[DebugInfo][Dexter] Incorrect DBG_VALUE after MCP dead copy instruction removal.

When MachineCopyPropagation eliminates a dead 'copy', its associated debug information becomes invalid. as the recorded register has been removed.  It causes the debugger to display wrong variable value.

Differential Revision: https://reviews.llvm.org/D52614

llvm-svn: 343445

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 092e5859a47..f30290109b7 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -2092,3 +2092,13 @@ void MachineInstr::collectDebugValues(
       DbgValues.push_back(&*DI);
   }
 }
+
+void MachineInstr::changeDebugValuesDefReg(unsigned Reg) {
+  // Collect matching debug values.
+  SmallVector<MachineInstr *, 2> DbgValues;
+  collectDebugValues(DbgValues);
+
+  // Propagate Reg to debug value instructions.
+  for (auto *DBI : DbgValues)
+    DBI->getOperand(0).setReg(Reg);
+}