[DebugInfo] Don't emit incorrect descriptions of thunk params (PR42627)

The `this` parameter of a thunk requires adjustment. Stop emitting an
incorrect dbg.declare pointing to the unadjusted pointer.

We could describe the adjusted value instead, but there may not be much
benefit in doing so as users tend not to debug thunks.

Robert O'Callahan reports that this matches gcc's behavior.

Fixes PR42627.

Differential Revision: https://reviews.llvm.org/D65035

llvm-svn: 367269

1 files changed, 3 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 6ad43cefc4d..c6c2ff57e1c 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -2496,10 +2496,11 @@ void CodeGenFunction::EmitParmDecl(const VarDecl &D, ParamValue Arg,
 
   setAddrOfLocalVar(&D, DeclPtr);
 
-  // Emit debug info for param declaration.
+  // Emit debug info for param declarations in non-thunk functions.
   if (CGDebugInfo *DI = getDebugInfo()) {
     if (CGM.getCodeGenOpts().getDebugInfo() >=
-        codegenoptions::LimitedDebugInfo) {
+            codegenoptions::LimitedDebugInfo &&
+        !CurFuncIsThunk) {
       DI->EmitDeclareOfArgVariable(&D, DeclPtr.getPointer(), ArgNo, Builder);
     }
   }