1 files changed, 20 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyDebugFixup.cpp b/contrib/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyDebugFixup.cpp
index e06e359fc592..9a6acd157a74 100644
--- a/contrib/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyDebugFixup.cpp
+++ b/contrib/llvm-project/llvm/lib/Target/WebAssembly/WebAssemblyDebugFixup.cpp
@@ -59,6 +59,24 @@ FunctionPass *llvm::createWebAssemblyDebugFixup() {
   return new WebAssemblyDebugFixup();
 }
 
+// At this very end of the compilation pipeline, if any DBG_VALUEs with
+// registers remain, it means they are dangling info which we failed to update
+// when their corresponding def instruction was transformed/moved/splitted etc.
+// Because Wasm cannot access values in LLVM virtual registers in the debugger,
+// these dangling DBG_VALUEs in effect kill the effect of any previous DBG_VALUE
+// associated with the variable, which will appear as "optimized out".
+static void nullifyDanglingDebugValues(MachineBasicBlock &MBB,
+                                       const TargetInstrInfo *TII) {
+  for (auto &MI : llvm::make_early_inc_range(MBB)) {
+    if (MI.isDebugValue() && MI.getDebugOperand(0).isReg() &&
+        !MI.isUndefDebugValue()) {
+      LLVM_DEBUG(dbgs() << "Warning: dangling DBG_VALUE nullified: " << MI
+                        << "\n");
+      MI.getDebugOperand(0).setReg(Register());
+    }
+  }
+}
+
 bool WebAssemblyDebugFixup::runOnMachineFunction(MachineFunction &MF) {
   LLVM_DEBUG(dbgs() << "********** Debug Fixup **********\n"
                        "********** Function: "
@@ -135,6 +153,8 @@ bool WebAssemblyDebugFixup::runOnMachineFunction(MachineFunction &MF) {
     }
     assert(Stack.empty() &&
            "WebAssemblyDebugFixup: Stack not empty at end of basic block!");
+
+    nullifyDanglingDebugValues(MBB, TII);
   }
 
   return true;