build-script: Permit to build compiler-rt with LLVM_ENABLE_RUNTIMES

edymtt · edymtt · commit 3a7a4081be59 · 2025-03-20T12:49:42.000-07:00
LLVM-21 plans to remove the legacy method for building compiler-rt
in the same invocation as LLVM using `LLVM_ENABLED_PROJECTS` and
`LLVM_BUILD_EXTERNAL_COMPILER_RT`.

Support the new way of building compiler-rt with a new build-script
opt-in flag `--llvm-build-compiler-rt-with-use-runtimes` --
this will allow a staged introduction, and will ensure we can revert
back to the old behaviour temporarily in case of unforeseen regression.

Since this flag is meant to be short lived, in an attempt to keep the
logic simple we are gating on it only the
CMake cache entries that strictly control the compilation mode, all the
other entries used for configuring are added in both modes.

Take this chance to remove some stale code from `build-script-impl`, and
move some code in the generic CMake product to the LLVM one.

Addresses rdar://147505298
diff --git a/utils/build-script-impl b/utils/build-script-impl
@@ -803,20 +803,6 @@ function set_build_options_for_host() {
     esac
 
 
-    # We don't currently support building compiler-rt for cross-compile targets.
-    # It's not clear that's useful anyway.
-    if [[ $(is_cross_tools_host "${host}") ]] ; then
-      llvm_cmake_options+=(
-          -DLLVM_TOOL_COMPILER_RT_BUILD:BOOL=FALSE
-          -DLLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL=FALSE
-      )
-    else
-      llvm_cmake_options+=(
-          -DLLVM_TOOL_COMPILER_RT_BUILD:BOOL="$(false_true ${SKIP_BUILD_COMPILER_RT})"
-          -DLLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL="$(false_true ${SKIP_BUILD_COMPILER_RT})"
-      )
-    fi
-
     # If we are asked to not generate test targets for LLVM and or Swift,
     # disable as many LLVM tools as we can. This improves compile time when
     # compiling with LTO.
diff --git a/utils/build_swift/build_swift/defaults.py b/utils/build_swift/build_swift/defaults.py
@@ -122,6 +122,8 @@ def llvm_install_components():
     """Convenience function for getting the default llvm install components for
     platforms.
     """
+    # llvm build product will take care of replacing compiler-rt with
+    # builtins,runtimes if need be
     components = ['llvm-ar', 'llvm-cov', 'llvm-profdata', 'IndexStore', 'clang',
                   'clang-resource-headers', 'compiler-rt', 'clangd', 'LTO',
                   'lld']
diff --git a/utils/build_swift/build_swift/driver_arguments.py b/utils/build_swift/build_swift/driver_arguments.py
@@ -1398,6 +1398,11 @@ def create_argument_parser():
                 'separated options "-DCMAKE_VAR1=YES,-DCMAKE_VAR2=/tmp". Can '
                 'be called multiple times to add multiple such options.')
 
+    option('--llvm-build-compiler-rt-with-use-runtimes', toggle_true,
+           help='Switch to LLVM_USE_RUNTIMES as the mechanism to build compiler-rt'
+                'It will become the default with LLVM 21, this flag is '
+                'meant to stage its introduction and account for edge cases')
+
     # -------------------------------------------------------------------------
     in_group('Build settings for Android')
 
diff --git a/utils/build_swift/tests/expected_options.py b/utils/build_swift/tests/expected_options.py
@@ -232,6 +232,7 @@
     'lldb_build_variant': 'Debug',
     'lldb_build_with_xcode': '0',
     'llvm_assertions': True,
+    'llvm_build_compiler_rt_with_use_runtimes': False,
     'llvm_build_variant': 'Debug',
     'llvm_cmake_options': [],
     'llvm_enable_modules': False,
@@ -853,6 +854,7 @@ class BuildScriptImplOption(_BaseOption):
     AppendOption('--llvm-ninja-targets'),
     AppendOption('--llvm-ninja-targets-for-cross-compile-hosts'),
     AppendOption('--llvm-cmake-options'),
+    SetTrueOption('--llvm-build-compiler-rt-with-use-runtimes'),
     AppendOption('--darwin-symroot-path-filters'),
 
