diff --git a/llvm/lib/CodeGen/CalcSpillWeights.cpp b/llvm/lib/CodeGen/CalcSpillWeights.cpp
--- a/llvm/lib/CodeGen/CalcSpillWeights.cpp
+++ b/llvm/lib/CodeGen/CalcSpillWeights.cpp
@@ -203,9 +203,10 @@
   };
   std::set<CopyHint> CopyHints;
 
-  for (MachineRegisterInfo::reg_instr_iterator
-       I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end();
-       I != E; ) {
+  for (MachineRegisterInfo::reg_instr_nodbg_iterator
+           I = mri.reg_instr_nodbg_begin(li.reg),
+           E = mri.reg_instr_nodbg_end();
+       I != E;) {
     MachineInstr *mi = &*(I++);
 
     // For local split artifacts, we are interested only in instructions between
@@ -215,7 +216,7 @@
       continue;
 
     numInstr++;
-    if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugInstr())
+    if (mi->isIdentityCopy() || mi->isImplicitDef())
       continue;
     if (!visited.insert(mi).second)
       continue;
diff --git a/llvm/test/CodeGen/Generic/csw-debug-assert.ll b/llvm/test/CodeGen/Generic/csw-debug-assert.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/Generic/csw-debug-assert.ll
@@ -0,0 +1,113 @@
+; REQUIRES: asserts
+; RUN: llc -O1 -regalloc=pbqp %s -o %t.o
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind uwtable
+define dso_local void @test(i16* noalias %a, i16* noalias %b, i16* noalias %c, i32 %n) local_unnamed_addr #0 !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i16* %a, metadata !22, metadata !DIExpression()), !dbg !30
+  call void @llvm.dbg.value(metadata i16* %b, metadata !23, metadata !DIExpression()), !dbg !30
+  call void @llvm.dbg.value(metadata i16* %c, metadata !24, metadata !DIExpression()), !dbg !30
+  call void @llvm.dbg.value(metadata i32 %n, metadata !25, metadata !DIExpression()), !dbg !30
+  call void @llvm.dbg.value(metadata i32 0, metadata !26, metadata !DIExpression()), !dbg !31
+  br label %for.cond, !dbg !32
+
+for.cond:                                         ; preds = %for.body, %entry
+  %b.addr.0 = phi i16* [ %b, %entry ], [ %incdec.ptr1, %for.body ]
+  %c.addr.0 = phi i16* [ %c, %entry ], [ %incdec.ptr4, %for.body ]
+  %a.addr.0 = phi i16* [ %a, %entry ], [ %incdec.ptr, %for.body ]
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.body ], !dbg !31
+  call void @llvm.dbg.value(metadata i32 %i.0, metadata !26, metadata !DIExpression()), !dbg !31
+  call void @llvm.dbg.value(metadata i16* %a.addr.0, metadata !22, metadata !DIExpression()), !dbg !30
+  call void @llvm.dbg.value(metadata i16* %c.addr.0, metadata !24, metadata !DIExpression()), !dbg !30
+  call void @llvm.dbg.value(metadata i16* %b.addr.0, metadata !23, metadata !DIExpression()), !dbg !30
+  %cmp = icmp ult i32 %i.0, %n, !dbg !33
+  br i1 %cmp, label %for.body, label %for.cond.cleanup, !dbg !35
+
+for.cond.cleanup:                                 ; preds = %for.cond
+  ret void, !dbg !36
+
+for.body:                                         ; preds = %for.cond
+  %incdec.ptr = getelementptr inbounds i16, i16* %a.addr.0, i32 1, !dbg !37
+  call void @llvm.dbg.value(metadata i16* %incdec.ptr, metadata !22, metadata !DIExpression()), !dbg !30
+  %0 = load i16, i16* %a.addr.0, align 2, !dbg !39, !tbaa !40
+  %conv = sext i16 %0 to i32, !dbg !39
+  %incdec.ptr1 = getelementptr inbounds i16, i16* %b.addr.0, i32 1, !dbg !44
+  call void @llvm.dbg.value(metadata i16* %incdec.ptr1, metadata !23, metadata !DIExpression()), !dbg !30
+  %1 = load i16, i16* %b.addr.0, align 2, !dbg !45, !tbaa !40
+  %conv2 = sext i16 %1 to i32, !dbg !45
+  %add = add nsw i32 %conv, %conv2, !dbg !46
+  %conv3 = trunc i32 %add to i16, !dbg !39
+  %incdec.ptr4 = getelementptr inbounds i16, i16* %c.addr.0, i32 1, !dbg !47
