Index: include/llvm/CodeGen/FastISel.h
===================================================================
--- include/llvm/CodeGen/FastISel.h
+++ include/llvm/CodeGen/FastISel.h
@@ -226,6 +226,9 @@
   /// be appended, and clear the local CSE map.
   void startNewBlock();
 
+  /// \brief Performs post-processing of complete basic block.
+  void finishBasicBlock();
+
   /// \brief Return current debug location information.
   DebugLoc getCurDebugLoc() const { return DbgLoc; }
 
@@ -569,6 +572,11 @@
   bool lowerCallOperands(const CallInst *CI, unsigned ArgIdx, unsigned NumArgs,
                          const Value *Callee, bool ForceRetVoidTy,
                          CallLoweringInfo &CLI);
+
+  /// \brief Copies first non-empty debug location from list of instructions as
+  /// starting location for current block.
+  /// \param BlockFinished Whether whole block was processed at this point.
+  void fixupLocalValueLocations(bool BlockFinished);
 };
 
 } // end namespace llvm
Index: lib/CodeGen/SelectionDAG/FastISel.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/FastISel.cpp
+++ lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -104,6 +104,43 @@
   LastLocalValue = EmitStartPt;
 }
 
+void FastISel::finishBasicBlock() {
+  fixupLocalValueLocations(true);
+}
+
+void FastISel::fixupLocalValueLocations(bool BlockFinished) {
+  bool IsEntryBlock =
+      (FuncInfo.MBB == FuncInfo.MBBMap[&FuncInfo.Fn->getEntryBlock()]);
+
+  // If this is the wrap-up stage of block processing, and any local-value
+  // instructions are _not_ at the very beginning of the block, then we should
+  // _not_ update their debug info.
+  //
+  // Skip entry basic block to do not move "prologue_end" location above stack
+  // adjustment.
+  if (BlockFinished && (EmitStartPt || IsEntryBlock))
+    return;
+
+  // Nothing to do if we didn't emit any local values.
+  if (LocalValueMap.empty())
+    return;
+
+  // Find first local value.
+  MachineBasicBlock::iterator FirstLocalValue;
+  if (EmitStartPt) {
+    FirstLocalValue = EmitStartPt;
+    ++FirstLocalValue;
+  } else {
+    FirstLocalValue = FuncInfo.MBB->getFirstNonPHI();
+  }
+
+  // Find first instruction with non-null debug location.
+  auto InstWithLoc = std::find_if(FuncInfo.InsertPt, FuncInfo.MBB->end(),
+                                  std::mem_fn(&MachineInstr::getDebugLoc));
+  if (InstWithLoc != FuncInfo.MBB->end())
+    FirstLocalValue->setDebugLoc(InstWithLoc->getDebugLoc());
+}
+
 bool FastISel::lowerArguments() {
   if (!FuncInfo.CanLowerReturn)
     // Fallback to SDISel argument lowering code to deal with sret pointer
@@ -125,6 +162,7 @@
 }
 
 void FastISel::flushLocalValueMap() {
+  fixupLocalValueLocations(false);
   LocalValueMap.clear();
   LastLocalValue = EmitStartPt;
   recomputeInsertPt();
Index: lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1314,6 +1314,8 @@
     }
 
     FinishBasicBlock();
+    if (FastIS)
+      FastIS->finishBasicBlock();
     FuncInfo->PHINodesToUpdate.clear();
   }
 
Index: test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
===================================================================
--- test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
+++ test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
@@ -1,4 +1,5 @@
 ; RUN: llc -filetype=asm -asm-verbose=0 < %s | FileCheck %s
+; RUN: llc -fast-isel -filetype=asm -asm-verbose=0 < %s | FileCheck %s
 
