[dsymutil] Don't clone empty CUs

The DWARF standard says that an empty compile unit is not valid:

> Each such contribution consists of a compilation unit header (see
> Section 7.5.1.1 on page 200) followed by a single DW_TAG_compile_unit or
> DW_TAG_partial_unit debugging information entry, together with its
> children.

Therefore we shouldn't clone them in dsymutil.

Differential revision: https://reviews.llvm.org/D57979

llvm-svn: 353903

2 files changed, 8 insertions, 9 deletions

diff --git a/llvm/tools/dsymutil/CompileUnit.cpp b/llvm/tools/dsymutil/CompileUnit.cpp
index 3eb6abbb852..670591a9436 100644
--- a/llvm/tools/dsymutil/CompileUnit.cpp
+++ b/llvm/tools/dsymutil/CompileUnit.cpp
@@ -55,12 +55,11 @@ void CompileUnit::markEverythingAsKept() {
 }
 
 uint64_t CompileUnit::computeNextUnitOffset() {
-  NextUnitOffset = StartOffset + 11 /* Header size */;
-  // The root DIE might be null, meaning that the Unit had nothing to
-  // contribute to the linked output. In that case, we will emit the
-  // unit header without any actual DIE.
-  if (NewUnit)
+  NextUnitOffset = StartOffset;
+  if (NewUnit) {
+    NextUnitOffset += 11 /* Header size */;
     NextUnitOffset += NewUnit->getUnitDie().getSize();
+  }
   return NextUnitOffset;
 }
 
diff --git a/llvm/tools/dsymutil/DwarfLinker.cpp b/llvm/tools/dsymutil/DwarfLinker.cpp
index 384805808e5..ce8653173c3 100644
--- a/llvm/tools/dsymutil/DwarfLinker.cpp
+++ b/llvm/tools/dsymutil/DwarfLinker.cpp
@@ -2266,10 +2266,10 @@ void DwarfLinker::DIECloner::cloneAllCompileUnits(
     if (LLVM_LIKELY(!Linker.Options.Update))
       Linker.generateUnitRanges(*CurrentUnit);
     CurrentUnit->fixupForwardReferences();
-    Linker.Streamer->emitCompileUnitHeader(*CurrentUnit);
-    if (!CurrentUnit->getOutputUnitDIE())
-      continue;
-    Linker.Streamer->emitDIE(*CurrentUnit->getOutputUnitDIE());
+    if (CurrentUnit->getOutputUnitDIE()) {
+      Linker.Streamer->emitCompileUnitHeader(*CurrentUnit);
+      Linker.Streamer->emitDIE(*CurrentUnit->getOutputUnitDIE());
+    }
   }
 }