1 files changed, 15 insertions, 6 deletions
diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 72e5870..dc4b1a6 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -1131,15 +1131,24 @@ auto MachineFunction::salvageCopySSA(MachineInstr &MI)
     }
   }
 
+  MachineBasicBlock &InsertBB = *CurInst->getParent();
+
   // We reached the start of the block before finding a defining instruction.
-  // It must be an argument: assert that this is the entry block, and produce
-  // a DBG_PHI.
-  assert(!State.first.isVirtual());
-  MachineBasicBlock &TargetBB = *CurInst->getParent();
-  assert(&*TargetBB.getParent()->begin() == &TargetBB);
+  // It could be from a constant register, otherwise it must be an argument.
+  if (TRI.isConstantPhysReg(State.first)) {
+    // We can produce a DBG_PHI that identifies the constant physreg. Doesn't
+    // matter where we put it, as it's constant valued.
+    assert(CurInst->isCopy());
+  } else {
+    // Assert that this is the entry block. If it isn't, then there is some
+    // code construct we don't recognise that deals with physregs across
+    // blocks.
+    assert(!State.first.isVirtual());
+    assert(&*InsertBB.getParent()->begin() == &InsertBB);
+  }
 
   // Create DBG_PHI for specified physreg.
-  auto Builder = BuildMI(TargetBB, TargetBB.getFirstNonPHI(), DebugLoc(),
+  auto Builder = BuildMI(InsertBB, InsertBB.getFirstNonPHI(), DebugLoc(),
                          TII.get(TargetOpcode::DBG_PHI));
   Builder.addReg(State.first, RegState::Debug);
   unsigned NewNum = getNewDebugInstrNum();