Index: lib/CodeGen/PrologEpilogInserter.cpp
===================================================================
--- lib/CodeGen/PrologEpilogInserter.cpp
+++ lib/CodeGen/PrologEpilogInserter.cpp
@@ -1181,6 +1181,16 @@
         MI.getOperand(0).setIsDebug();
 
         const DIExpression *DIExpr = MI.getDebugExpression();
+
+        // If we have a direct DBG_VALUE, and its complex expr is currently
+        // empty, then adding an offset will morph it into a memory location,
+        // when it is currently equivalent to a register location. This changes
+        // a pointer-valued variable to dereference that pointer, which is
+        // incorrect.
+        unsigned PrependFlags = DIExpression::ApplyOffset;
+        if (!MI.isIndirectDebugValue() && DIExpr->getNumElements() == 0)
+          PrependFlags |= DIExpression::StackValue;
+
         // If we have DBG_VALUE that is indirect and has a Implicit location
         // expression need to insert a deref before prepending a Memory
         // location expression. Also after doing this we change the DBG_VALUE
@@ -1192,8 +1202,7 @@
           // Make the DBG_VALUE direct.
           MI.getOperand(1).ChangeToRegister(0, false);
         }
-        DIExpr =
-            DIExpression::prepend(DIExpr, DIExpression::ApplyOffset, Offset);
+        DIExpr = DIExpression::prepend(DIExpr, PrependFlags, Offset);
         MI.getOperand(3).setMetadata(DIExpr);
         continue;
       }
Index: test/DebugInfo/MIR/X86/prolog-epilog-indirection.mir
===================================================================
--- /dev/null
+++ test/DebugInfo/MIR/X86/prolog-epilog-indirection.mir
@@ -0,0 +1,122 @@
+# RUN: llc %s -x mir -o - -mtriple=x86_64-unknown-unknown -run-pass=prologepilog | FileCheck %s
+#
+# Check when the DBG_VALUE on a stack slot below (for var "c") has its  stack
+# slot replaced with $rsp and a complex expression, it has DW_OP_stack_value
+# added. A direct reference to the stack slot is considered to be the _address_
+# of that stack slot, wheras its contents would be an indirect DBG_VALUE.
+#
+# Check too that for the same DBG_VALUE inst, with an indirect reference to
+# the stack slot, we do _not_ get DW_OP_plus_uconst added. This expression
+# should remain indirect, referring to the contents of the stack slot.
+#
+# CHECK:      ![[VAR:[0-9]+]] = !DILocalVariable(name: "c"
+#
+# CHECK:      LEA64r $rsp
+# CHECK-NEXT: DBG_VALUE $rsp, $noreg, ![[VAR]], !DIExpression(DW_OP_plus_uconst, {{[0-9]+}}, DW_OP_stack_value)
+# CHECK-NEXT: DBG_VALUE 1834104526
+# CHECK-NEXT: MOV64mr
+# CHECK-NEXT: DBG_VALUE $rsp, 0, ![[VAR]], !DIExpression(DW_OP_plus_uconst, {{[0-9]+}})
+
+--- |
+  ; ModuleID = 'out.ll'
+  source_filename = "abc.c"
+  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-unknown-linux-gnu"
+  
+  @b = common dso_local local_unnamed_addr global i32* null, align 8, !dbg !0
+  @a = common dso_local local_unnamed_addr global i32 0, align 4, !dbg !6
+  
+  ; Function Attrs: nounwind uwtable
+  define dso_local i32 @main() local_unnamed_addr !dbg !14 {
+  entry:
+    %l_1081 = alloca i32, align 4
+    %0 = bitcast i32* %l_1081 to i8*, !dbg !20
+    call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %0), !dbg !20
+    call void @llvm.dbg.value(metadata i32 1834104526, metadata !18, metadata !DIExpression()), !dbg !21
+    call void @llvm.dbg.value(metadata i32* %l_1081, metadata !19, metadata !DIExpression()), !dbg !21
+    store i32* %l_1081, i32** @b, align 8, !dbg !22, !tbaa !23
+    store i32 9, i32* @a, align 4, !dbg !27, !tbaa !28
+    store i32 9, i32* %l_1081, align 4, !dbg !30, !tbaa !28
+    %call = call i32 (...) @optimize_me_not(), !dbg !31
+    call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %0), !dbg !32
+    ret i32 0, !dbg !32
+  }
+  
+  ; Function Attrs: argmemonly nounwind
+  declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture)
+  
+  declare dso_local i32 @optimize_me_not(...) local_unnamed_addr
+  
+  ; Function Attrs: argmemonly nounwind
+  declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture)
+  
+  ; Function Attrs: nounwind readnone speculatable
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+  
+  !llvm.dbg.cu = !{!2}
+  !llvm.module.flags = !{!10, !11, !12}
+  !llvm.ident = !{!13}
+  
+  !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+  !1 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 2, type: !9, isLocal: false, isDefinition: true)
+  !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None)
+  !3 = !DIFile(filename: "abc.c", directory: ".")