 ; int main()
 ; {
Index: test/DebugInfo/X86/dbg-line-fast-isel.ll
===================================================================
--- /dev/null
+++ test/DebugInfo/X86/dbg-line-fast-isel.ll
@@ -0,0 +1,100 @@
+; RUN: llc -disable-fp-elim -O0 %s -o - | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; xx // return value generates non-empty prologue for
+; xx // isel_line_test_prologue_dbginfo
+; 01 void callme(int);
+; 02
+; 03 int isel_line_test_subblocks(int arg)
+; 04 {
+; 05   if (arg > 5000)
+; xx     // "200" should have correct location
+; 06     callme(200);
+; xx   // getting here from either of predecessors should yield correct debug
+; xx   // location for 300, so location should be inside this block
+; 07   callme(300);
+; xx   // location for "0" constant after the call in the middle of a block
+; xx   // should be correct
+; 08   return 0;
+; 09 }
+; 10
+; 11 void isel_line_test_prologue_dbginfo()
+; 12 {
+; 13   callme(400);
+; 14 }
+
+; Function Attrs: nounwind uwtable
+define i32 @isel_line_test_subblocks(i32 %arg) {
+; The start of each non-entry block (or sub-block) should get a .loc directive.
+; CHECK:       isel_line_test_subblocks:
+; CHECK:       # BB#1:
+; CHECK-NEXT:  .loc 1 6 5
+; CHECK:       LBB0_2:
+; CHECK-NEXT:  .loc 1 7 3
+; CHECK:       callq callme
+; CHECK-NEXT:  .loc 1 8 3
+
+entry:
+  %arg.addr = alloca i32, align 4
+  store i32 %arg, i32* %arg.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %arg.addr, metadata !14, metadata !15), !dbg !16
+  %0 = load i32, i32* %arg.addr, align 4, !dbg !17
+  %cmp = icmp sgt i32 %0, 5000, !dbg !19
+  br i1 %cmp, label %if.then, label %if.end, !dbg !20
+
+if.then:                                          ; preds = %entry
+  call void @callme(i32 200), !dbg !21
+  br label %if.end, !dbg !21
+
+if.end:                                           ; preds = %if.then, %entry
+  call void @callme(i32 300), !dbg !22
+  ret i32 0, !dbg !23
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+declare void @callme(i32)
+
+; Function Attrs: nounwind uwtable
+define void @isel_line_test_prologue_dbginfo() {
+; The stack adjustment should be part of the prologue.
+; CHECK: isel_line_test_prologue_dbginfo:
+; CHECK: movq %rsp, %rbp
+; CHECK: .loc 1 13 3 prologue_end
+
+entry:
+  call void @callme(i32 400), !dbg !24
+  ret void, !dbg !25
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!11, !12}
+
+!0 = !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, retainedTypes: !2, subprograms: !3, globals: !2, imports: !2)
+!1 = !DIFile(filename: "fast-isel.c", directory: "")
+!2 = !{}
+!3 = !{!4, !8}
+!4 = !DISubprogram(name: "isel_line_test_subblocks", scope: !1, file: !1, line: 3, type: !5, isLocal: false, isDefinition: true, scopeLine: 4, flags: DIFlagPrototyped, isOptimized: false, function: i32 (i32)* @isel_line_test_subblocks, variables: !2)
+!5 = !DISubroutineType(types: !6)
+!6 = !{!7, !7}
+!7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!8 = !DISubprogram(name: "isel_line_test_prologue_dbginfo", scope: !1, file: !1, line: 11, type: !9, isLocal: false, isDefinition: true, scopeLine: 12, isOptimized: false, function: void ()* @isel_line_test_prologue_dbginfo, variables: !2)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !{i32 2, !"Dwarf Version", i32 4}
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "arg", arg: 1, scope: !4, file: !1, line: 3, type: !7)
+!15 = !DIExpression()
+!16 = !DILocation(line: 3, column: 34, scope: !4)
+!17 = !DILocation(line: 5, column: 7, scope: !18)
+!18 = distinct !DILexicalBlock(scope: !4, file: !1, line: 5, column: 7)
+!19 = !DILocation(line: 5, column: 11, scope: !18)
+!20 = !DILocation(line: 5, column: 7, scope: !4)
+!21 = !DILocation(line: 6, column: 5, scope: !18)
+!22 = !DILocation(line: 7, column: 3, scope: !4)
+!23 = !DILocation(line: 8, column: 3, scope: !4)
+!24 = !DILocation(line: 13, column: 3, scope: !8)
+!25 = !DILocation(line: 14, column: 1, scope: !8)