Fix undefined behavior in DWARF emission

Caused by uninitialized load of llvm::DwarfDebug::PrevCU:
llvm::DwarfCompileUnit::addRange () at ../lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp:276
llvm::DwarfDebug::endFunctionImpl () at ../lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1586
llvm::DebugHandlerBase::endFunction () at ../lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp:319
llvm::AsmPrinter::EmitFunctionBody () at ../lib/CodeGen/AsmPrinter/AsmPrinter.cpp:1230
llvm::ARMAsmPrinter::runOnMachineFunction () at ../lib/Target/ARM/ARMAsmPrinter.cpp:161

Most of the DebugInfo tests under `LLVM_LIT_ARGS:STRING=-sv --vg` prior to this fix, and pass with the fix applied.

Reviewed By: aprantl, dblaikie

Differential Revision: https://reviews.llvm.org/D81631

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index d7a4b2a..ad2f2f3 100644 (file)
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -325,7 +325,7 @@ class DwarfDebug : public DebugHandlerBase {
   const MachineFunction *CurFn = nullptr;
 
   /// If nonnull, stores the CU in which the previous subprogram was contained.
-  const DwarfCompileUnit *PrevCU;
+  const DwarfCompileUnit *PrevCU = nullptr;
 
   /// As an optimization, there is no need to emit an entry in the directory
   /// table for the same directory as DW_AT_comp_dir.