     UnsupportedOption('--build-jobs'),
diff --git a/utils/swift_build_support/swift_build_support/products/cmake_product.py b/utils/swift_build_support/swift_build_support/products/cmake_product.py
@@ -381,19 +381,6 @@ def host_cmake_options(self, host_target):
             # in the compiler checks CMake performs
             swift_cmake_options.define('CMAKE_OSX_ARCHITECTURES', arch)
 
-        # We don't currently support building compiler-rt for cross-compile targets.
-        # It's not clear that's useful anyway.
-        if self.is_cross_compile_target(host_target):
-            llvm_cmake_options.define('LLVM_TOOL_COMPILER_RT_BUILD:BOOL', 'FALSE')
-            llvm_cmake_options.define('LLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL', 'FALSE')
-        else:
-            llvm_cmake_options.define('LLVM_TOOL_COMPILER_RT_BUILD:BOOL',
-                                      cmake.CMakeOptions.true_false(
-                                          self.args.build_compiler_rt))
-            llvm_cmake_options.define('LLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL',
-                                      cmake.CMakeOptions.true_false(
-                                          self.args.build_compiler_rt))
-
         # If we are asked to not generate test targets for LLVM and or Swift,
         # disable as many LLVM tools as we can. This improves compile time when
         # compiling with LTO.
diff --git a/utils/swift_build_support/swift_build_support/products/llvm.py b/utils/swift_build_support/swift_build_support/products/llvm.py
@@ -217,6 +217,22 @@ def should_build(self, host_target):
         # LLVM will always be built in part
         return True
 
+    @classmethod
+    def compute_cmake_args_for_runtimes(cls, host_target):
+        # Swift expects the old layout for the runtime directory
+        args_for_runtime = '-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR:BOOL=OFF'
+
+        if host_target.startswith('linux'):
+            # This preserves the behaviour we had when using
+            # LLVM_BUILD_EXTERNAL COMPILER_RT --
+            # that is, having the linker not complaing if symbols used
+            # by TSan are undefined (namely the ones for Blocks Runtime)
+            # In the long term, we want to remove this and
+            # build Blocks Runtime before LLVM
+            args_for_runtime += ';-DSANITIZER_COMMON_LINK_FLAGS:STRING=-Wl,-z,undefs'
+
+        return args_for_runtime
+
     def build(self, host_target):
         """build() -> void
 
@@ -291,18 +307,54 @@ def build(self, host_target):
         llvm_cmake_options.define('LLVM_INCLUDE_DOCS:BOOL', 'TRUE')
         llvm_cmake_options.define('LLVM_ENABLE_LTO:STRING', self.args.lto_type)
         llvm_cmake_options.define('COMPILER_RT_INTERCEPT_LIBDISPATCH', 'ON')
+        llvm_cmake_options.define(
+            'RUNTIMES_CMAKE_ARGS',
+            LLVM.compute_cmake_args_for_runtimes(host_target))
+        if system() == "Darwin":
+            llvm_cmake_options.define('LLVM_BUILTIN_TARGETS', 'arm64-apple-darwin')
+            llvm_cmake_options.define('LLVM_RUNTIME_TARGETS', 'arm64-apple-darwin')
+            llvm_cmake_options.define('RUNTIMES_BUILD_ALLOW_DARWIN', 'ON')
 
         if self.args.build_embedded_stdlib and system() == "Darwin":
             # Ask for Mach-O cross-compilation builtins (for Embedded Swift)
             llvm_cmake_options.define(
                 'COMPILER_RT_FORCE_BUILD_BAREMETAL_MACHO_BUILTINS_ARCHS:STRING',
                 'armv6 armv6m armv7 armv7m armv7em')
+            # TODO we likely need a more generic mechanism to add flags
+            # meant for the builtins build system
+            llvm_cmake_options.define(
+                'BUILTIN_CMAKE_ARGS',
+                '-DCOMPILER_RT_FORCE_BUILD_BAREMETAL_MACHO_BUILTINS_ARCHS:'
+                'STRING=armv6 armv6m armv7 armv7m armv7em')
 
         llvm_enable_projects = ['clang']
+        llvm_enable_runtimes = []
 
