[SelectionDAG] Use consistent type sizes for opcode

[mbrkusanin]

Not sure if I picked the right reviewers.
A downstream target broke because it exceeded 32768 opcodes.

[RKSimon]

Are you seeing much change in memory usage?

[arsenm]

What is sizeof(SDNode) before and after?

[mbrkusanin]

I ran a test with 100 fadd float instructions ('-debug' reported 106 nodes) and measured memory with '--time-passes -track-memory' option.
There were small differences in reported memory between runs (not sure what is the reason for this).
Here are the results for 10 runs for 'AMDGPU DAG->DAG Pattern Instruction Selection' pass:

int16_t

205696
204768
204816
206528
206528
205696
205696
205648
206528
204816

avg = 205672

int32_t

209808
209808
210640
209760
209808
209808
210640
209808
210640
209808

avg = 210052.8

increase:
210052.8 / 205672 = 1.0212999338753

Other passes were mostly indentical with small variations between runs.

sizeof(SDNode) went from 88 to 96.

[foad]

In D135453#3852611, @mbrkusanin wrote:

sizeof(SDNode) went from 88 to 96.

NodeType and NodeBitfields are supposed to pack into a 32-bit word. Maybe you could swap "uint16_t PersistentId;" to the start of the struct instead, and pack that with the NodeBitfields, to avoid increasing the size?

[mbrkusanin]

In D135453#3852683, @foad wrote:

In D135453#3852611, @mbrkusanin wrote:

sizeof(SDNode) went from 88 to 96.

NodeType and NodeBitfields are supposed to pack into a 32-bit word. Maybe you could swap "uint16_t PersistentId;" to the start of the struct instead, and pack that with the NodeBitfields, to avoid increasing the size?

Great idea. That works. SDNode size is now 88.

'--time-passes -track-memory' now looks identical.

[foad]

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

477

"with PersistentId"

[mbrkusanin]

• Updated comment.

[mbrkusanin]

8b8463ef6c6d487e771b577ccd08e6c684d97690

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

public:
   }
 };
 
 /// Represents one node in the SelectionDAG.
 ///
 class SDNode : public FoldingSetNode, public ilist_node<SDNode> {
 private:
   /// The operation that this node performs.
-  int16_t NodeType;
+  int32_t NodeType;
+
+public:
+  /// Unique and persistent id per SDNode in the DAG. Used for debug printing.
+  /// We do not place that under `#if LLVM_ENABLE_ABI_BREAKING_CHECKS`
+  /// intentionally because it adds unneeded complexity without noticeable
+  /// benefits (see discussion with @thakis in D120714).
+  uint16_t PersistentId;
 
 protected:
   // We define a set of mini-helper classes to help us interpret the bits in our
   // SubclassData.  These are designed to fit within a uint16_t so they pack
-  // with NodeType.
+  // with PersistentId.
 
 #if defined(_AIX) && (!defined(__GNUC__) || defined(__clang__))
 // Except for GCC; by default, AIX compilers store bit-fields in 4-byte words
 // and give the `pack` pragma push semantics.
 #define BEGIN_TWO_BYTE_PACK() _Pragma("pack(2)")
 #define END_TWO_BYTE_PACK() _Pragma("pack(pop)")
 #else
 #define BEGIN_TWO_BYTE_PACK()
private:
   /// Return a pointer to the specified value type.
   static const EVT *getValueTypeList(EVT VT);
 
   SDNodeFlags Flags;
 
   uint32_t CFIType = 0;
 
 public:
-  /// Unique and persistent id per SDNode in the DAG. Used for debug printing.
-  /// We do not place that under `#if LLVM_ENABLE_ABI_BREAKING_CHECKS`
-  /// intentionally because it adds unneeded complexity without noticeable
-  /// benefits (see discussion with @thakis in D120714).
-  uint16_t PersistentId;
-
   //===--------------------------------------------------------------------===//
   //  Accessors
   //
 
   /// Return the SelectionDAG opcode value for this node. For
   /// pre-isel nodes (those for which isMachineOpcode returns false), these
   /// are the opcode values in the ISD and <target>ISD namespaces. For
   /// post-isel opcodes, see getMachineOpcode.
-  unsigned getOpcode()  const { return (unsigned short)NodeType; }
+  unsigned getOpcode()  const { return (unsigned)NodeType; }
 
   /// Test if this node has a target-specific opcode (in the
   /// \<target\>ISD namespace).
   bool isTargetOpcode() const { return NodeType >= ISD::BUILTIN_OP_END; }
 
   /// Test if this node has a target-specific opcode that may raise
   /// FP exceptions (in the \<target\>ISD namespace and greater than
   /// FIRST_TARGET_STRICTFP_OPCODE).  Note that all target memory

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

 static void AddNodeIDOperands(FoldingSetNodeID &ID,
                               ArrayRef<SDUse> Ops) {
   for (const auto &Op : Ops) {
     ID.AddPointer(Op.getNode());
     ID.AddInteger(Op.getResNo());
   }
 }
 
-static void AddNodeIDNode(FoldingSetNodeID &ID, unsigned short OpC,
+static void AddNodeIDNode(FoldingSetNodeID &ID, unsigned OpC,
                           SDVTList VTList, ArrayRef<SDValue> OpList) {
   AddNodeIDOpcode(ID, OpC);
   AddNodeIDValueTypes(ID, VTList);
   AddNodeIDOperands(ID, OpList);
 }
 
 /// If this is an SDNode with special info, add this info to the NodeID data.
 static void AddNodeIDCustom(FoldingSetNodeID &ID, const SDNode *N) {