CodeGen: add a missing check for bit-slice overlap in CV

Type dereferenced fragments are specified by offset and length in bits.
The representation in CodeView is defined in terms of byte offsets.  If
the bit slice overlaps at a byte that is included, we would create
invalid definition ranges.

Consider the following scenario:

~~~
01234567   01234567
---------+---------
 ====  ======
~~~

Here bits 1-4 are marked as defined as well as bits 7-9.  The byte range
for the second portion overlaps and so we would say that bytes 1 and 2
are valid though there is potentially a hole.  There is no way to
represent this in the defined range for the local variable in CodeView.
We simply can drop the fragment definition in such a scenario with the
variables are "optimized out".

Thanks to @rnk and @hjyamauchi for the discussion around this.

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -1368,6 +1368,12 @@ void CodeViewDebug::calculateRanges(
     if (Location->Register == 0 || Location->LoadChain.size() > 1)
       continue;
 
+    // Codeview can only express byte-aligned offsets, ensure that we have a
+    // byte-boundaried location.
+    if (Location->FragmentInfo)
+      if (Location->FragmentInfo->OffsetInBits % 8)
+        continue;
+
     LocalVarDef DR;
     DR.CVRegister = TRI->getCodeViewRegNum(Location->Register);
     DR.InMemory = !Location->LoadChain.empty();