         if self.args.build_compiler_rt and \
                 not self.is_cross_compile_target(host_target):
-            llvm_enable_projects.append('compiler-rt')
+            if self.args.llvm_build_compiler_rt_with_use_runtimes:
+                llvm_enable_runtimes.append('compiler-rt')
+                build_targets.append("runtimes")
+                # This accounts for previous incremental runs that may have set
+                # those in the LLVM CMakeCache.txt
+                llvm_cmake_options.undefine('LLVM_TOOL_COMPILER_RT_BUILD')
+                llvm_cmake_options.undefine('LLVM_BUILD_EXTERNAL_COMPILER_RT')
+            else:
+                # No need to unset anything,
+                # since we set LLVM_ENABLE_RUNTIMES explicitly
+                llvm_enable_projects.append('compiler-rt')
+                llvm_cmake_options.define(
+                    'LLVM_TOOL_COMPILER_RT_BUILD:BOOL', 'TRUE')
+                llvm_cmake_options.define(
+                    'LLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL', 'TRUE')
+        else:
+            if not self.args.llvm_build_compiler_rt_with_use_runtimes:
+                # No need to unset anything,
+                # since we set LLVM_ENABLE_RUNTIMES explicitly
+                llvm_cmake_options.define(
+                    'LLVM_TOOL_COMPILER_RT_BUILD:BOOL', 'FALSE')
+                llvm_cmake_options.define(
+                    'LLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL', 'FALSE')
 
         if self.args.build_clang_tools_extra:
             llvm_enable_projects.append('clang-tools-extra')
@@ -316,18 +368,15 @@ def build(self, host_target):
         if self.args.build_lld:
             llvm_enable_projects.append('lld')
 
+        if self.args.test:
+            # LLVMTestingSupport is not built at part of `all`
+            # and is required by some Swift tests
+            build_targets.append('LLVMTestingSupport')
+
         llvm_cmake_options.define('LLVM_ENABLE_PROJECTS',
                                   ';'.join(llvm_enable_projects))
-
-        # In the near future we are aiming to build compiler-rt with
-        # LLVM_ENABLE_RUNTIMES
-        # Until that happens, we need to unset this variable from
-        # LLVM CMakeCache.txt for two reasons
-        # * prevent PRs testing this variable to affect other runs landing
-        #   unrelated features
-        # * avoid fallouts should we land such change and then have to revert
-        #   it to account for unforeseen regressions
-        llvm_cmake_options.undefine('LLVM_ENABLE_RUNTIMES')
+        llvm_cmake_options.define('LLVM_ENABLE_RUNTIMES',
+                                  ';'.join(llvm_enable_runtimes))
 
         # NOTE: This is not a dead option! It is relied upon for certain
         # bots/build-configs!
@@ -491,9 +540,21 @@ def install(self, host_target):
            self.args.llvm_install_components != 'all':
             install_targets = []
             components = self.args.llvm_install_components.split(';')
+            if self.args.llvm_build_compiler_rt_with_use_runtimes and \
+               'compiler-rt' in components:
+                # This is a courtesy fallback to avoid breaking downstream presets
+                # we are not aware of
+                components.remove('compiler-rt')
+                components.append('builtins')
+                components.append('runtimes')
+                print('warning: replaced legacy LLVM component compiler-rt '
+                      'with builtins;runtimes -- consider updating your preset',
+                      flush=True)
+
             for component in components:
-                if self.is_cross_compile_target(host_target):
-                    if component == 'compiler-rt':
+                if self.is_cross_compile_target(host_target) \
+                   or not self.args.build_compiler_rt:
+                    if component in ['compiler-rt', 'builtins', 'runtimes']:
                         continue
                 install_targets.append('install-{}'.format(component))
 
