[CodeGen] Split out the notions of MI invariance and MI dereferenceability.

Summary:
An IR load can be invariant, dereferenceable, neither, or both.  But
currently, MI's notion of invariance is IR-invariant &&
IR-dereferenceable.

This patch splits up the notions of invariance and dereferenceability at
the MI level.  It's NFC, so adds some probably-unnecessary
"is-dereferenceable" checks, which we can remove later if desired.

Reviewers: chandlerc, tstellarAMD

Subscribers: jholewinski, arsenm, nemanjai, llvm-commits

Differential Revision: https://reviews.llvm.org/D23371

llvm-svn: 281151

1 files changed, 6 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 5e9bc0da871..e67915b2909 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2010,7 +2010,8 @@ static SDValue getLoadStackGuard(SelectionDAG &DAG, const SDLoc &DL,
   if (Global) {
     MachinePointerInfo MPInfo(Global);
     MachineInstr::mmo_iterator MemRefs = MF.allocateMemRefsArray(1);
-    auto Flags = MachineMemOperand::MOLoad | MachineMemOperand::MOInvariant;
+    auto Flags = MachineMemOperand::MOLoad | MachineMemOperand::MOInvariant |
+                 MachineMemOperand::MODereferenceable;
     *MemRefs = MF.getMachineMemOperand(MPInfo, Flags, PtrTy.getSizeInBits() / 8,
                                        DAG.getEVTAlignment(PtrTy));
     Node->setMemRefs(MemRefs, MemRefs + 1);
@@ -3473,17 +3474,8 @@ void SelectionDAGBuilder::visitLoad(const LoadInst &I) {
 
   bool isVolatile = I.isVolatile();
   bool isNonTemporal = I.getMetadata(LLVMContext::MD_nontemporal) != nullptr;
-
-  // The IR notion of invariant_load only guarantees that all *non-faulting*
-  // invariant loads result in the same value.  The MI notion of invariant load
-  // guarantees that the load can be legally moved to any location within its
-  // containing function.  The MI notion of invariant_load is stronger than the
-  // IR notion of invariant_load -- an MI invariant_load is an IR invariant_load
-  // with a guarantee that the location being loaded from is dereferenceable
-  // throughout the function's lifetime.
-
-  bool isInvariant = I.getMetadata(LLVMContext::MD_invariant_load) != nullptr &&
-                     isDereferenceablePointer(SV, DAG.getDataLayout());
+  bool isInvariant = I.getMetadata(LLVMContext::MD_invariant_load) != nullptr;
+  bool isDereferenceable = isDereferenceablePointer(SV, DAG.getDataLayout());
   unsigned Alignment = I.getAlignment();
 
   AAMDNodes AAInfo;
@@ -3551,6 +3543,8 @@ void SelectionDAGBuilder::visitLoad(const LoadInst &I) {
       MMOFlags |= MachineMemOperand::MONonTemporal;
     if (isInvariant)
       MMOFlags |= MachineMemOperand::MOInvariant;
+    if (isDereferenceable)
+      MMOFlags |= MachineMemOperand::MODereferenceable;
 
     SDValue L = DAG.getLoad(ValueVTs[i], dl, Root, A,
                             MachinePointerInfo(SV, Offsets[i]), Alignment,