llvm/test/DebugInfo/codeview-bit-slice-fragments.ll

@@ -0,0 +1,67 @@
+; RUN: llc -filetype asm -o - %s | FileCheck %s
+
+; Ensure that we do not emit any live ranges for the fragment as it is
+; bit-sliced which cannot be represented in CodeView.
+; CHECK-NOT: .cv_def_range
+
+source_filename = "/tmp/reduced.ll"
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-windows-msvc19.37.32825"
+
+define swifttailcc void @"$s12SourceKitLSP0aB6ServerC14workspaceTestsySay08LanguageD8Protocol19WorkspaceSymbolItemOGSgAE0iF7RequestVYaKFTY0_"() !dbg !5 {
+entryresume.0:
+  br label %.from.63
+
+.from.63:                                         ; preds = %.from.63, %entryresume.0
+  %lsr.iv = phi ptr [ %scevgep, %.from.63 ], [ null, %entryresume.0 ]
+  %0 = load i64, ptr %lsr.iv, align 8
+  %1 = load i64, ptr %lsr.iv, align 8
+  call void @llvm.dbg.value(metadata ptr %lsr.iv, metadata !9, metadata !DIExpression(DW_OP_deref, DW_OP_LLVM_fragment, 1, 1)), !dbg !22
+  call void @llvm.dbg.value(metadata ptr %lsr.iv, metadata !9, metadata !DIExpression(DW_OP_deref, DW_OP_LLVM_fragment, 2, 64)), !dbg !22
+  %2 = load volatile ptr, ptr null, align 8, !dbg !30
+  %scevgep = getelementptr i8, ptr %lsr.iv, i64 8
+  br label %.from.63
+}
+
+declare void @llvm.dbg.value(metadata %0, metadata %1, metadata %2) #0
+
+attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !1, producer: "Swift version 5.11-dev (LLVM 572a5a4fbafb69e, Swift ebbb9de104d5682)", isOptimized: true, flags: "-private-discriminator _A0745CB010D215CC0C4A68539F8BE5E9", runtimeVersion: 5, emissionKind: FullDebug, imports: !2, sysroot: "S:/Program Files/Swift/Platforms/Windows.platform/Developer/SDKs/Windows.sdk", sdk: "Windows.sdk")
+!1 = !DIFile(filename: "S:\\SourceCache\\swift-project\\sourcekit-lsp\\Sources\\SourceKitLSP\\TestDiscovery.swift", directory: "S:\\b\14")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DISubprogram(name: "workspaceTests", linkageName: "$s12SourceKitLSP0aB6ServerC14workspaceTestsySay08LanguageD8Protocol19WorkspaceSymbolItemOGSgAE0iF7RequestVYaKFTY0_", scope: !6, file: !1, line: 35, type: !7, scopeLine: 35, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, declaration: !8, retainedNodes: !2, thrownTypes: !2)
+!6 = !DIModule(scope: null, name: "SourceKitLSP", includePath: "S:\\SourceCache\\swift-project\\sourcekit-lsp\\Sources\\SourceKitLSP")
+!7 = !DISubroutineType(types: !2)
+!8 = !DISubprogram(name: "workspaceTests", linkageName: "$s12SourceKitLSP0aB6ServerC14workspaceTestsySay08LanguageD8Protocol19WorkspaceSymbolItemOGSgAE0iF7RequestVYaKFTY0_", scope: !6, file: !1, line: 35, type: !7, scopeLine: 35, spFlags: DISPFlagOptimized, thrownTypes: !2)
+!9 = !DILocalVariable(name: "$0", arg: 1, scope: !10, file: !1, line: 41, type: !18)
+!10 = distinct !DISubprogram(linkageName: "$s12SourceKitLSP0aB6ServerC14workspaceTestsySay08LanguageD8Protocol19WorkspaceSymbolItemOGSgAE0iF7RequestVYaKFSb12IndexStoreDB0J10OccurrenceVXEfU0_", scope: !11, file: !1, line: 41, type: !17, scopeLine: 41, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2, thrownTypes: !13)
+!11 = distinct !DISubprogram(name: "workspaceTests", linkageName: "$s12SourceKitLSP0aB6ServerC14workspaceTestsySay08LanguageD8Protocol19WorkspaceSymbolItemOGSgAE0iF7RequestVYaKF", scope: !6, file: !1, line: 35, type: !7, scopeLine: 35, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, declaration: !12, retainedNodes: !2, thrownTypes: !13)
+!12 = !DISubprogram(name: "workspaceTests", linkageName: "$s12SourceKitLSP0aB6ServerC14workspaceTestsySay08LanguageD8Protocol19WorkspaceSymbolItemOGSgAE0iF7RequestVYaKF", scope: !6, file: !1, line: 35, type: !7, scopeLine: 35, spFlags: DISPFlagOptimized, thrownTypes: !13)
+!13 = !{!14}
+!14 = !DICompositeType(tag: DW_TAG_structure_type, name: "Error", scope: !16, file: !15, size: 64, elements: !2, runtimeLang: DW_LANG_Swift, identifier: "$ss5Error_pD")
+!15 = !DIFile(filename: "S:\\Program Files\\Swift\\Platforms\\Windows.platform\DEveloper\\SDKs\\Windows.sdk\\usr\\lib\\swift\\windows\\Swift.swiftmodule\\x86_64-unknown-windows-msvc.swiftmodule", directory: "S:\\")
+!16 = !DIModule(scope: null, name: "Swift", configMacros: "\22-D_CRT_SECURE_NO_WARNINGS\22 \22-D_MT\22 \22-D_DLL\22", includePath: "S:/Program Files/Swift/Platforms/Windows.platform/Developer/SDKs/Windows.sdk\\usr\\lib\\swift\\windows\\Swift.swiftmodule\\x86_64-unknown-windows-msvc.swiftmodule")
+!17 = distinct !DISubroutineType(types: !2)
+!18 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !19)
+!19 = !DICompositeType(tag: DW_TAG_structure_type, name: "SymbolOccurrence", scope: !21, file: !20, size: 960, elements: !2, runtimeLang: DW_LANG_Swift, identifier: "$s12IndexStoreDB16SymbolOccurrenceVD")
+!20 = !DIFile(filename: "13\\swift\\IndexStoreDB.swiftmodule", directory: "S:\\b")
+!21 = !DIModule(scope: null, name: "IndexStoreDB", configMacros: "\22-D_CRT_SECURE_NO_WARNINGS\22 \22-D_MT\22 \22-D_DLL\22", includePath: "S:\\b\\13\\swift\\IndexStoreDB.swiftmodule")
+!22 = !DILocation(line: 41, scope: !10, inlinedAt: !23)
+!23 = distinct !DILocation(line: 0, scope: !24, inlinedAt: !28)
+!24 = distinct !DISubprogram(name: "filter", linkageName: "$ss14_ArrayProtocolPsE6filterySay7ElementQzGSbAEKXEKFSay12IndexStoreDB16SymbolOccurrenceVG_Tg5", scope: !16, file: !25, type: !26, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, declaration: !27, thrownTypes: !2)
+!25 = !DIFile(filename: "<compiler-generated>", directory: "")
+!26 = distinct !DISubroutineType(types: !2)
+!27 = !DISubprogram(name: "filter", linkageName: "$ss14_ArrayProtocolPsE6filterySay7ElementQzGSbAEKXEKFSay12IndexStoreDB16SymbolOccurrenceVG_Tg5", scope: !16, file: !25, type: !26, spFlags: DISPFlagLocalToUnit | DISPFlagOptimized, thrownTypes: !2)
+!28 = distinct !DILocation(line: 41, scope: !29)
+!29 = distinct !DILexicalBlock(scope: !5, file: !1, line: 36)
+!30 = !DILocation(line: 24, scope: !31, inlinedAt: !34)
+!31 = distinct !DILexicalBlock(scope: !32, file: !1, line: 24)
+!32 = distinct !DISubprogram(name: "canBeTestDefinition.get", linkageName: "$s12IndexStoreDB16SymbolOccurrenceV12SourceKitLSPE19canBeTestDefinition33_A0745CB010D215CC0C4A68539F8BE5E9LLSbvg", scope: !6, file: !1, line: 23, type: !17, scopeLine: 23, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, declaration: !33, retainedNodes: !2)
+!33 = !DISubprogram(name: "canBeTestDefinition.get", linkageName: "$s12IndexStoreDB16SymbolOccurrenceV12SourceKitLSPE19canBeTestDefinition33_A0745CB010D215CC0C4A68539F8BE5E9LLSbvg", scope: !6, file: !1, line: 23, type: !17, scopeLine: 23, spFlags: DISPFlagLocalToUnit | DISPFlagOptimized)
+!34 = distinct !DILocation(line: 41, scope: !10, inlinedAt: !23)