Reland "[CodeGen] Make logic of CCState::resultsCompatible clearer"

This relands commit d782d1f.
With a typo fixed, which was causing the x86 test failure.

llvm/lib/CodeGen/CallingConvLower.cpp

@@ -276,18 +276,14 @@ bool CCState::resultsCompatible(CallingConv::ID CalleeCC,
   for (unsigned I = 0, E = RVLocs1.size(); I != E; ++I) {
     const CCValAssign &Loc1 = RVLocs1[I];
     const CCValAssign &Loc2 = RVLocs2[I];
-    if (Loc1.getLocInfo() != Loc2.getLocInfo())
-      return false;
-    bool RegLoc1 = Loc1.isRegLoc();
-    if (RegLoc1 != Loc2.isRegLoc())
+
+    if ( // Must both be in registers, or both in memory
+        Loc1.isRegLoc() != Loc2.isRegLoc() ||
+        // Must fill the same part of their locations
+        Loc1.getLocInfo() != Loc2.getLocInfo() ||
+        // Memory offset/register number must be the same
+        Loc1.getExtraInfo() != Loc2.getExtraInfo())
       return false;
-    if (RegLoc1) {
-      if (Loc1.getLocReg() != Loc2.getLocReg())
-        return false;
-    } else {
-      if (Loc1.getLocMemOffset() != Loc2.getLocMemOffset())
-        return false;
-    }
   }
   return true;
 }