[MLIR][LLVM] Add MemRead/MemWrite behavior to llvm store/load/addressof ops

[wsmoses]

Summary

This patch adds corresponding memory effects to mlir llvm-dialect load/store/addressof ops, which thus enables canonicalizations of those ops (like dead code elimination) that rely on the effect interface

[wsmoses]

Add Addressof Op

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

def LLVM_GEPOp : LLVM_Op<"getelementptr", [NoSideEffect]> {
   }];
   let hasFolder = 1;
   let verifier = [{
     return ::verify(*this);
   }];
 }
 
 def LLVM_LoadOp : LLVM_Op<"load">, MemoryOpWithAlignmentAndAttributes {
-  let arguments = (ins LLVM_PointerTo<LLVM_LoadableType>:$addr,
+  let arguments = (ins Arg<LLVM_PointerTo<LLVM_LoadableType>, "", [MemRead]>:$addr,
                    OptionalAttr<SymbolRefArrayAttr>:$access_groups,
                    OptionalAttr<SymbolRefArrayAttr>:$alias_scopes,
                    OptionalAttr<SymbolRefArrayAttr>:$noalias_scopes,
                    OptionalAttr<I64Attr>:$alignment, UnitAttr:$volatile_,
                    UnitAttr:$nontemporal);
   let results = (outs LLVM_LoadableType:$res);
   string llvmBuilder = [{
     auto *inst = builder.CreateLoad(
OpBuilder<(ins "Type":$t, "Value":$addr,
       CArg<"bool", "false">:$isNonTemporal)>];
   let parser = [{ return parseLoadOp(parser, result); }];
   let printer = [{ printLoadOp(p, *this); }];
   let verifier = [{ return ::verify(*this);  }];
 }
 
 def LLVM_StoreOp : LLVM_Op<"store">, MemoryOpWithAlignmentAndAttributes {
   let arguments = (ins LLVM_LoadableType:$value,
-                   LLVM_PointerTo<LLVM_LoadableType>:$addr,
+                   Arg<LLVM_PointerTo<LLVM_LoadableType>,"",[MemWrite]>:$addr,
                    OptionalAttr<SymbolRefArrayAttr>:$access_groups,
                    OptionalAttr<SymbolRefArrayAttr>:$alias_scopes,
                    OptionalAttr<SymbolRefArrayAttr>:$noalias_scopes,
                    OptionalAttr<I64Attr>:$alignment, UnitAttr:$volatile_,
                    UnitAttr:$nontemporal);
   string llvmBuilder = [{
     auto *inst = builder.CreateStore($value, $addr, $volatile_);
   }] # setAlignmentCode

mlir/test/Dialect/LLVMIR/canonicalize.mlir

func @llvm_constant() -> i32 {
   %0 = llvm.mlir.constant(40 : i32) : i32
   %1 = llvm.mlir.constant(42 : i32) : i32
   // CHECK: %[[RES:.*]] = arith.constant 82 : i32
   // CHECK-NOT: arith.addi
   %2 = arith.addi %0, %1 : i32
   // CHECK: return %[[RES]]
   return %2 : i32
 }
+
+// -----
+
+// CHECK-LABEL: load_dce
+// CHECK-NEXT: llvm.return
+llvm.func @load_dce(%x : !llvm.ptr<i8>) {
+  %0 = llvm.load %x : !llvm.ptr<i8>
+  llvm.return 
+}