Subzero: Apply commutativity to the RMW optimization.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the TargetLoweringX8632 class, which
@@ skipping 671 matching lines @@
             // RMW instruction is ignored during lowering because it is
             // redundant with the Store instruction.
             //
             // Note that if "a" has further uses, the RMW transformation may
             // still trigger, resulting in two loads and one store, which is
             // worse than the original one load and one store.  However, this is
             // probably rare, and caching probably keeps it just as fast.
             if (!isSameMemAddressOperand(Load->getSourceAddress(),
                                          Store->getAddr()))
               continue;
-            if (false && Load->getSourceAddress() != Store->getAddr())
-              continue;
-            if (Arith->getSrc(0) != Load->getDest())
-              continue;
+            Operand *ArithSrcFromLoad = Arith->getSrc(0);
+            Operand *ArithSrcOther = Arith->getSrc(1);
+            if (ArithSrcFromLoad != Load->getDest()) {
+              if (!Arith->isCommutative() || ArithSrcOther != Load->getDest())
+                continue;
+              std::swap(ArithSrcFromLoad, ArithSrcOther);
+            }
             if (Arith->getDest() != Store->getData())
               continue;
             if (!canRMW(Arith))
               continue;
             if (Func->isVerbose(IceV_RMW)) {
               Str << "Found RMW in " << Func->getFunctionName() << ":\n  ";
               Load->dump(Func);
               Str << "\n  ";
               Arith->dump(Func);
               Str << "\n  ";
               Store->dump(Func);
               Str << "\n";
             }
             Variable *Beacon = Func->makeVariable(IceType_i32);
             Beacon->setWeight(0);
             Store->setRmwBeacon(Beacon);
             InstFakeDef *BeaconDef = InstFakeDef::create(Func, Beacon);
             Node->getInsts().insert(I3, BeaconDef);
             InstX8632FakeRMW *RMW = InstX8632FakeRMW::create(
-                Func, Arith->getSrc(1), Store->getAddr(), Beacon,
-                Arith->getOp());
+                Func, ArithSrcOther, Store->getAddr(), Beacon, Arith->getOp());
             Node->getInsts().insert(I3, RMW);
           }
         }
       }
     }
   }
 }
 
 namespace {
 
@@ skipping 4618 matching lines @@
     emitConstantPool<PoolTypeConverter<float>>(Ctx);
     emitConstantPool<PoolTypeConverter<double>>(Ctx);
   } break;
   }
 }
 
 TargetHeaderX8632::TargetHeaderX8632(GlobalContext *Ctx)
     : TargetHeaderLowering(Ctx) {}
 
 } // end of namespace Ice