[llvm] [RFC] TableGen-erate SDNode descriptions (PR #119709)

[Sergei Barannikov via llvm-commits]

================
@@ -688,22 +687,6 @@ END_TWO_BYTE_PACK()
   /// \<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
-  /// opcode are currently automatically considered to possibly raise
-  /// FP exceptions as well.
-  bool isTargetStrictFPOpcode() const {
-    return NodeType >= ISD::FIRST_TARGET_STRICTFP_OPCODE;
-  }
-
-  /// Test if this node has a target-specific
-  /// memory-referencing opcode (in the \<target\>ISD namespace and
-  /// greater than FIRST_TARGET_MEMORY_OPCODE).
-  bool isTargetMemoryOpcode() const {
----------------
s-barannikov wrote:

I remembered it has one more "use". Before this patch it is implicitly checked [here](https://github.com/llvm/llvm-project/blob/73731d6873b6fb0757c3065aaf2452eaccd0eebc/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp#L4398). `isTargetStrictFPOpcode` returns true for memory opcodes as well. `mayRaiseFPException` is then used [here](https://github.com/llvm/llvm-project/blob/73731d6873b6fb0757c3065aaf2452eaccd0eebc/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp#L4227) to decide whether the resulting MachineInstr needs `NoFPExcept` flag. IIUC it will *not* set this flag on MachineInstrs if the matched SDNode(s) are flagged as memory accessing.

This behavior was introduced in 63336795. I couldn't conclude if it is safe to return false for memory opcodes so I left it as is.

After this patch the check is explicit, please see `SelectionDAGTargetInfo.cpp:mayRaiseFPException`.


https://github.com/llvm/llvm-project/pull/119709