DebugInfo: Include .dwo file name when hashing multiple CUs in a single file

This is really a workaround for ThinLTO in particular - since it can
import partial CUs that may end up looking very similar/the same as
the same partial import in another ThinLTO compile.

An alternative fix would be to change the DICompileUnit metadata to
include a "primary file" or the like - and when importing for ThinLTO
set the primary file to the name of the DICompileUnit that is being
imported into. This involves changing the schema and would reduce the
excessive uniqueness in the hash that this change creates - allowing
diagnosing of more duplicate CUs than will be caught with this change.

But duplicate CUs can still be caught in non-ThinLTO builds & are mostly
a nuisance rather than a particularly deliberate/effective tool for
finding broken code. (arguably the hash could always include the dwo
file and nothing in fission would break, I think..)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304119 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/AsmPrinter/DIEHash.cpp b/lib/CodeGen/AsmPrinter/DIEHash.cpp
index ff04ec7f2d780824667b3a5c1a2767e1cd8816c7..201030f0ac5cc7fe9e20475aaacffabbe17b7f54 100644 (file)
--- a/lib/CodeGen/AsmPrinter/DIEHash.cpp
+++ b/lib/CodeGen/AsmPrinter/DIEHash.cpp
@@ -380,10 +380,12 @@ void DIEHash::computeHash(const DIE &Die) {
 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
 /// with the inclusion of the full CU and all top level CU entities.
 // TODO: Initialize the type chain at 0 instead of 1 for CU signatures.
-uint64_t DIEHash::computeCUSignature(const DIE &Die) {
+uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) {
   Numbering.clear();
   Numbering[&Die] = 1;
 
+  if (!DWOName.empty())
+    Hash.update(DWOName);
   // Hash the DIE.
   computeHash(Die);
 

diff --git a/lib/CodeGen/AsmPrinter/DIEHash.h b/lib/CodeGen/AsmPrinter/DIEHash.h
index e2864b17fe2b43f53b028b310f40d57ac0009c5d..29337ae38a996b699fd50c3b2236690b87fbbc8a 100644 (file)
--- a/lib/CodeGen/AsmPrinter/DIEHash.h
+++ b/lib/CodeGen/AsmPrinter/DIEHash.h
@@ -36,7 +36,7 @@ public:
   DIEHash(AsmPrinter *A = nullptr) : AP(A) {}
 
   /// \brief Computes the CU signature.
-  uint64_t computeCUSignature(const DIE &Die);
+  uint64_t computeCUSignature(StringRef DWOName, const DIE &Die);
 
   /// \brief Computes the type signature.
   uint64_t computeTypeSignature(const DIE &Die);

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 06358c42cfe956beddefe147437dc17099151bb9..bf27516e1ccd0d3bf349603a11a5be3b347c83bb 100644 (file)
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -613,6 +613,13 @@ void DwarfDebug::finalizeModuleInfo() {
 
   finishVariableDefinitions();
 
+  // Include the DWO file name in the hash if there's more than one CU.
+  // This handles ThinLTO's situation where imported CUs may very easily be
+  // duplicate with the same CU partially imported into another ThinLTO unit.
+  StringRef DWOName;
+  if (CUMap.size() > 1)
+    DWOName = Asm->TM.Options.MCOptions.SplitDwarfFile;
+
   // Handle anything that needs to be done on a per-unit basis after
   // all other generation.
   for (const auto &P : CUMap) {
@@ -627,7 +634,8 @@ void DwarfDebug::finalizeModuleInfo() {
     auto *SkCU = TheCU.getSkeleton();
     if (useSplitDwarf()) {
       // Emit a unique identifier for this CU.
-      uint64_t ID = DIEHash(Asm).computeCUSignature(TheCU.getUnitDie());
+      uint64_t ID =
+          DIEHash(Asm).computeCUSignature(DWOName, TheCU.getUnitDie());
       TheCU.addUInt(TheCU.getUnitDie(), dwarf::DW_AT_GNU_dwo_id,
                     dwarf::DW_FORM_data8, ID);
       SkCU->addUInt(SkCU->getUnitDie(), dwarf::DW_AT_GNU_dwo_id,

diff --git a/test/DebugInfo/Generic/split-dwarf-multiple-cu-hash.ll b/test/DebugInfo/Generic/split-dwarf-multiple-cu-hash.ll
new file mode 100644 (file)
index 0000000..a6a83d8
--- /dev/null
+++ b/test/DebugInfo/Generic/split-dwarf-multiple-cu-hash.ll
@@ -0,0 +1,40 @@
+; RUN: %llc_dwarf -split-dwarf-file=foo.dwo  %s -filetype=obj -o %T/a.o
+; RUN: %llc_dwarf -split-dwarf-file=bar.dwo  %s -filetype=obj -o %T/b.o
+; RUN: llvm-dwarfdump -debug-dump=info %T/a.o %T/b.o | FileCheck %s
+
+; CHECK: dwo_id {{.*}}([[HASH:.*]])
+; CHECK-NOT: dwo_id {{.*}}([[HASH]])
+
+; Function Attrs: noinline nounwind uwtable
+define void @_Z1av() #0 !dbg !9 {
+entry:
+  ret void, !dbg !12
+}
+
+; Function Attrs: noinline nounwind uwtable
+define void @_Z1bv() #0 !dbg !13 {
+entry:
+  ret void, !dbg !14
+}
+
+attributes #0 = { noinline nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0, !3}
+!llvm.ident = !{!5, !5}
+!llvm.module.flags = !{!6, !7, !8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 304107) (llvm/trunk 304109)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "a.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch")
+!2 = !{}
+!3 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4, producer: "clang version 5.0.0 (trunk 304107) (llvm/trunk 304109)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!4 = !DIFile(filename: "b.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch")
+!5 = !{!"clang version 5.0.0 (trunk 304107) (llvm/trunk 304109)"}
+!6 = !{i32 2, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 4}
+!9 = distinct !DISubprogram(name: "a", linkageName: "_Z1av", scope: !1, file: !1, line: 1, type: !10, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!10 = !DISubroutineType(types: !11)
+!11 = !{null}
+!12 = !DILocation(line: 2, column: 1, scope: !9)
+!13 = distinct !DISubprogram(name: "b", linkageName: "_Z1bv", scope: !4, file: !4, line: 1, type: !10, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !3, variables: !2)
+!14 = !DILocation(line: 2, column: 1, scope: !13)