Update GEMM (#424)

* Organize and collect metal subroutine templates and elements in `metal/kernels/steel/`
* Update gemm elements for better performance 
* Add split-K specialization for gemm
* Add `addmm` primitive, op and bindings for fused matmul and bias addition 
* Update tests and benchmarks as needed

mlx/backend/metal/kernels/CMakeLists.txt

@@ -18,7 +18,6 @@ set(
   "binary_two"
   "conv"
   "copy"
-  "gemm"
   "gemv"
   "quantized"
   "random"
@@ -30,26 +29,27 @@ set(
   "indexing"
 )
 
-function(build_kernel KERNEL)
-  set(SRCFILE ${CMAKE_CURRENT_SOURCE_DIR}/${KERNEL}.metal)
-  set(HEADERS_PADDED ${HEADERS})
-  if(${KERNEL} STREQUAL "gemm")
-    set(HEADERS_PADDED ${HEADERS_PADDED} ${CMAKE_CURRENT_SOURCE_DIR}/gemm/gemm.h)
-  endif()
-  if(${KERNEL} STREQUAL "conv")
-    set(HEADERS_PADDED ${HEADERS_PADDED} ${CMAKE_CURRENT_SOURCE_DIR}/gemm/conv.h)
-  endif()
+function(build_kernel_base TARGET SRCFILE DEPS)
   add_custom_command(
     COMMAND xcrun -sdk macosx metal -Wall -Wextra
                   -fno-fast-math
                   -c ${SRCFILE} 
                   -I${PROJECT_SOURCE_DIR} 
-                  -o ${KERNEL}.air
-    DEPENDS ${SRCFILE} ${HEADERS_PADDED}
-    OUTPUT ${KERNEL}.air
-    COMMENT "Building ${KERNEL}.air"
+                  -o ${TARGET}.air
+    DEPENDS ${SRCFILE} ${DEPS}
+    OUTPUT ${TARGET}.air
+    COMMENT "Building ${TARGET}.air"
     VERBATIM
   )
+endfunction(build_kernel_base)
+
+function(build_kernel KERNEL)
+  set(SRCFILE ${CMAKE_CURRENT_SOURCE_DIR}/${KERNEL}.metal)
+  set(HEADERS_PADDED ${HEADERS})
+  if(${KERNEL} STREQUAL "conv")
+    set(HEADERS_PADDED ${HEADERS_PADDED} ${CMAKE_CURRENT_SOURCE_DIR}/conv.h)
+  endif()
+  build_kernel_base(${KERNEL} ${SRCFILE} "${HEADERS_PADDED}")
 endfunction(build_kernel)
 
 foreach(KERNEL ${KERNELS})
@@ -57,6 +57,15 @@ foreach(KERNEL ${KERNELS})
   set(KERNEL_AIR ${KERNEL}.air ${KERNEL_AIR})
 endforeach()
 
+file(GLOB_RECURSE STEEL_KERNELS ${CMAKE_CURRENT_SOURCE_DIR}/steel/*.metal)
+file(GLOB_RECURSE STEEL_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/steel/*.h)
+
+foreach(KERNEL ${STEEL_KERNELS})
+  cmake_path(GET KERNEL STEM TARGET)
+  build_kernel_base(${TARGET} ${KERNEL} "${STEEL_HEADERS}")
+  set(KERNEL_AIR ${TARGET}.air ${KERNEL_AIR})
+endforeach()
+
 add_custom_command(
   OUTPUT ${MLX_METAL_PATH}/mlx.metallib
   COMMAND xcrun -sdk macosx metallib ${KERNEL_AIR} -o ${MLX_METAL_PATH}/mlx.metallib