CodeGen: Turn on sentinel tracking for MachineInstr iterators

This is a prep commit before fixing MachineBasicBlock::reverse_iterator
invalidation semantics, ala r281167 for ilist::reverse_iterator.  This
changes MachineBasicBlock::Instructions to track which node is the
sentinel regardless of LLVM_ENABLE_ABI_BREAKING_CHECKS.

There's almost no functionality change (aside from ABI).  However, in
the rare configuration:

    #if !defined(NDEBUG) && !defined(LLVM_ENABLE_ABI_BREAKING_CHECKS)

the isKnownSentinel() assertions in ilist_iterator<>::operator* suddenly
have teeth for MachineInstr.  If these assertions start firing for your
out-of-tree backend, have a look at the suggestions in the commit
message for r279314, and at some of the commits leading up to it that
avoid dereferencing the end() iterator.

llvm-svn: 281168

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/unittests/CodeGen/MachineInstrBundleIteratorTest.cpp b/llvm/unittests/CodeGen/MachineInstrBundleIteratorTest.cpp
index 857994a3b29..738d07d06a6 100644
--- a/llvm/unittests/CodeGen/MachineInstrBundleIteratorTest.cpp
+++ b/llvm/unittests/CodeGen/MachineInstrBundleIteratorTest.cpp
@@ -15,7 +15,8 @@ using namespace llvm;
 
 namespace {
 
-struct MyBundledInstr : public ilist_node<MyBundledInstr> {
+struct MyBundledInstr
+    : public ilist_node<MyBundledInstr, ilist_sentinel_tracking<true>> {
   bool isBundledWithPred() const { return true; }
   bool isBundledWithSucc() const { return true; }
 };