Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3052,7 +3052,10 @@
         }
       }
 
-      InstrsForInstCombineWorklist.push_back(Inst);
+      // Skip processing debug intrinsics in InstCombine. Processing these call instructions
+      // consumes non-trivial amount of time and provides no value for the optimization.
+      if (!isa<DbgInfoIntrinsic>(Inst))
+        InstrsForInstCombineWorklist.push_back(Inst);
     }
 
     // Recursively visit successors.  If this is a branch or switch on a
Index: test/Transforms/InstCombine/debuginfo-skip.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/debuginfo-skip.ll
@@ -0,0 +1,85 @@
+; RUN: opt < %s -instcombine -debug -S -o %t 2>&1 | FileCheck %s
+; RUN: cat %t | FileCheck %s --check-prefix=CHECK-IR
+
+; Debug output from InstCombine should not have any @llvm.dbg.* instructions visited
+; CHECK-NOT: call void @llvm.dbg.
+
+; The resulting IR should still have them
+; CHECK-IR: call void @llvm.dbg.
+
+%struct.moo = type { i32, i32, i32 }
+
+@foo.mymoo = private unnamed_addr constant %struct.moo { i32 1, i32 2, i32 3 }, align 4
+
+define i32 @bar(%struct.moo* %moo_p, i32 %i) #0 {
+entry:
+  call void @llvm.dbg.value(metadata %struct.moo* %moo_p, i64 0, metadata !18, metadata !20), !dbg !21
+  call void @llvm.dbg.value(metadata i32 %i, i64 0, metadata !19, metadata !20), !dbg !22
+  %i1 = getelementptr inbounds %struct.moo, %struct.moo* %moo_p, i32 0, i32 2
+  store i32 10, i32* %i1, align 4
+  %i2 = getelementptr inbounds %struct.moo, %struct.moo* %moo_p, i32 0, i32 2
+  %0 = load i32, i32* %i2, align 4
+  ret i32 %0
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+define i32 @foo() #0 !dbg !32 {
+entry:
+  %blah = alloca i32, align 4
+  %mymoo = alloca %struct.moo, align 4
+  %0 = bitcast i32* %blah to i8*
+  call void @llvm.dbg.declare(metadata i32* %blah, metadata !36, metadata !20), !dbg !39
+  store i32 10, i32* %blah, align 4
+  %1 = bitcast %struct.moo* %mymoo to i8*
+  call void @llvm.dbg.declare(metadata %struct.moo* %mymoo, metadata !37, metadata !20), !dbg !42
+  %2 = bitcast %struct.moo* %mymoo to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %2, i8* bitcast (%struct.moo* @foo.mymoo to i8*), i64 12, i32 4, i1 false)
+  %3 = load i32, i32* %blah, align 4
+  %call = call i32 @bar(%struct.moo* %mymoo, i32 %3), !dbg !44
+  %4 = bitcast %struct.moo* %mymoo to i8*
+  %5 = bitcast i32* %blah to i8*
+  ret i32 %call
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i32, i1) #2
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang 5.0.0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "a.c", directory: "/tmp")
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"PIC Level", i32 2}
+!7 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 5, type: !8, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !17)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !11, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "moo", file: !1, line: 1, size: 96, elements: !13)
+!13 = !{!14, !15, !16}
+!14 = !DIDerivedType(tag: DW_TAG_member, name: "j", scope: !12, file: !1, line: 2, baseType: !10, size: 32)
+!15 = !DIDerivedType(tag: DW_TAG_member, name: "k", scope: !12, file: !1, line: 2, baseType: !10, size: 32, offset: 32)
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "i", scope: !12, file: !1, line: 2, baseType: !10, size: 32, offset: 64)
+!17 = !{!18, !19}
+!18 = !DILocalVariable(name: "moo_p", arg: 1, scope: !7, file: !1, line: 5, type: !11)
+!19 = !DILocalVariable(name: "i", arg: 2, scope: !7, file: !1, line: 5, type: !10)
+!20 = !DIExpression()
+!21 = !DILocation(line: 5, column: 21, scope: !7)
+!22 = !DILocation(line: 5, column: 32, scope: !7)
+!25 = !{!26, !27, i64 8}
+!26 = !{!"moo", !27, i64 0, !27, i64 4, !27, i64 8}
+!27 = !{!"int", !28, i64 0}
+!28 = !{!"omnipotent char", !29, i64 0}
+!29 = !{!"Simple C/C++ TBAA"}
+!32 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 10, type: !33, isLocal: false, isDefinition: true, scopeLine: 10, isOptimized: true, unit: !0, variables: !35)
+!33 = !DISubroutineType(types: !34)
+!34 = !{!10}
+!35 = !{!36, !37}
+!36 = !DILocalVariable(name: "blah", scope: !32, file: !1, line: 11, type: !10)
+!37 = !DILocalVariable(name: "mymoo", scope: !32, file: !1, line: 12, type: !12)
+!39 = !DILocation(line: 11, column: 7, scope: !32)
+!42 = !DILocation(line: 12, column: 14, scope: !32)
+!44 = !DILocation(line: 13, column: 10, scope: !32)