[Mlir-commits] [mlir] [mlir][Python] don't build libnanobind if module only has "pure" extensions (PR #175090)

[Maksim Levental]

https://github.com/makslevental updated https://github.com/llvm/llvm-project/pull/175090

>From ddbdae79711b7ead2249ab7a3540ce153e6c1cc7 Mon Sep 17 00:00:00 2001
From: makslevental <maksim.levental at gmail.com>
Date: Thu, 8 Jan 2026 15:19:12 -0800
Subject: [PATCH 1/2] [mlir][Python] don't build libnanobind if module only has
 "pure" extensions

---
 mlir/cmake/modules/AddMLIRPython.cmake | 28 +++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/mlir/cmake/modules/AddMLIRPython.cmake b/mlir/cmake/modules/AddMLIRPython.cmake
index f4d078dfe7118..ba3f8de8512eb 100644
--- a/mlir/cmake/modules/AddMLIRPython.cmake
+++ b/mlir/cmake/modules/AddMLIRPython.cmake
@@ -393,13 +393,28 @@ function(add_mlir_python_modules name)
     set(ARG_MLIR_BINDINGS_PYTHON_NB_DOMAIN "mlir")
   endif()
 
+  # Collect up all the transitive extension targets.
+  _flatten_mlir_python_targets(_flat_targets ${ARG_DECLARED_SOURCES})
+
+  # Modules with only pure extensions shouldn't build libnanobind.
+  set(_needs_build_nanobind_lib OFF)
+  foreach(sources_target ${_flat_targets})
+    get_target_property(_source_type ${sources_target} mlir_python_SOURCES_TYPE)
+    if((_source_type STREQUAL "support") OR (_source_type STREQUAL "extension"))
+      set(_needs_build_nanobind_lib ON)
+      break()
+    endif()
+  endforeach()
+
   # This call sets NB_LIBRARY_TARGET_NAME.
-  build_nanobind_lib(
-    INSTALL_COMPONENT ${name}
-    INSTALL_DESTINATION "${ARG_INSTALL_PREFIX}/_mlir_libs"
-    OUTPUT_DIRECTORY "${ARG_ROOT_PREFIX}/_mlir_libs"
-    MLIR_BINDINGS_PYTHON_NB_DOMAIN ${ARG_MLIR_BINDINGS_PYTHON_NB_DOMAIN}
-  )
+  if(_needs_build_nanobind_lib)
+    build_nanobind_lib(
+      INSTALL_COMPONENT ${name}
+      INSTALL_DESTINATION "${ARG_INSTALL_PREFIX}/_mlir_libs"
+      OUTPUT_DIRECTORY "${ARG_ROOT_PREFIX}/_mlir_libs"
+      MLIR_BINDINGS_PYTHON_NB_DOMAIN ${ARG_MLIR_BINDINGS_PYTHON_NB_DOMAIN}
+    )
+  endif()
 
   # Helper to process an individual target.
   function(_process_target modules_target sources_target support_libs)
@@ -442,7 +457,6 @@ function(add_mlir_python_modules name)
 
   # Build the modules target.
   add_custom_target(${name} ALL)
-  _flatten_mlir_python_targets(_flat_targets ${ARG_DECLARED_SOURCES})
 
   # Build all support libs first.
   set(_mlir_python_support_libs)

>From 7a6430200fb9441fabe9091fbf22cd4f66b2bef0 Mon Sep 17 00:00:00 2001
From: Maksim Levental <maksim.levental at gmail.com>
Date: Mon, 12 Jan 2026 08:49:20 -0800
Subject: [PATCH 2/2] Update mlir/cmake/modules/AddMLIRPython.cmake

Co-authored-by: Rahul Kayaith <rkayaith at amd.com>
---
 mlir/cmake/modules/AddMLIRPython.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mlir/cmake/modules/AddMLIRPython.cmake b/mlir/cmake/modules/AddMLIRPython.cmake
index ba3f8de8512eb..acc85e5fa6b02 100644
--- a/mlir/cmake/modules/AddMLIRPython.cmake
+++ b/mlir/cmake/modules/AddMLIRPython.cmake
@@ -396,7 +396,7 @@ function(add_mlir_python_modules name)
   # Collect up all the transitive extension targets.
   _flatten_mlir_python_targets(_flat_targets ${ARG_DECLARED_SOURCES})
 
-  # Modules with only pure extensions shouldn't build libnanobind.
+  # Modules with only pure python extensions shouldn't build libnanobind.
   set(_needs_build_nanobind_lib OFF)
   foreach(sources_target ${_flat_targets})
     get_target_property(_source_type ${sources_target} mlir_python_SOURCES_TYPE)