[libomptarget] Implement smid for amdgcn

[JonChesterfield]

Summary

[libomptarget] Implement smid for amdgcn

Implementation is in a new file as it uses an intrinsic with
complicated encoding that warranted substantial comments.

[jdoerfert]

LGTM, I mean it is black magic but that is to be expected. One comment below.

openmp/libomptarget/deviceRTLs/amdgcn/src/amdgcn_smid.hip

57

I would prefer these to be ENUMs with documentation instead of defines. I would also opt for // comments instead.

Other than that I just believe you this does something useful.

[JonChesterfield]

• address review comments

[JonChesterfield]

Change comment style and defines to enum values, thanks. Also extended the documentation a little. The more clues we can give our future selves here the better.

openmp/libomptarget/deviceRTLs/amdgcn/CMakeLists.txt

if(LIBOMPTARGET_NVPTX_DEBUG)
   set(CUDA_DEBUG -DOMPTARGET_NVPTX_DEBUG=-1)
 endif()
 
 get_filename_component(devicertl_base_directory
   ${CMAKE_CURRENT_SOURCE_DIR}
   DIRECTORY)
 
 set(cuda_sources
+  ${CMAKE_CURRENT_SOURCE_DIR}/src/amdgcn_smid.hip
   ${CMAKE_CURRENT_SOURCE_DIR}/src/target_impl.hip
   ${devicertl_base_directory}/common/src/cancel.cu
   ${devicertl_base_directory}/common/src/critical.cu
   ${devicertl_base_directory}/common/src/data_sharing.cu
   ${devicertl_base_directory}/common/src/libcall.cu
   ${devicertl_base_directory}/common/src/loop.cu
   ${devicertl_base_directory}/common/src/omp_data.cu
   ${devicertl_base_directory}/common/src/omptarget.cu

openmp/libomptarget/deviceRTLs/amdgcn/src/amdgcn_smid.hip

+//===-------- amdgcn_smid.hip - AMDGCN smid implementation -------- HIP -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "target_impl.h"
+
+// Partially derived fom hcc_detail/device_functions.h
+
+// HW_ID Register bit structure
+// WAVE_ID     3:0     Wave buffer slot number. 0-9.
+// SIMD_ID     5:4     SIMD which the wave is assigned to within the CU.
+// PIPE_ID     7:6     Pipeline from which the wave was dispatched.
+// CU_ID       11:8    Compute Unit the wave is assigned to.
+// SH_ID       12      Shader Array (within an SE) the wave is assigned to.
+// SE_ID       14:13   Shader Engine the wave is assigned to.
+// TG_ID       19:16   Thread-group ID
+// VM_ID       23:20   Virtual Memory ID
+// QUEUE_ID    26:24   Queue from which this wave was dispatched.
+// STATE_ID    29:27   State ID (graphics only, not compute).
+// ME_ID       31:30   Micro-engine ID.
+
+enum {
+  HW_ID = 4, // specify that the hardware register to read is HW_ID
+
+  HW_ID_CU_ID_SIZE = 4,   // size of CU_ID field in bits
+  HW_ID_CU_ID_OFFSET = 8, // offset of CU_ID from start of register
+
+  HW_ID_SE_ID_SIZE = 2,    // sizeof SE_ID field in bits
+  HW_ID_SE_ID_OFFSET = 13, // offset of SE_ID from start of register
+};
+
+// The s_getreg_b32 instruction, exposed as an intrinsic, takes a 16 bit
+// immediate and returns a 32 bit value.
+// The encoding of the immediate parameter is:
+// ID           5:0     Which register to read from
+// OFFSET       10:6    Range: 0..31
+// WIDTH        15:11   Range: 1..32
+
+// The asm equivalent is s_getreg_b32 %0, hwreg(HW_REG_HW_ID, Offset, Width)
+// where hwreg forms a 16 bit immediate encoded by the assembler thus:
+// uint64_t encodeHwreg(uint64_t Id, uint64_t Offset, uint64_t Width) {
+//   return (Id << 0_) | (Offset << 6) | ((Width - 1) << 11);
+// }
+#define ENCODE_HWREG(WIDTH, OFF, REG) (REG | (OFF << 6) | ((WIDTH - 1) << 11))
+
+// Note: The results can be changed by a context switch
+// Return value in [0 2^SE_ID_SIZE * 2^CU_ID_SIZE), which is an upper
+// bound on how many compute units are available. Some values in this
+// range may never be returned if there are fewer than 2^CU_ID_SIZE CUs.
+
+DEVICE uint32_t __kmpc_impl_smid() {
+  uint32_t cu_id = __builtin_amdgcn_s_getreg(
+      ENCODE_HWREG(HW_ID_CU_ID_SIZE, HW_ID_CU_ID_OFFSET, HW_ID));
+  uint32_t se_id = __builtin_amdgcn_s_getreg(
+      ENCODE_HWREG(HW_ID_SE_ID_SIZE, HW_ID_SE_ID_OFFSET, HW_ID));
+  return (se_id << HW_ID_CU_ID_SIZE) + cu_id;
+}