Index: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2897,6 +2897,7 @@
 /// block.
 static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
   assert(I->hasOneUse() && "Invariants didn't hold!");
+  BasicBlock *SrcBlock = I->getParent();
 
   // Cannot move control-flow-involving, volatile loads, vaarg, etc.
   if (isa<PHINode>(I) || I->isEHPad() || I->mayHaveSideEffects() ||
@@ -2926,10 +2927,20 @@
       if (Scan->mayWriteToMemory())
         return false;
   }
-
   BasicBlock::iterator InsertPos = DestBlock->getFirstInsertionPt();
   I->moveBefore(&*InsertPos);
   ++NumSunkInst;
+
+  // Also sink all related debug uses from the source basic block. Otherwise we
+  // get debug use before the def.
+  SmallVector<DbgInfoIntrinsic *, 1> DbgUsers;
+  findDbgUsers(DbgUsers, I);
+  for (auto *DII : DbgUsers) {
+    if (DII->getParent() == SrcBlock) {
+      DII->moveBefore(&*InsertPos);
+      DEBUG(dbgs() << "SINK: " << *DII << '\n');
+    }
+  }
   return true;
 }
 
Index: llvm/trunk/test/DebugInfo/X86/sdagsplit-1.ll
===================================================================
--- llvm/trunk/test/DebugInfo/X86/sdagsplit-1.ll
+++ llvm/trunk/test/DebugInfo/X86/sdagsplit-1.ll
@@ -25,9 +25,9 @@
 entry:
   tail call void @llvm.dbg.value(metadata i64 %a, metadata !13, metadata !16), !dbg !17
   tail call void @llvm.dbg.value(metadata i64 %b, metadata !14, metadata !16), !dbg !18
-  tail call void @llvm.dbg.value(metadata i64 %add, metadata !15, metadata !16), !dbg !19
   %cmp = icmp eq i64 %a, %b, !dbg !20
   %add = add nsw i64 %b, 1, !dbg !22
+  tail call void @llvm.dbg.value(metadata i64 %add, metadata !15, metadata !16), !dbg !19
   %retval.0 = select i1 %cmp, i64 %add, i64 0, !dbg !23
   ret i64 %retval.0, !dbg !24
 }
Index: llvm/trunk/test/Transforms/InstCombine/debuginfo_add.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/debuginfo_add.ll
+++ llvm/trunk/test/Transforms/InstCombine/debuginfo_add.ll
@@ -28,14 +28,20 @@
   tail call void @llvm.dbg.value(metadata i64 %0, metadata !25, metadata !DIExpression()), !dbg !30
   %offset.08 = add i64 %0, -4096
   tail call void @llvm.dbg.value(metadata i64 %offset.08, metadata !26, metadata !DIExpression()), !dbg !31
-  ; CHECK: call void @llvm.dbg.value(metadata i64 %0, metadata !26, metadata !DIExpression(DW_OP_constu, 4096, DW_OP_minus, DW_OP_stack_value)), !dbg !30
   tail call void @llvm.dbg.value(metadata i32 undef, metadata !23, metadata !DIExpression()), !dbg !32
   br i1 undef, label %for.end, label %for.body.lr.ph, !dbg !32
 
 for.body.lr.ph:                                   ; preds = %entry
+  ; The 'load' and the 'add' are sunken to this basic block. So let's verify that the related dbg.values are sunken as well.
+  ; The add is later eliminated, so we verify that the dbg.value is salvaged by using DW_OP_minus.
+  ; CHECK-LABEL: for.body.lr.ph:
+  ; CHECK-NEXT: %0 = load
+  ; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 %0, metadata !25, metadata !DIExpression()), !dbg !
+  ; CHECK-NEXT: call void @llvm.dbg.value(metadata i64 %0, metadata !26, metadata !DIExpression(DW_OP_constu, 4096, DW_OP_minus, DW_OP_stack_value)), !dbg !
   br label %for.body, !dbg !32
 
 for.body:                                         ; preds = %for.body.lr.ph, %for.body
+  ; CHECK-LABEL: for.body:
   %offset.010 = phi i64 [ %offset.08, %for.body.lr.ph ], [ %offset.0, %for.body ]
   %head_size.09 = phi i32 [ undef, %for.body.lr.ph ], [ %sub2, %for.body ]
   tail call void @llvm.dbg.value(metadata i32 %head_size.09, metadata !23, metadata !DIExpression()), !dbg !31
@@ -43,7 +49,7 @@
   %sub2 = add i32 %head_size.09, -4096, !dbg !37
   %offset.0 = add i64 %offset.010, -4096
   tail call void @llvm.dbg.value(metadata i64 %offset.0, metadata !26, metadata !DIExpression()), !dbg !30
-  ; CHECK: call void @llvm.dbg.value(metadata i64 %offset.010, metadata !26, metadata !DIExpression(DW_OP_constu, 4096, DW_OP_minus, DW_OP_stack_value)), !dbg !29
+  ; CHECK: call void @llvm.dbg.value(metadata i64 %offset.010, metadata !26, metadata !DIExpression(DW_OP_constu, 4096, DW_OP_minus, DW_OP_stack_value)), !dbg !
   tail call void @llvm.dbg.value(metadata i32 %sub2, metadata !23, metadata !DIExpression()), !dbg !31
   %tobool = icmp eq i32 %sub2, 0, !dbg !32
   br i1 %tobool, label %for.end, label %for.body, !dbg !32, !llvm.loop !38