diff --git a/llvm/lib/IR/LLVMContextImpl.h b/llvm/lib/IR/LLVMContextImpl.h
--- a/llvm/lib/IR/LLVMContextImpl.h
+++ b/llvm/lib/IR/LLVMContextImpl.h
@@ -513,11 +513,20 @@
 
   bool isKeyOf(const DIStringType *RHS) const {
     return Tag == RHS->getTag() && Name == RHS->getRawName() &&
+           StringLength == RHS->getRawStringLength() &&
+           StringLengthExp == RHS->getRawStringLengthExp() &&
+           StringLocationExp == RHS->getRawStringLocationExp() &&
            SizeInBits == RHS->getSizeInBits() &&
            AlignInBits == RHS->getAlignInBits() &&
            Encoding == RHS->getEncoding();
   }
-  unsigned getHashValue() const { return hash_combine(Tag, Name, Encoding); }
+  unsigned getHashValue() const {
+    // Intentionally computes the hash on a subset of the operands for
+    // performance reason. The subset has to be significant enough to avoid
+    // collision "most of the time". There is no correctness issue in case of
+    // collision because of the full check above.
+    return hash_combine(Tag, Name, StringLength, Encoding);
+  }
 };
 
 template <> struct MDNodeKeyImpl<DIDerivedType> {
diff --git a/llvm/test/DebugInfo/Inputs/distringtype1.ll b/llvm/test/DebugInfo/Inputs/distringtype1.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/Inputs/distringtype1.ll
@@ -0,0 +1,29 @@
+define void @sub2_(ptr %string, i64 %.U0001.arg) !dbg !5 {
+L.entry:
+  call void @llvm.dbg.declare(metadata ptr %string, metadata !12, metadata !DIExpression()), !dbg !14
+  call void @llvm.dbg.value(metadata i64 %.U0001.arg, metadata !10, metadata !DIExpression()), !dbg !14
+  ret void, !dbg !15
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!0, !1}
+!llvm.dbg.cu = !{!2}
+
+!0 = !{i32 2, !"Dwarf Version", i32 4}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !3, producer: " F90 Flang - 1.5 2017-05-01", isOptimized: false, flags: "'+flang -g distringtype1.f90 -S -emit-llvm'", runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !4, globals: !4, imports: !4, nameTableKind: None)
+!3 = !DIFile(filename: "distringtype1.f90", directory: "/tmp/")
+!4 = !{}
+!5 = distinct !DISubprogram(name: "sub2", scope: !2, file: !3, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !9)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null, !8}
+!8 = !DIStringType(name: "character(*)!1", size: 32)
+!9 = !{!10, !12}
+!10 = !DILocalVariable(arg: 2, scope: !5, file: !3, line: 1, type: !11, flags: DIFlagArtificial)
+!11 = !DIBasicType(name: "integer*8", size: 64, align: 64, encoding: DW_ATE_signed)
+!12 = !DILocalVariable(name: "string", arg: 1, scope: !5, file: !3, line: 1, type: !13)
+!13 = !DIStringType(name: "character(*)!2", stringLength: !10, stringLengthExpression: !DIExpression(), size: 32)
+!14 = !DILocation(line: 0, scope: !5)
+!15 = !DILocation(line: 3, column: 1, scope: !5)
diff --git a/llvm/test/DebugInfo/distringtype.ll b/llvm/test/DebugInfo/distringtype.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/distringtype.ll
@@ -0,0 +1,45 @@
+; RUN: llvm-link %s %p/Inputs/distringtype1.ll -S -o - | FileCheck %s
+
+; This test checks that DIStringType is properly linked.
+
+; CHECK: !DIStringType(name: "character(*)!1", size: 32)
+; CHECK: !DIStringType(name: "character(*)!2", size: 32)
+; CHECK: !DIStringType(name: "character(*)!3", stringLength: !{{[0-9]+}}, stringLengthExpression: !DIExpression(), size: 32)
+; CHECK: !DIStringType(name: "character(*)!4", stringLength: !{{[0-9]+}}, stringLengthExpression: !DIExpression(), size: 32)
+; CHECK: !DIStringType(name: "character(*)!2", stringLength: !{{[0-9]+}}, stringLengthExpression: !DIExpression(), size: 32)
+
+define void @sub1_(ptr %string1, ptr %string2, i64 %.U0002.arg, i64 %.U0003.arg) !dbg !5 {
+L.entry:
+  call void @llvm.dbg.declare(metadata ptr %string1, metadata !13, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.declare(metadata ptr %string2, metadata !16, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i64 %.U0002.arg, metadata !11, metadata !DIExpression()), !dbg !18
+  call void @llvm.dbg.value(metadata i64 %.U0003.arg, metadata !15, metadata !DIExpression()), !dbg !18
+  ret void, !dbg !19
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!0, !1}
+!llvm.dbg.cu = !{!2}
+
+!0 = !{i32 2, !"Dwarf Version", i32 4}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !3, producer: " F90 Flang - 1.5 2017-05-01", isOptimized: false, flags: "'+flang -g distringtype.f90 -S -emit-llvm'", runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !4, globals: !4, imports: !4, nameTableKind: None)
+!3 = !DIFile(filename: "distringtype.f90", directory: "/tmp/")
+!4 = !{}
+!5 = distinct !DISubprogram(name: "sub1", scope: !2, file: !3, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !10)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null, !8, !9}
+!8 = !DIStringType(name: "character(*)!1", size: 32)
+!9 = !DIStringType(name: "character(*)!2", size: 32)
+!10 = !{!11, !13, !15, !16}
+!11 = !DILocalVariable(arg: 3, scope: !5, file: !3, line: 1, type: !12, flags: DIFlagArtificial)
+!12 = !DIBasicType(name: "integer*8", size: 64, align: 64, encoding: DW_ATE_signed)
+!13 = !DILocalVariable(name: "string1", arg: 1, scope: !5, file: !3, line: 1, type: !14)
+!14 = !DIStringType(name: "character(*)!3", stringLength: !11, stringLengthExpression: !DIExpression(), size: 32)
+!15 = !DILocalVariable(arg: 4, scope: !5, file: !3, line: 1, type: !12, flags: DIFlagArtificial)
+!16 = !DILocalVariable(name: "string2", arg: 2, scope: !5, file: !3, line: 1, type: !17)
+!17 = !DIStringType(name: "character(*)!4", stringLength: !15, stringLengthExpression: !DIExpression(), size: 32)
+!18 = !DILocation(line: 0, scope: !5)
+!19 = !DILocation(line: 4, column: 1, scope: !5)