+  !4 = !{}
+  !5 = !{!6, !0}
+  !6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+  !7 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 1, type: !8, isLocal: false, isDefinition: true)
+  !8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64)
+  !10 = !{i32 2, !"Dwarf Version", i32 4}
+  !11 = !{i32 2, !"Debug Info Version", i32 3}
+  !12 = !{i32 1, !"wchar_size", i32 4}
+  !13 = !{!"clang"}
+  !14 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 3, type: !15, scopeLine: 3, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !17)
+  !15 = !DISubroutineType(types: !16)
+  !16 = !{!8}
+  !17 = !{!18, !19}
+  !18 = !DILocalVariable(name: "l_1081", scope: !14, file: !3, line: 4, type: !8)
+  !19 = !DILocalVariable(name: "c", scope: !14, file: !3, line: 5, type: !9)
+  !20 = !DILocation(line: 4, column: 3, scope: !14)
+  !21 = !DILocation(line: 0, scope: !14)
+  !22 = !DILocation(line: 6, column: 5, scope: !14)
+  !23 = !{!24, !24, i64 0}
+  !24 = !{!"any pointer", !25, i64 0}
+  !25 = !{!"omnipotent char", !26, i64 0}
+  !26 = !{!"Simple C/C++ TBAA"}
+  !27 = !DILocation(line: 7, column: 10, scope: !14)
+  !28 = !{!29, !29, i64 0}
+  !29 = !{!"int", !25, i64 0}
+  !30 = !DILocation(line: 7, column: 6, scope: !14)
+  !31 = !DILocation(line: 8, column: 3, scope: !14)
+  !32 = !DILocation(line: 9, column: 1, scope: !14)
+
+...
+---
+name:            main
+alignment:       4
+tracksRegLiveness: true
+frameInfo:       
+  maxAlignment:    4
+  hasCalls:        true
+stack:           
+  - { id: 0, name: l_1081, type: default, offset: 0, size: 4, alignment: 4, 
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.0.entry:
+    renamable $rax = LEA64r %stack.0.l_1081, 1, $noreg, 0, $noreg
+    DBG_VALUE %stack.0.l_1081, $noreg, !19, !DIExpression(), debug-location !21
+    DBG_VALUE 1834104526, $noreg, !18, !DIExpression(), debug-location !21
+    MOV64mr $rip, 1, $noreg, @b, $noreg, killed renamable $rax, debug-location !22 :: (store 8 into @b, !tbaa !23)
+    DBG_VALUE %stack.0.l_1081, 0, !19, !DIExpression(), debug-location !21
+    MOV32mi $rip, 1, $noreg, @a, $noreg, 9, debug-location !27 :: (store 4 into @a, !tbaa !28)
+    MOV32mi %stack.0.l_1081, 1, $noreg, 0, $noreg, 9, debug-location !30 :: (store 4 into %ir.l_1081, !tbaa !28)
+    ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp, debug-location !31
+    dead $eax = MOV32r0 implicit-def dead $eflags, implicit-def $al, debug-location !31
+    CALL64pcrel32 @optimize_me_not, csr_64, implicit $rsp, implicit $ssp, implicit $al, implicit-def $rsp, implicit-def $ssp, implicit-def dead $eax, debug-location !31
+    ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp, debug-location !31
+    $eax = MOV32r0 implicit-def dead $eflags, debug-location !32
+    RET 0, $eax, debug-location !32
+
+...