[CGP] Separate Select and Phi case in optimizeMemoryInst

[skatkov]

Summary

This patch is a preparation for "Extends the scope of optimizeMemoryInst optimization".

It just a NFC to separate combining of Select and Phi nodes.

[john.brawn]

lib/CodeGen/CodeGenPrepare.cpp

4630

You could instead figure out if we have a select or phi by passing through Addr and checking its type. Or alternatively attach the select/phi to each ExtAddrMode that came from it (similar to what D38133 does with AddrModeUser) and examine the type of that.

[skatkov]

No need for this restriction...

lib/CodeGen/CodeGenPrepare.cpp

if (DifferentField != ExtAddrMode::MultipleFields) {
       return true;
     }
 
     // We couldn't combine NewAddrMode with the rest, so return failure.
     AddrModes.clear();
     return false;
   }
 
+  /// \brief Defines how to combine AddrModes.
+  enum CombineType {
+    // All AddrModes are direct input of Select instruction.
+    // The new Select instruction will be created to combine the
+    // values of difference between AddrModes.
+    CombineBySelect,
+    // All AddrModes are accessible to origin Addr through only Phi nodes
+    // or there is only one AddrMode.
+    CombineByPhi
+  };
+
   /// \brief Combine the addressing modes we've collected into a single
   /// addressing mode. OnlySingleAddrMode means that only single AddrMode
   /// can be combined.
   /// \return True iff we successfully combined them or we only had one so
   /// didn't need to combine them anyway.
-  bool combineAddrModes(bool OnlySingleAddrMode) {
+  bool combineAddrModes(bool OnlySingleAddrMode, CombineType Type) {
     // If we have no AddrModes then they can't be combined.
     if (AddrModes.size() == 0)
       return false;
 
     // A single AddrMode can trivially be combined.
     if (AddrModes.size() == 1)
       return true;
 
     // If we cannot process other than single AddrMode, bail out now.
     if (OnlySingleAddrMode)
       return false;
 
     // If the AddrModes we collected are all just equal to the value they are
     // derived from then combining them wouldn't do anything useful.
     if (AllAddrModesTrivial)
       return false;
 
-    // TODO: Combine multiple AddrModes by inserting a select or phi for the
+    // Combine multiple AddrModes by inserting a select or phi for the
     // field in which the AddrModes differ.
+    if (Type == CombineBySelect) {
+      return combineBySelect();
+    } else {
+      assert(Type == CombineByPhi && "Unexpected combine type!");
+      return combineByPhi();
+    }
+  }
+
+  bool combineBySelect() {
+    assert(AddrModes.size() == 2 && "Too many AddrModes for Select");
+    // TODO: Create select basing on AddrModes.
+    return false;
+  }
+
+  bool combineByPhi() {
+    // The first version supports only combine by base register.
+    if (DifferentField != ExtAddrMode::BaseRegField)
+      return false;
+    // TODO: Find/Create Phi node combining the difference between AddrModes.
     return false;
   }
 };
 
 } // end anonymous namespace
 
 /// Try adding ScaleReg*Scale to the current addressing mode.
 /// Return true and update AddrMode if this addr mode is legal for the target,
bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
   bool OnlySingleAddrMode = CountPhiSeen && CountSelectSeen;
   // If we saw two selects we support only one AddrMode now.
   if (!OnlySingleAddrMode)
     OnlySingleAddrMode = CountSelectSeen > 1;
 
   // Try to combine the AddrModes we've collected. If we couldn't collect any,
   // or we have multiple but either couldn't combine them or combining them
   // wouldn't do anything useful, bail out now.
-  if (!AddrModes.combineAddrModes(OnlySingleAddrMode)) {
+  auto CombineType = CountSelectSeen ? AddressingModeCombiner::CombineBySelect
+                                     : AddressingModeCombiner::CombineByPhi;
+  if (!AddrModes.combineAddrModes(OnlySingleAddrMode, CombineType)) {
     TPT.rollback(LastKnownGood);
     return false;
   }
   TPT.commit();
 
   // Get the combined AddrMode (or the only AddrMode, if we only had one).
   ExtAddrMode AddrMode = AddrModes.getAddrMode();