Index: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5344,14 +5344,15 @@
       return nullptr;
     }
 
-    // PHI nodes have already been selected, so we should know which VReg that
-    // is assigns to already.
-    if (isa<PHINode>(V)) {
+    // 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)) {
       auto VMI = FuncInfo.ValueMap.find(V);
       if (VMI != FuncInfo.ValueMap.end()) {
         unsigned Reg = VMI->second;
-        // The PHI node may be split up into several MI PHI nodes (in
-        // FunctionLoweringInfo::set).
+        // If this is a PHI node, it may be split up into several MI PHI nodes
+        // (in FunctionLoweringInfo::set).
         RegsForValue RFV(V->getContext(), TLI, DAG.getDataLayout(), Reg,
                          V->getType(), None);
         if (RFV.occupiesMultipleRegs()) {
Index: llvm/trunk/test/DebugInfo/X86/sdag-dbgvalue-ssareg.ll
===================================================================
--- llvm/trunk/test/DebugInfo/X86/sdag-dbgvalue-ssareg.ll
+++ llvm/trunk/test/DebugInfo/X86/sdag-dbgvalue-ssareg.ll
@@ -0,0 +1,60 @@
+; RUN: llc -start-after=codegenprepare -stop-before expand-isel-pseudos -o - %s | FileCheck %s
+
+; Test that dbg.values of an SSA variable that's not used in a basic block,
+; is converted to a DBG_VALUE in that same basic block. We know that %1 is
+; live from the entry bb to the exit bb, is allocated a vreg because it's
+; used across basic blocks. We should be able to produce a DBG_VALUE that
+; refers to it in the nextbb block.
+
+source_filename = "debug.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define dso_local i32 @main(i32 %arg0, i32 %arg1) local_unnamed_addr !dbg !11 {
+entry:
+  %0 = add i32 %arg0, 42, !dbg !26
+  %1 = add i32 %arg1, 101, !dbg !26
+  %cmp = icmp eq i32 %1, 0
+  br i1 %cmp, label %nextbb, label %exit, !dbg !26
+
+nextbb:
+; CHECK-LABEL: bb.{{.*}}.nextbb
+  %2 = mul i32 %0, %arg1, !dbg !26
+; CHECK: IMUL32rr
+  call void @llvm.dbg.value(metadata i32 %1, metadata !16, metadata !DIExpression()), !dbg !27
+; CHECK-NEXT: DBG_VALUE
+  br label %exit, !dbg !26
+
+; CHECK-LABEL: bb.{{.*}}.exit
+exit:
+  %3 = phi i32 [ 12, %entry ], [ %2, %nextbb ], !dbg !26
+  %4 = add i32 %1, %3, !dbg !26
+  ret i32 %4, !dbg !26
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 7.0.0 (x)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4)
+!3 = !DIFile(filename: "debug.c", directory: "")
+!4 = !{}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{!"clang version 7.0.0 (x)"}
+!11 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 3, type: !12, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: true, unit: !2, retainedNodes: !14)
+!12 = !DISubroutineType(types: !13)
+!13 = !{!6}
+!14 = !{!16}
+!16 = !DILocalVariable(name: "y", scope: !11, file: !3, line: 5, type: !6)
+!26 = !DILocation(line: 4, column: 7, scope: !11)
+!27 = !DILocation(line: 5, column: 7, scope: !11)
+!31 = !{!32, !32, i64 0}
+!32 = !{!"int", !33, i64 0}
+!33 = !{!"omnipotent char", !34, i64 0}
+!34 = !{!"Simple C/C++ TBAA"}