[Mlir-commits] [mlir] [mlir-tblgen] Emit named operand indices (PR #146839)

[Michael Kruse]

https://github.com/Meinersbur created https://github.com/llvm/llvm-project/pull/146839

An operation's operands are defined by the `arguments` field in the tablegen definition. mlir-tblgen generates accessors for them: `getXYZ()` and `setXYZ(...)` to set an operation's operands without knowing the operand's index, but it does not expose the operand index itself. Yet some use cases requires knowing the operand index that is now covered by just getters and setters. For instance:
 * Given an `mlir::OpOperand`, find out whether it is a specific argument (from the `arguments` field in the `.td` file)
 * For operation with variable number of operands (variadic, `AttrSizedOperandSegments`), get the value to pass to `getODSOperands` or `getODSOperandIndexAndLength`.

Emitting a named constant avoids hardcoding the index in the source as magic constant, such as `2` in https://github.com/llvm/llvm-project/blob/d56c06e6c9f0cf03d75fd755c099a6844ecf38e6/mlir/lib/Dialect/LLVMIR/IR/NVVMDialect.cpp#L244

Extracted out of #144785

>From 4a18faad39910ea4d4b66185ba25488ea905e019 Mon Sep 17 00:00:00 2001
From: Michael Kruse <llvm-project at meinersbur.de>
Date: Thu, 3 Jul 2025 10:51:55 +0200
Subject: [PATCH] Emit named operand indices

---
 mlir/test/mlir-tblgen/op-operand.td         | 11 +++++++++++
 mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp | 11 +++++++++++
 2 files changed, 22 insertions(+)

diff --git a/mlir/test/mlir-tblgen/op-operand.td b/mlir/test/mlir-tblgen/op-operand.td
index a2fa1f7046a97..ab8d721ed5427 100644
--- a/mlir/test/mlir-tblgen/op-operand.td
+++ b/mlir/test/mlir-tblgen/op-operand.td
@@ -13,6 +13,9 @@ def OpA : NS_Op<"one_normal_operand_op", []> {
   let arguments = (ins I32:$input);
 }
 
+// DECL-LABEL: class OpA : {{.*}} {
+// DECL: static constexpr int odsIndex_input = 0;
+
 // CHECK-LABEL: OpA definitions
 
 // CHECK:      void OpA::build
@@ -28,6 +31,9 @@ def OpB : NS_Op<"one_variadic_operand_op", []> {
   let arguments = (ins Variadic<I32>:$input);
 }
 
+// DECL-LABEL: class OpB : {{.*}} {
+// DECL: static constexpr int odsIndex_input = 0;
+
 // CHECK-LABEL: OpB::build
 // CHECK:         ::mlir::ValueRange input
 // CHECK-NOT:     assert
@@ -37,6 +43,11 @@ def OpD : NS_Op<"mix_variadic_and_normal_inputs_op", [SameVariadicOperandSize]>
   let arguments = (ins Variadic<AnyTensor>:$input1, AnyTensor:$input2, Variadic<AnyTensor>:$input3);
 }
 
+// DECL-LABEL: class OpD : {{.*}} {
+// DECL: static constexpr int odsIndex_input1 = 0;
+// DECL: static constexpr int odsIndex_input2 = 1;
+// DECL: static constexpr int odsIndex_input3 = 2;
+
 // DECL-LABEL: ::mlir::Operation::operand_range getInput1
 // DECL-NEXT: return getODSOperands(0);
 
diff --git a/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp b/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
index 6008ed4673d1b..cbb4030f3adb4 100644
--- a/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
@@ -2223,6 +2223,17 @@ generateNamedOperandGetters(const Operator &op, Class &opClass,
                     "'SameVariadicOperandSize' traits");
   }
 
+  // Print the ods names so they don't need to be hardcoded in the source.
+  for (int i = 0; i != numOperands; ++i) {
+    const auto &operand = op.getOperand(i);
+    if (operand.name.empty())
+      continue;
+
+    opClass.declare<Field>("static constexpr int", Twine("odsIndex_") +
+                                                       operand.name + " = " +
+                                                       Twine(i));
+  }
+
   // First emit a few "sink" getter methods upon which we layer all nicer named
   // getter methods.
   // If generating for an adaptor, the method is put into the non-templated