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 +1,80 @@
+; Check that compiler doesn't crash when calculateSpillWeightsAndHints is called with dbg instrs present
+; REQUIRES: asserts
+; RUN: llc -O1 -regalloc=pbqp < %s | FileCheck %s
+
+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"
+
+; CHECK-LABEL: test:
+define dso_local void @test(i32* %a) local_unnamed_addr #0 !dbg !7 {
+entry:
+  ; CHECK: DEBUG_VALUE: i <- 0
+  call void @llvm.dbg.value(metadata i32* %a, metadata !14, metadata !DIExpression()), !dbg !17
+  call void @llvm.dbg.value(metadata i32 0, metadata !15, metadata !DIExpression()), !dbg !18
+  br label %for.cond, !dbg !19
+
+for.cond:                                         ; preds = %for.body, %entry
+  %a.addr.0 = phi i32* [ %a, %entry ], [ %incdec.ptr, %for.body ]
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.body ], !dbg !18
+  call void @llvm.dbg.value(metadata i32 %i.0, metadata !15, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i32* %a.addr.0, metadata !14, metadata !DIExpression()), !dbg !17
+  %cmp = icmp slt i32 %i.0, 32, !dbg !20
+  br i1 %cmp, label %for.body, label %for.cond.cleanup, !dbg !22
+
+for.cond.cleanup:                                 ; preds = %for.cond
+  ret void, !dbg !23
+
+for.body:                                         ; preds = %for.cond
+  %incdec.ptr = getelementptr inbounds i32, i32* %a.addr.0, i32 1, !dbg !24
+  call void @llvm.dbg.value(metadata i32* %incdec.ptr, metadata !14, metadata !DIExpression()), !dbg !17
+  store i32 42, i32* %a.addr.0, align 4, !dbg !26, !tbaa !27
+  %inc = add nsw i32 %i.0, 1, !dbg !31
+  call void @llvm.dbg.value(metadata i32 %inc, metadata !15, metadata !DIExpression()), !dbg !18
+  br label %for.cond, !dbg !32, !llvm.loop !33
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable optnone noinline }
+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: 5, type: !9, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !13)
+!8 = !DIFile(filename: "csw-debug-assert.c", directory: "dir")
+!9 = !DISubroutineType(types: !10)
+!10 = !{null, !11}
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !{!14, !15}
+!14 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !8, line: 5, type: !11)
+!15 = !DILocalVariable(name: "i", scope: !16, file: !8, line: 6, type: !12)
+!16 = distinct !DILexicalBlock(scope: !7, file: !8, line: 6, column: 5)
+!17 = !DILocation(line: 0, scope: !7)
+!18 = !DILocation(line: 0, scope: !16)
+!19 = !DILocation(line: 6, column: 10, scope: !16)
+!20 = !DILocation(line: 6, column: 23, scope: !21)
+!21 = distinct !DILexicalBlock(scope: !16, file: !8, line: 6, column: 5)
+!22 = !DILocation(line: 6, column: 5, scope: !16)
+!23 = !DILocation(line: 9, column: 1, scope: !7)
+!24 = !DILocation(line: 7, column: 11, scope: !25)
+!25 = distinct !DILexicalBlock(scope: !21, file: !8, line: 6, column: 34)
+!26 = !DILocation(line: 7, column: 14, scope: !25)
+!27 = !{!28, !28, i64 0}
+!28 = !{!"int", !29, i64 0}
+!29 = !{!"omnipotent char", !30, i64 0}
+!30 = !{!"Simple C/C++ TBAA"}
+!31 = !DILocation(line: 6, column: 30, scope: !21)
+!32 = !DILocation(line: 6, column: 5, scope: !21)
+!33 = distinct !{!33, !22, !34}
+!34 = !DILocation(line: 8, column: 5, scope: !16)