[AArch64] Keep track of MIFlags in the LoadStoreOptimizer

Merging:

* $x26, $x25 = frame-setup LDPXi $sp, 0
* $sp = frame-destroy ADDXri $sp, 64, 0

into an LDPXpost should preserve the flags from both instructions as
following:

* frame-setup frame-destroy LDPXpost

Differential Revision: https://reviews.llvm.org/D44446

llvm-svn: 327533

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 5f3989b..3fbf50d 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -381,6 +381,12 @@ MachineInstr::mergeMemRefsWith(const MachineInstr& Other) {
   return std::make_pair(MemBegin, CombinedNumMemRefs);
 }
 
+uint8_t MachineInstr::mergeFlagsWith(const MachineInstr &Other) const {
+  // For now, the just return the union of the flags. If the flags get more
+  // complicated over time, we might need more logic here.
+  return getFlags() | Other.getFlags();
+}
+
 bool MachineInstr::hasPropertyInBundle(unsigned Mask, QueryType Type) const {
   assert(!isBundledWithPred() && "Must be called on bundle header");
   for (MachineBasicBlock::const_instr_iterator MII = getIterator();; ++MII) {