOperand &MO = MI->getOperand(2);
+        if (ImpDefRegs.count(MO.getReg())) {
+          // %reg1032<def> = INSERT_SUBREG %reg1032, undef, 2
+          // This is an identity copy, eliminate it now.
+          if (MO.isKill()) {
+            LiveVariables::VarInfo& vi = lv_->getVarInfo(MO.getReg());
+            vi.removeKill(MI);
+          }
+          MI->eraseFromParent();
+          Changed = true;
+          continue;
+        }
+      }
+
       // Eliminate %reg1032:sub<def> = COPY undef.
       if (MI->isCopy() && MI->getOperand(0).getSubReg()) {
         MachineOperand &MO = MI->getOperand(1);