+  call void @llvm.dbg.value(metadata i16* %incdec.ptr4, metadata !24, metadata !DIExpression()), !dbg !30
+  store i16 %conv3, i16* %c.addr.0, align 2, !dbg !48, !tbaa !40
+  %inc = add nsw i32 %i.0, 1, !dbg !49
+  call void @llvm.dbg.value(metadata i32 %inc, metadata !26, metadata !DIExpression()), !dbg !31
+  br label %for.cond, !dbg !50, !llvm.loop !51
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable optnone noinline "correctly-rounded-divide-sqrt-fp-math"="false" "denormal-fp-math"="ieee,ieee" "denormal-fp-math-f32"="ieee,ieee" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git afaeb817468d2fdc0a315a7ff136db245e59a8eb)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "csw-debug-assert.c", directory: "dir")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project.git afaeb817468d2fdc0a315a7ff136db245e59a8eb)"}
+!7 = distinct !DISubprogram(name: "test", scope: !8, file: !8, line: 6, type: !9, scopeLine: 6, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !21)
+!8 = !DIFile(filename: "csw-debug-assert.c", directory: "dir")
+!9 = !DISubroutineType(types: !10)
+!10 = !{null, !11, !11, !17, !19}
+!11 = !DIDerivedType(tag: DW_TAG_restrict_type, baseType: !12)
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+!13 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !14)
+!14 = !DIDerivedType(tag: DW_TAG_typedef, name: "int16_t", file: !15, line: 37, baseType: !16)
+!15 = !DIFile(filename: "/usr/include/stdint.h", directory: "")
+!16 = !DIBasicType(name: "short", size: 16, encoding: DW_ATE_signed)
+!17 = !DIDerivedType(tag: DW_TAG_restrict_type, baseType: !18)
+!18 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64)
+!19 = !DIDerivedType(tag: DW_TAG_typedef, name: "uint32_t", file: !15, line: 51, baseType: !20)
+!20 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!21 = !{!22, !23, !24, !25, !26}
+!22 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !8, line: 6, type: !11)
+!23 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !8, line: 6, type: !11)
+!24 = !DILocalVariable(name: "c", arg: 3, scope: !7, file: !8, line: 6, type: !17)
+!25 = !DILocalVariable(name: "n", arg: 4, scope: !7, file: !8, line: 6, type: !19)
+!26 = !DILocalVariable(name: "i", scope: !27, file: !8, line: 7, type: !28)
+!27 = distinct !DILexicalBlock(scope: !7, file: !8, line: 7, column: 5)
+!28 = !DIDerivedType(tag: DW_TAG_typedef, name: "int32_t", file: !15, line: 38, baseType: !29)
+!29 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!30 = !DILocation(line: 0, scope: !7)
+!31 = !DILocation(line: 0, scope: !27)
+!32 = !DILocation(line: 7, column: 10, scope: !27)
+!33 = !DILocation(line: 7, column: 27, scope: !34)
+!34 = distinct !DILexicalBlock(scope: !27, file: !8, line: 7, column: 5)
+!35 = !DILocation(line: 7, column: 5, scope: !27)
+!36 = !DILocation(line: 10, column: 1, scope: !7)
+!37 = !DILocation(line: 8, column: 18, scope: !38)
+!38 = distinct !DILexicalBlock(scope: !34, file: !8, line: 7, column: 37)
+!39 = !DILocation(line: 8, column: 16, scope: !38)
+!40 = !{!41, !41, i64 0}
+!41 = !{!"short", !42, i64 0}
+!42 = !{!"omnipotent char", !43, i64 0}
+!43 = !{!"Simple C/C++ TBAA"}
+!44 = !DILocation(line: 8, column: 25, scope: !38)
+!45 = !DILocation(line: 8, column: 23, scope: !38)
+!46 = !DILocation(line: 8, column: 21, scope: !38)
+!47 = !DILocation(line: 8, column: 11, scope: !38)
+!48 = !DILocation(line: 8, column: 14, scope: !38)
+!49 = !DILocation(line: 7, column: 33, scope: !34)
+!50 = !DILocation(line: 7, column: 5, scope: !34)
+!51 = distinct !{!51, !35, !52}
+!52 = !DILocation(line: 9, column: 5, scope: !27)