diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -787,6 +787,16 @@
     (void)InsertedReg;
   }
 
+  // Do not emit CSInfo for undef forwarding registers.
+  for (auto &MO : CallMI->uses()) {
+    if (!MO.isReg() || !MO.isUndef())
+      continue;
+    auto It = ForwardedRegWorklist.find(MO.getReg());
+    if (It == ForwardedRegWorklist.end())
+      continue;
+    ForwardedRegWorklist.erase(It);
+  }
+
   // We erase, from the ForwardedRegWorklist, those forwarding registers for
   // which we successfully describe a loaded value (by using
   // the describeLoadedValue()). For those remaining arguments in the working
diff --git a/llvm/test/DebugInfo/X86/dbg-call-site-undef-params.ll b/llvm/test/DebugInfo/X86/dbg-call-site-undef-params.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/dbg-call-site-undef-params.ll
@@ -0,0 +1,80 @@
+; RUN: llc -emit-call-site-info %s -filetype=obj -o - | llvm-dwarfdump - | FileCheck %s
+
+;; Compiled from source:
+;; extern int fn1 (long int x, long int y, long int z);
+;; __attribute__((noinline)) long int
+;; fn2 (long int a, long int b, long int c)
+;; {
+;;   long int q = 2 * a;
+;;   return fn1 (5, 6, 7);
+;; }
+;; int main(void) {
+;;         return fn2(14, 23, 34);
+;; }
+;; Using command:
+;; clang -g -O2 m.c -emit-llvm -S -c -o m.ll
+
+;; Verify that call site info is not created for parameters marked as "undef".
+; CHECK: DW_TAG_GNU_call_site
+; CHECK: DW_AT_abstract_origin ({{.*}} "fn2")
+; CHECK-NOT: DW_TAG_GNU_call_site_parameter
+
+; ModuleID = 'm.c'
+source_filename = "m.c"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind uwtable
+define dso_local i64 @fn2(i64 %a, i64 %b, i64 %c) local_unnamed_addr !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i64 undef, metadata !12, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i64 undef, metadata !13, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i64 undef, metadata !14, metadata !DIExpression()), !dbg !16
+  call void @llvm.dbg.value(metadata i64 undef, metadata !15, metadata !DIExpression()), !dbg !16
+  %call = tail call i32 @fn1(i64 5, i64 6, i64 7) #4, !dbg !16
+  %conv = sext i32 %call to i64, !dbg !16
+  ret i64 %conv, !dbg !16
+}
+
+declare !dbg !19 dso_local i32 @fn1(i64, i64, i64) local_unnamed_addr
+
+; Function Attrs: nounwind uwtable
+define dso_local i32 @main() local_unnamed_addr !dbg !23 {
+entry:
+  %call = tail call i64 @fn2(i64 undef, i64 undef, i64 undef), !dbg !26
+  %conv = trunc i64 %call to i32, !dbg !26
+  ret i32 %conv, !dbg !26
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 12.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "m.c", directory: "/dir")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 12.0.0"}
+!7 = distinct !DISubprogram(name: "fn2", scope: !1, file: !1, line: 4, type: !8, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10, !10, !10}
+!10 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+!11 = !{!12, !13, !14, !15}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 4, type: !10)
+!13 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !1, line: 4, type: !10)
+!14 = !DILocalVariable(name: "c", arg: 3, scope: !7, file: !1, line: 4, type: !10)
+!15 = !DILocalVariable(name: "q", scope: !7, file: !1, line: 6, type: !10)
+!16 = !DILocation(line: 0, scope: !7)
+!19 = !DISubprogram(name: "fn1", scope: !1, file: !1, line: 1, type: !20, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!20 = !DISubroutineType(types: !21)
+!21 = !{!22, !10, !10, !10}
+!22 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!23 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 9, type: !24, scopeLine: 9, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!24 = !DISubroutineType(types: !25)
+!25 = !{!22}
+!26 = !DILocation(line: 10, column: 16, scope: !23)