llvm-dwp: Support empty .dwo files

Though a bit odd, this is handy for a few reasons - for example, in a
build system that wants consistent input/output of build steps, but
where split-dwarf might be overriden/disabled by the user on a per-file
basis.

llvm-svn: 261987

3 files changed, 19 insertions, 9 deletions

diff --git a/llvm/test/tools/llvm-dwp/Inputs/empty.dwo b/llvm/test/tools/llvm-dwp/Inputs/empty.dwo
new file mode 100644
index 00000000000..c48a82cf4d7
--- /dev/null
+++ b/llvm/test/tools/llvm-dwp/Inputs/empty.dwo
diff --git a/llvm/test/tools/llvm-dwp/X86/empty.test b/llvm/test/tools/llvm-dwp/X86/empty.test
new file mode 100644
index 00000000000..78e4eb9b889
--- /dev/null
+++ b/llvm/test/tools/llvm-dwp/X86/empty.test
@@ -0,0 +1,8 @@
+RUN: llvm-dwp %p/../Inputs/empty.dwo -o %t
+RUN: llvm-dwarfdump %t | FileCheck %s
+
+CHECK-LABEL: .debug_cu_index
+CHECK-NOT: version
+CHECK-LABEL: .debug_tu_index
+CHECK-NOT: version
+CHECK: .debug_
diff --git a/llvm/tools/llvm-dwp/llvm-dwp.cpp b/llvm/tools/llvm-dwp/llvm-dwp.cpp
index ca40638d801..82b7d12fcb1 100644
--- a/llvm/tools/llvm-dwp/llvm-dwp.cpp
+++ b/llvm/tools/llvm-dwp/llvm-dwp.cpp
@@ -219,6 +219,9 @@ static void
 writeIndex(MCStreamer &Out, MCSection *Section,
            ArrayRef<unsigned> ContributionOffsets,
            const MapVector<uint64_t, UnitIndexEntry> &IndexEntries) {
+  if (IndexEntries.empty())
+    return;
+
   unsigned Columns = 0;
   for (auto &C : ContributionOffsets)
     if (C)
@@ -397,8 +400,9 @@ static std::error_code write(MCStreamer &Out, ArrayRef<std::string> Inputs) {
       }
     }
 
-    assert(!AbbrevSection.empty());
-    assert(!InfoSection.empty());
+    if (InfoSection.empty())
+      continue;
+
     if (!CurCUIndexSection.empty()) {
       DWARFUnitIndex CUIndex(DW_SECT_INFO);
       DataExtractor CUIndexData(CurCUIndexSection,
@@ -448,13 +452,11 @@ static std::error_code write(MCStreamer &Out, ArrayRef<std::string> Inputs) {
       return Err;
   }
 
-  if (!TypeIndexEntries.empty()) {
-    // Lie about there being no info contributions so the TU index only includes
-    // the type unit contribution
-    ContributionOffsets[0] = 0;
-    writeIndex(Out, MCOFI.getDwarfTUIndexSection(), ContributionOffsets,
-               TypeIndexEntries);
-  }
+  // Lie about there being no info contributions so the TU index only includes
+  // the type unit contribution
+  ContributionOffsets[0] = 0;
+  writeIndex(Out, MCOFI.getDwarfTUIndexSection(), ContributionOffsets,
+             TypeIndexEntries);
 
   // Lie about the type contribution
   ContributionOffsets[DW_SECT_TYPES - DW_SECT_INFO] = 0;