Zero-Initialize PrevInstBB when entering a new MachineFunction.

It is not guaranteed that the memory used for MachineBasicBlocks in
the previous MachineFunction hasn't been freed, so holding on to a
pointer to the last function's isn't correct. Particularly I have
observed the sret.ll testcase failing because the first BasicBlock in
the new function happened to be allocated to the exact same memory as
the previously saved and (deleted) PrevInstBB.

llvm-svn: 298642

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
index aa8b8fb..1d63e33 100644 (file)
--- a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
@@ -130,6 +130,7 @@ bool hasDebugInfo(const MachineModuleInfo *MMI, const MachineFunction *MF) {
 
 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
   assert(Asm);
+  PrevInstBB = nullptr;
 
   if (!hasDebugInfo(MMI, MF)) {
     skippedNonDebugFunction();