[scons multi_isa] extend multi_isa build to support armv8-a march

This change adds support for multi isa build with armv8-a as the
base micro architecture. To enable this, use 'arch=armv8a' and 'multi_isa=1'
build flags during scons build. This build option doesn't include
fp16 vector arithmetic. To include fp16 vector arithmetic, use 'arch=armv8.2-a'
and 'multi_isa=1' build option.

Signed-off-by: Sunita Nadampalli <nadampal@amazon.com>
Change-Id: Ib5ca61dc65603382baee53b3ec30b2b817beda3c
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/9474
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: SiCong Li <sicong.li@arm.com>
Reviewed-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>

4 files changed, 19 insertions, 9 deletions

diff --git a/SConscript b/SConscript
index 7ea59d2ef3..c774a55d22 100644
--- a/SConscript
+++ b/SConscript
@@ -94,8 +94,12 @@ def build_lib_objects():
                            'ARM_COMPUTE_ENABLE_I8MM', 'ARM_COMPUTE_ENABLE_SVEF32MM'])
 
     # Build all the common files for the base architecture
-    lib_static_objs += build_obj_list(filedefs["armv8.2-a"], lib_files, static=True)
-    lib_shared_objs += build_obj_list(filedefs["armv8.2-a"], lib_files, static=False)
+    if env['arch'] == 'armv8a':
+        lib_static_objs += build_obj_list(filedefs["armv8-a"], lib_files, static=True)
+        lib_shared_objs += build_obj_list(filedefs["armv8-a"], lib_files, static=False)
+    else:
+        lib_static_objs += build_obj_list(filedefs["armv8.2-a"], lib_files, static=True)
+        lib_shared_objs += build_obj_list(filedefs["armv8.2-a"], lib_files, static=False)
 
     # Build the SVE specific files
     lib_static_objs += build_obj_list(filedefs["armv8.2-a-sve"], lib_files_sve, static=True)
diff --git a/SConstruct b/SConstruct
index d6f15c0caf..f6c90c3098 100644
--- a/SConstruct
+++ b/SConstruct
@@ -98,7 +98,7 @@ vars.AddVariables(
     BoolVariable("examples", "Build example programs", True),
     BoolVariable("gemm_tuner", "Build gemm_tuner programs", True),
     BoolVariable("Werror", "Enable/disable the -Werror compilation flag", True),
-    BoolVariable("multi_isa", "Build Multi ISA binary version of library. Note works only for armv8.2-a", False),
+    BoolVariable("multi_isa", "Build Multi ISA binary version of library. Works for armv8a without the support for FP16 vector arithmetic. Use armv8.2-a or beyond to enable FP16 vector arithmetic support", False),
     BoolVariable("standalone", "Builds the tests as standalone executables, links statically with libgcc, libstdc++ and libarm_compute", False),
     BoolVariable("opencl", "Enable OpenCL support", True),
     BoolVariable("neon", "Enable Arm® Neon™ support", False),
@@ -306,11 +306,15 @@ if env['multi_isa']:
         print("Currently Multi ISA binary is only supported for arm v8 family")
         Exit(1)
 
-    if 'v8.6-a' in env['arch']:
-        if "disable_mmla_fp" not in env['custom_options']:
-            env.Append(CPPDEFINES = ['ARM_COMPUTE_ENABLE_SVEF32MM'])
+    if 'v8a' in env['arch']:
+        print("INFO: multi_isa armv8-a architecture build doesn't enable __ARM_FEATURE_FP16_VECTOR_ARITHMETIC. Use armv8.2-a or beyond to enable FP16 vector arithmetic support")
+        env.Append(CXXFLAGS = ['-march=armv8-a']) # note: this will disable fp16 extension __ARM_FEATURE_FP16_VECTOR_ARITHMETIC
+    else:
+        if 'v8.6-a' in env['arch']:
+            if "disable_mmla_fp" not in env['custom_options']:
+                env.Append(CPPDEFINES = ['ARM_COMPUTE_ENABLE_SVEF32MM'])
 
-    env.Append(CXXFLAGS = ['-march=armv8.2-a+fp16']) # explicitly enable fp16 extension otherwise __ARM_FEATURE_FP16_VECTOR_ARITHMETIC is undefined
+        env.Append(CXXFLAGS = ['-march=armv8.2-a+fp16']) # explicitly enable fp16 extension otherwise __ARM_FEATURE_FP16_VECTOR_ARITHMETIC is undefined
 
 else: # NONE "multi_isa" builds
 
diff --git a/docs/user_guide/library.dox b/docs/user_guide/library.dox
index 0501322254..11948d7136 100644
--- a/docs/user_guide/library.dox
+++ b/docs/user_guide/library.dox
@@ -570,7 +570,9 @@ The responsibilities of the operators can be summarized as follows:
 
 Selecting multi_isa when building Compute Library, will create a library that contains all the supported ISA features.
 Based on the CPU support, the appropriate kernel will be selected at runtime for execution. Currently this option is
-only supported with armv8.2-a as the base architecture.
+supported in two configurations: (i) with armv8.2-a as the base architecture where all the supported ISA features are enabled and
+(ii) with armv8-a as the base architecture where only a subset of ISA features (everything except FP16 vector arithmetic)
+are enabled in the build.
 
 @subsection architecture_experimental_per_operator_build Per-operator build
 
diff --git a/filedefs.json b/filedefs.json
index 3422eeb252..8ffa3d9cd9 100644
--- a/filedefs.json
+++ b/filedefs.json
@@ -2,7 +2,7 @@
     "cpu": {
         "arch" : {
             "armv8-a": {
-                "cxxflags": ["-march=armv8.2-a"]
+                "cxxflags": ["-march=armv8-a"]
             },
             "armv8.2-a": {
                 "cxxflags": ["-march=armv8.2-a+fp16"],