[llvm] CodeGen: add a missing check for bit-slice overlap in CV (PR #75504)

Thu Dec 14 09:52:34 PST 2023

https://github.com/compnerd created https://github.com/llvm/llvm-project/pull/75504

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.

>From 66eb13df348077cb02734720c421696daa3a3939 Mon Sep 17 00:00:00 2001
From: Saleem Abdulrasool <abdulras at thebrowser.company>
Date: Thu, 14 Dec 2023 09:18:06 -0800
Subject: [PATCH] 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 |  6 ++
 .../DebugInfo/codeview-bit-slice-fragments.ll | 67 +++++++++++++++++++
 2 files changed, 73 insertions(+)
 create mode 100644 llvm/test/DebugInfo/codeview-bit-slice-fragments.ll

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 3a9d5fa3b936e0..dddc08b3bc0166 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -1397,6 +1397,12 @@ 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();
diff --git a/llvm/test/DebugInfo/codeview-bit-slice-fragments.ll b/llvm/test/DebugInfo/codeview-bit-slice-fragments.ll
new file mode 100644
index 00000000000000..693ac6e917f480
--- /dev/null
+++ b/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)

