[libc] Apply no-builtin everywhere, remove unnecessary flags

Note, this is a re-submission of D125894 with `features = ["-header_modules"]` added to the main BUILD.bazel file. Some functions like `stpncpy` are implemented in terms of `memset` but are not currently using `-fno-builtin-memset`. This is somewhat hidden by the fact that we use `-ffreestanding` globally and that `-ffreestanding` implies `-fno-builtin` for Clang. This patch also removes `-mllvm -combiner-global-alias-analysis` that is Clang specific and that does not bring substantial gains on modern processors. Also we keep `-mllvm --tail-merge-threshold=0` for aarch64 in CMakeLists.txt but we omit it in the Bazel config. This is because Bazel consumes the source files directly and so it can use PGO to take optimal decisions locally. Differential Revision: https://reviews.llvm.org/D126773
llvm · Jun 1, 2022 · b2a9ea4 · b2a9ea4
1 parent f951a6b
commit b2a9ea4
Show file tree

Hide file tree

Showing 4 changed files with 11 additions and 44 deletions.
diff --git a/libc/cmake/modules/LLVMLibCObjectRules.cmake b/libc/cmake/modules/LLVMLibCObjectRules.cmake
@@ -3,7 +3,7 @@ set(OBJECT_LIBRARY_TARGET_TYPE "OBJECT_LIBRARY")
 function(_get_common_compile_options output_var)
   set(compile_options ${LIBC_COMPILE_OPTIONS_DEFAULT} ${ARGN})
   if(NOT ${LIBC_TARGET_OS} STREQUAL "windows")
-    set(compile_options ${compile_options} -fpie -ffreestanding)
+    set(compile_options ${compile_options} -fpie -ffreestanding -fno-builtin)
   endif()
   if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
     list(APPEND compile_options "-fno-exceptions")

diff --git a/libc/src/string/CMakeLists.txt b/libc/src/string/CMakeLists.txt
@@ -279,7 +279,6 @@ function(add_implementation name impl_name)
     ${ARGN})
 
   if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
-    list(APPEND ADD_IMPL_MLLVM_COMPILE_OPTIONS "-combiner-global-alias-analysis")
     # Note that '-mllvm' needs to be prefixed with 'SHELL:' to prevent CMake flag deduplication.
     foreach(opt IN LISTS ADD_IMPL_MLLVM_COMPILE_OPTIONS)
       list(APPEND ADD_IMPL_COMPILE_OPTIONS "SHELL:-mllvm ${opt}")
@@ -309,9 +308,6 @@ function(add_bcmp bcmp_name)
     DEPENDS
       .memory_utils.memory_utils
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memcmp
-      -fno-builtin-bcmp
     ${ARGN}
   )
 endfunction()
@@ -339,8 +335,6 @@ function(add_bzero bzero_name)
     DEPENDS
       .memory_utils.memset_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-bzero
     ${ARGN}
   )
 endfunction()
@@ -368,8 +362,6 @@ function(add_memcmp memcmp_name)
     DEPENDS
       .memory_utils.memcmp_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memcmp
     ${ARGN}
   )
 endfunction()
@@ -400,8 +392,6 @@ function(add_memcpy memcpy_name)
     DEPENDS
       .memory_utils.memcpy_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memcpy
     ${ARGN}
   )
 endfunction()
@@ -434,8 +424,6 @@ function(add_memmove memmove_name)
     DEPENDS
       .memory_utils.memory_utils
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin
     ${ARGN}
   )
 endfunction()
@@ -468,8 +456,6 @@ function(add_memset memset_name)
     DEPENDS
       .memory_utils.memset_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memset
     ${ARGN}
   )
 endfunction()

diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -9,6 +9,7 @@ load("@bazel_skylib//lib:selects.bzl", "selects")
 
 package(
     default_visibility = ["//visibility:public"],
+    features = ["-header_modules"],
     licenses = ["notice"],
 )
 
@@ -85,15 +86,21 @@ cc_library(
     hdrs = [
         "src/__support/CPP/UInt.h",
     ],
-    deps = [":libc_root","__support_cpp_array"],
+    deps = [
+        "__support_cpp_array",
+        ":libc_root",
+    ],
 )
 
 cc_library(
     name = "__support_cpp_type_traits",
     hdrs = [
         "src/__support/CPP/TypeTraits.h",
     ],
-    deps = [":libc_root","__support_cpp_uint"],
+    deps = [
+        "__support_cpp_uint",
+        ":libc_root",
+    ],
 )
 
 cc_library(
@@ -806,12 +813,6 @@ libc_function(
     name = "memcpy",
     srcs = ["src/string/memcpy.cpp"],
     hdrs = ["src/string/memcpy.h"],
-    copts = [
-        "-fno-builtin-memcpy",
-        "-fno-builtin-memmove",
-        "-mllvm -combiner-global-alias-analysis",
-        "-mllvm --tail-merge-threshold=0",
-    ],
     features = no_sanitize_features,
     deps = [
         ":__support_common",
@@ -823,10 +824,6 @@ libc_function(
     name = "memset",
     srcs = ["src/string/memset.cpp"],
     hdrs = ["src/string/memset.h"],
-    copts = [
-        "-fno-builtin-memset",
-        "-mllvm -combiner-global-alias-analysis",
-    ],
     features = no_sanitize_features,
     deps = [
         ":__support_common",
@@ -838,10 +835,6 @@ libc_function(
     name = "memmove",
     srcs = ["src/string/memmove.cpp"],
     hdrs = ["src/string/memmove.h"],
-    copts = [
-        "-fno-builtin-memmove",
-        "-mllvm -combiner-global-alias-analysis",
-    ],
     features = no_sanitize_features,
     deps = [
         ":__support_common",
@@ -855,10 +848,6 @@ libc_function(
     name = "memcmp",
     srcs = ["src/string/memcmp.cpp"],
     hdrs = ["src/string/memcmp.h"],
-    copts = [
-        "-fno-builtin-memcmp",
-        "-mllvm -combiner-global-alias-analysis",
-    ],
     features = no_sanitize_features,
     deps = [
         ":__support_common",
@@ -871,10 +860,6 @@ libc_function(
     name = "bcmp",
     srcs = ["src/string/bcmp.cpp"],
     hdrs = ["src/string/bcmp.h"],
-    copts = [
-        "-fno-builtin-bcmp",
-        "-fno-builtin-memcmp",
-    ],
     features = no_sanitize_features,
     deps = [
         ":__support_common",
@@ -886,11 +871,6 @@ libc_function(
     name = "bzero",
     srcs = ["src/string/bzero.cpp"],
     hdrs = ["src/string/bzero.h"],
-    copts = [
-        "-fno-builtin-bzero",
-        "-fno-builtin-memset",
-        "-mllvm -combiner-global-alias-analysis",
-    ],
     features = no_sanitize_features,
     deps = [
         ":__support_common",

diff --git a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
@@ -31,6 +31,7 @@ def libc_function(name, srcs, deps = None, copts = None, **kwargs):
     deps.append(LIBC_ROOT_TARGET)
     copts = copts or []
     copts.append("-O3")
+    copts.append("-fno-builtin")
 
     # We compile the code twice, the first target is suffixed with ".__internal__" and contains the
     # C++ functions in the "__llvm_libc" namespace. This allows us to test the function in the