Set the stack alignment to 64 bytes for x86 microkernel builds.

This makes register spilling a _lot_ faster in some cases where the stack pointer was not aligned.

Note that the baseline stack alignment depends on the size and alignment of the underlying call stack and may therefore vary significantly from one type of benchmark to another.

PiperOrigin-RevId: 719315622

CMakeLists.txt

@@ -965,6 +965,13 @@ IF(XNNPACK_TARGET_PROCESSOR MATCHES "^x86(_64)?$")
       SET_PROPERTY(SOURCE ${ALL_AVX512AMX_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -clang:-mf16c -clang:-mfma -clang:-mavx512f -clang:-mavx512cd -clang:-mavx512bw -clang:-mavx512dq -clang:-mavx512vl -clang:-mavx512vnni -clang:-mgfni -clang:-mamx-tile -clang:-mamx-int8 ")
     ENDIF()
   ELSE()
+    IF(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+      SET_PROPERTY(SOURCE ${ALL_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -mpreferred-stack-boundary=6 -fomit-frame-pointer -mstackrealign -mincoming-stack-boundary=4 ")
+    ELSEIF(CMAKE_C_COMPILER_ID STREQUAL "Clang")
+      SET_PROPERTY(SOURCE ${ALL_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -mstack-alignment=64 -fomit-frame-pointer -mstackrealign")
+    ELSE()
+      SET_PROPERTY(SOURCE ${ALL_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -fomit-frame-pointer ")
+    ENDIF()
     SET_PROPERTY(SOURCE ${ALL_SSE_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -msse -mno-sse2 ")
     SET_PROPERTY(SOURCE ${ALL_SSE2_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -msse2 -mno-sse3 ")
     SET_PROPERTY(SOURCE ${ALL_SSSE3_MICROKERNEL_SRCS} APPEND_STRING PROPERTY COMPILE_FLAGS " -mssse3 -mno-sse4.1 ")

build_config/BUILD.bazel

@@ -262,6 +262,20 @@ config_setting(
     },
 )
 
+config_setting(
+    name = "clang",
+    flag_values = {
+        "@bazel_tools//tools/cpp:compiler": "clang",
+    },
+)
+
+config_setting(
+    name = "gcc",
+    flag_values = {
+        "@bazel_tools//tools/cpp:compiler": "gcc",
+    },
+)
+
 ######################## Composite build configurations #######################
 
 selects.config_setting_group(
@@ -334,3 +348,19 @@ selects.config_setting_group(
     name = "riscv",
     match_any = [":linux_riscv64"],
 )
+
+selects.config_setting_group(
+    name = "x86_clang",
+    match_all = [
+        ":x86",
+        ":clang",
+    ],
+)
+
+selects.config_setting_group(
+    name = "x86_gcc",
+    match_all = [
+        ":x86",
+        ":gcc",
+    ],
+)

build_params.bzl

@@ -209,6 +209,17 @@ def xnnpack_cc_library_for_arch(arch, name, deps = None, **kwargs):
         else:
             kwargs[key] = val
 
+    # Add extra copts.
+    copts = select({
+        "//build_config:x86_clang": ["-mstack-alignment=64", "-fomit-frame-pointer", "-mstackrealign"],
+        "//build_config:x86_gcc": ["-mpreferred-stack-boundary=6", "-fomit-frame-pointer", "-mstackrealign", "-mincoming-stack-boundary=4"],
+        "//conditions:default": [],
+    })
+    if "copts" in kwargs:
+        kwargs["copts"] += copts
+    else:
+        kwargs["copts"] = copts
+
     xnnpack_cc_library(
         name = name,
         target_compatible_with = xnnpack_select_if(