[CodeGen] Be as conservative about atomic accesses as for volatile

Background: At the moment, we record the AtomicOrdering of an access in the MMO, but also mark any atomic access as volatile in SelectionDAG. I'm working towards separating that. See https://reviews.llvm.org/D57601 for context.

Update all usages of isVolatile in lib/CodeGen to preserve behaviour once atomic MMOs stop being also volatile. This is NFC in it's current form, but is essential for correctness once we make that final change.

It useful to keep in mind that AtomicSDNode is not a parent of LoadSDNode, StoreSDNode, or LSBaseSDNode. As a result, any call to isVolatile on one of those static types doesn't need a companion isAtomic check.  We should probably adjust that class hierarchy long term, but for now, that seperation is useful.

I'm deliberately being conservative about handling. I want the change to stop adding volatile to be NFC itself, and then will work through places where we can be less conservative for atomics one by one in separate changes w/tests.

Differential Revision: https://reviews.llvm.org/D57596

llvm-svn: 352937

llvm/lib/CodeGen/MachineInstr.cpp

@@ -1305,6 +1305,8 @@ bool MachineInstr::isDereferenceableInvariantLoad(AliasAnalysis *AA) const {
 
   for (MachineMemOperand *MMO : memoperands()) {
     if (MMO->isVolatile()) return false;
+    // TODO: Figure out whether isAtomic is really necessary (see D57601).
+    if (MMO->isAtomic()) return false;
     if (MMO->isStore()) return false;
     if (MMO->isInvariant() && MMO->isDereferenceable())
       continue;

llvm/lib/CodeGen/MachinePipeliner.cpp

@@ -2766,7 +2766,9 @@ void SwingSchedulerDAG::updateMemOperands(MachineInstr &NewMI,
     return;
   SmallVector<MachineMemOperand *, 2> NewMMOs;
   for (MachineMemOperand *MMO : NewMI.memoperands()) {
-    if (MMO->isVolatile() || (MMO->isInvariant() && MMO->isDereferenceable()) ||
+    // TODO: Figure out whether isAtomic is really necessary (see D57601).
+    if (MMO->isVolatile() || MMO->isAtomic() ||
+        (MMO->isInvariant() && MMO->isDereferenceable()) ||
         (!MMO->getValue())) {
       NewMMOs.push_back(MMO);
       continue;

llvm/lib/CodeGen/ScheduleDAGInstrs.cpp

@@ -131,7 +131,8 @@ static bool getUnderlyingObjectsForInstr(const MachineInstr *MI,
                                          const DataLayout &DL) {
   auto allMMOsOkay = [&]() {
     for (const MachineMemOperand *MMO : MI->memoperands()) {
-      if (MMO->isVolatile())
+      // TODO: Figure out whether isAtomic is really necessary (see D57601).
+      if (MMO->isVolatile() || MMO->isAtomic())
         return false;
 
       if (const PseudoSourceValue *PSV = MMO->getPseudoValue()) {