Index: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5492,10 +5492,16 @@
       return nullptr;
     }
 
-    // The value is not used in this block yet (or it would have an SDNode).
-    // We still want the value to appear for the user if possible -- if it has
-    // an associated VReg, we can refer to that instead.
-    if (!isa<Argument>(V)) {
+    // Special rules apply for the first dbg.values of parameter variables in a
+    // function. Identify them by the fact they reference Argument Values, that
+    // they're parameters, and they are parameters of the current function. We
+    // need to let them dangle until they get an SDNode.
+    bool IsParamOfFunc = isa<Argument>(V) && Variable->isParameter() &&
+                         !DI.getDebugLoc()->getInlinedAt();
+    if (!IsParamOfFunc) {
+      // The value is not used in this block yet (or it would have an SDNode).
+      // We still want the value to appear for the user if possible -- if it has
+      // an associated VReg, we can refer to that instead.
       auto VMI = FuncInfo.ValueMap.find(V);
       if (VMI != FuncInfo.ValueMap.end()) {
         unsigned Reg = VMI->second;
Index: llvm/trunk/test/DebugInfo/X86/dbg-value-arg-movement.ll
===================================================================
--- llvm/trunk/test/DebugInfo/X86/dbg-value-arg-movement.ll
+++ llvm/trunk/test/DebugInfo/X86/dbg-value-arg-movement.ll
@@ -0,0 +1,104 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown -start-after=codegenprepare -stop-before=expand-isel-pseudos %s -o - | FileCheck %s
+
+; Test the movement of dbg.values of arguments. SelectionDAG tries to be
+; helpful and places DBG_VALUEs of Arguments at the start of functions.
+; Unfortunately, this doesn't necessarily make sense, as one can specify an
+; Argument IR Value as a variable location anywhere in the program.
+;
+; Distinguish cases where we want to hoist DBG_VALUEs, and those where we
+; don't, by whether the referred to variable is a parameter to the current
+; function. In the test below, 'xyzzy' is a parameter to an inlined function,
+; but should not be hoisted to the start of the function.
+;
+; Original test case, in which 'xyzzy' became unavailable because its DBG_VALUE
+; landed far from any uses, compiled "clang -O2 -g" with inlining,
+;
+;    int ext(void);
+;
+;    int
+;    foo(int xyzzy)
+;    {
+;      xyzzy = ext() * xyzzy;
+;      xyzzy += 1;
+;      ext();
+;      return xyzzy;
+;    }
+;
+;    int
+;    bar(int baz, int qux)
+;    {
+;      int fish;
+;      switch (qux) {
+;      case 12:        fish = 8;        break;
+;      case 848:       fish = 0;        break;
+;      case 99999:     fish = -1;       break;
+;      default:        fish = 12;
+;      }
+;      qux %= fish;
+;      qux += foo(baz);
+;      return qux;
+;    }
+
+; CHECK: [[BAZVAR:![0-9]+]] = !DILocalVariable(name: "baz",
+; CHECK: [[XYZVAR:![0-9]+]] = !DILocalVariable(name: "xyzzy",
+
+; Start of MIR function block,
+; CHECK-LABEL: body
+; Expect DBG_VALUE of physreg,
+; CHECK:       DBG_VALUE $edi, $noreg, [[BAZVAR]]
+; Expect DBG_VALUE of virtreg,
+; CHECK:       DBG_VALUE [[ARGREG:%[0-9]+]], $noreg, [[BAZVAR]]
+; Label for next block,
+; CHECK-LABEL: bb.1.next
+; Correctly place dbg.value in the 'next' block.
+; CHECK:       DBG_VALUE [[ARGREG]], $noreg, [[XYZVAR]]
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare i32 @ext()
+
+define dso_local i32 @bar(i32, i32) local_unnamed_addr !dbg !7 {
+  %3 = srem i32 %1, %0, !dbg !15
+  call void @llvm.dbg.value(metadata i32 %0, metadata !12, metadata !DIExpression()), !dbg !16
+  br label %next
+
+next:                                             ; preds = %2
+  call void @llvm.dbg.value(metadata i32 %0, metadata !17, metadata !DIExpression()), !dbg !22
+  %4 = tail call i32 @ext(), !dbg !24
+  %5 = mul nsw i32 %3, %4, !dbg !25
+  %6 = add i32 %5, %0, !dbg !25
+  ret i32 %6, !dbg !25
+}
+
+; Function Attrs: nounwind readnone speculatable
+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: "", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 8.0.0"}
+!7 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 19, type: !8, scopeLine: 20, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "baz", arg: 1, scope: !7, file: !1, line: 19, type: !10)
+!15 = !DILocation(line: 35, column: 7, scope: !7)
+!16 = !DILocation(line: 19, column: 9, scope: !7)
+!17 = !DILocalVariable(name: "xyzzy", arg: 1, scope: !18, file: !1, line: 10, type: !10)
+!18 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 10, type: !19, scopeLine: 11, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !21)
+!19 = !DISubroutineType(types: !20)
+!20 = !{!10, !10}
+!21 = !{!17}
+!22 = !DILocation(line: 10, column: 9, scope: !18, inlinedAt: !23)
+!23 = distinct !DILocation(line: 36, column: 10, scope: !7)
+!24 = !DILocation(line: 12, column: 11, scope: !18, inlinedAt: !23)
+!25 = !DILocation(line: 37, column: 3, scope: !7)