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

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/D125894

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 ${LLVM_CXX_STD_default} ${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")

libc/src/string/CMakeLists.txt

@@ -268,7 +268,6 @@ 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}")
@@ -298,9 +297,6 @@ function(add_bcmp bcmp_name)
     DEPENDS
       .memory_utils.memory_utils
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memcmp
-      -fno-builtin-bcmp
     ${ARGN}
   )
 endfunction()
@@ -328,8 +324,6 @@ function(add_bzero bzero_name)
     DEPENDS
       .memory_utils.memset_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-bzero
     ${ARGN}
   )
 endfunction()
@@ -357,8 +351,6 @@ function(add_memcmp memcmp_name)
     DEPENDS
       .memory_utils.memcmp_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memcmp
     ${ARGN}
   )
 endfunction()
@@ -389,8 +381,6 @@ function(add_memcpy memcpy_name)
     DEPENDS
       .memory_utils.memcpy_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memcpy
     ${ARGN}
   )
 endfunction()
@@ -423,8 +413,6 @@ function(add_memmove memmove_name)
     DEPENDS
       .memory_utils.memory_utils
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin
     ${ARGN}
   )
 endfunction()
@@ -457,8 +445,6 @@ function(add_memset memset_name)
     DEPENDS
       .memory_utils.memset_implementation
       libc.include.string
-    COMPILE_OPTIONS
-      -fno-builtin-memset
     ${ARGN}
   )
 endfunction()

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -85,7 +85,10 @@ cc_library(
     hdrs = [
         "src/__support/CPP/UInt.h",
     ],
-    deps = [":libc_root","__support_cpp_array"],
+    deps = [
+        "__support_cpp_array",
+        ":libc_root",
+    ],
 )
 
 cc_library(
@@ -93,7 +96,10 @@ cc_library(
     hdrs = [
         "src/__support/CPP/TypeTraits.h",
     ],
-    deps = [":libc_root","__support_cpp_uint"],
+    deps = [
+        "__support_cpp_uint",
+        ":libc_root",
+    ],
 )
 
 cc_library(
@@ -805,12 +811,6 @@ 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",
@@ -822,10 +822,6 @@ 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",
@@ -837,10 +833,6 @@ 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",
@@ -854,10 +846,6 @@ 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",
@@ -870,10 +858,6 @@ 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",
@@ -885,11 +869,6 @@ 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",

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