Subzero: Transform suitable Load/Arith/Store sequences into RMW ops.

src/IceCfg.cpp

 //===- subzero/src/IceCfg.cpp - Control flow graph implementation ---------===//
 //
 //                        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 Cfg class, including constant pool
@@ skipping 415 matching lines @@
     if (Mode == Liveness_Intervals) {
       // Special treatment for live in-args.  Their liveness needs to
       // extend beyond the beginning of the function, otherwise an arg
       // whose only use is in the first instruction will end up having
       // the trivial live range [2,2) and will *not* interfere with
       // other arguments.  So if the first instruction of the method
       // is "r=arg1+arg2", both args may be assigned the same
       // register.  This is accomplished by extending the entry
       // block's instruction range from [2,n) to [1,n) which will
       // transform the problematic [2,2) live ranges into [1,2).
-      if (FirstInstNum == Inst::NumberInitial)
+      if (Node == getEntryNode()) {
+        // TODO(stichnot): Make it a strict requirement that the entry
+        // node gets the lowest instruction numbers, so that extending
+        // the live range for in-args is guaranteed to work.
         FirstInstNum = Inst::NumberExtended;
+      }
       Node->livenessAddIntervals(getLiveness(), FirstInstNum, LastInstNum);
     }
   }
 }
 
 // Traverse every Variable of every Inst and verify that it
 // appears within the Variable's computed live range.
 bool Cfg::validateLiveness() const {
   TimerMarker T(TimerStack::TT_validateLiveness, this);
   bool Valid = true;
@@ skipping 167 matching lines @@
     }
   }
   // Print each basic block
   for (CfgNode *Node : Nodes)
     Node->dump(this);
   if (isVerbose(IceV_Instructions))
     Str << "}\n";
 }
 
 } // end of namespace Ice