diff --git a/validation-test/BuildSystem/llvm-build-compiler-rt-with-enable-external-compiler-rt.test b/validation-test/BuildSystem/llvm-build-compiler-rt-with-enable-external-compiler-rt.test
@@ -0,0 +1,25 @@
+# REQUIRES: standalone_build
+
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --cmake %cmake  2>&1 | %FileCheck --check-prefix=EXTERNAL-COMPILER-RT-CHECK %s
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --llvm-build-compiler-rt-with-use-runtimes=0 --cmake %cmake  2>&1 | %FileCheck --check-prefix=EXTERNAL-COMPILER-RT-CHECK %s
+
+# EXTERNAL-COMPILER-RT-CHECK: Building llvm
+# EXTERNAL-COMPILER-RT-CHECK-DAG: cmake -G Ninja
+# EXTERNAL-COMPILER-RT-CHECK-SAME: -DLLVM_TOOL_COMPILER_RT_BUILD:BOOL=TRUE
+# EXTERNAL-COMPILER-RT-CHECK-SAME: -DLLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL=TRUE
+# EXTERNAL-COMPILER-RT-CHECK-SAME: -DLLVM_ENABLE_PROJECTS{{[^ ]*}}={{[^ ]*}}compiler-rt
+# EXTERNAL-COMPILER-RT-CHECK-SAME: llvm
+
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --skip-build-compiler-rt --cmake %cmake  2>&1 | %FileCheck --check-prefix=DONT-BUILT-COMPILER-RT %s
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --llvm-build-compiler-rt-with-use-runtimes=0 --skip-build-compiler-rt --cmake %cmake  2>&1 | %FileCheck --check-prefix=DONT-BUILT-COMPILER-RT %s
+
+# DONT-BUILT-COMPILER-RT: Building llvm
+# DONT-BUILT-COMPILER-RT-DAG: cmake -G Ninja
+# DONT-BUILT-COMPILER-RT-SAME: -DLLVM_TOOL_COMPILER_RT_BUILD:BOOL=FALSE
+# DONT-BUILT-COMPILER-RT-SAME: -DLLVM_BUILD_EXTERNAL_COMPILER_RT:BOOL=FALSE
+# DONT-BUILT-COMPILER-RT-NOT: compiler-rt
+# DONT-BUILT-COMPILER-RT-SAME: llvm
diff --git a/validation-test/BuildSystem/llvm-build-compiler-rt-with-use-runtimes.test b/validation-test/BuildSystem/llvm-build-compiler-rt-with-use-runtimes.test
@@ -0,0 +1,26 @@
+# REQUIRES: standalone_build
+
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --llvm-build-compiler-rt-with-use-runtimes --cmake %cmake  2>&1 | %FileCheck --check-prefix=LLVM-USE-RUNTIMES %s
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --llvm-build-compiler-rt-with-use-runtimes=1 --cmake %cmake  2>&1 | %FileCheck --check-prefix=LLVM-USE-RUNTIMES %s
+
+# LLVM-USE-RUNTIMES: Building llvm
+# LLVM-USE-RUNTIMES-DAG: cmake -G Ninja
+# LLVM-USE-RUNTIMES-SAME: -ULLVM_TOOL_COMPILER_RT_BUILD
+# LLVM-USE-RUNTIMES-SAME: -ULLVM_BUILD_EXTERNAL_COMPILER_RT
+# LLVM-USE-RUNTIMES-SAME: -DLLVM_ENABLE_RUNTIMES{{[^ ]*}}={{[^ ]*}}compiler-rt
+# LLVM-USE-RUNTIMES-SAME: runtimes
+# LLVM-USE-RUNTIMES-SAME: llvm
+
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --llvm-build-compiler-rt-with-use-runtimes --skip-build-compiler-rt --cmake %cmake  2>&1 | %FileCheck --check-prefix=DONT-BUILT-COMPILER-RT %s
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --skip-build --llvm-build-compiler-rt-with-use-runtimes=1 --skip-build-compiler-rt --cmake %cmake  2>&1 | %FileCheck --check-prefix=DONT-BUILT-COMPILER-RT %s
+
+# DONT-BUILT-COMPILER-RT: Building llvm
+# DONT-BUILT-COMPILER-RT-DAG: cmake -G Ninja
+# DONT-BUILT-COMPILER-RT-NOT: LLVM_TOOL_COMPILER_RT_BUILD
+# DONT-BUILT-COMPILER-RT-NOT: LLVM_BUILD_EXTERNAL_COMPILER_RT
+# DONT-BUILT-COMPILER-RT-NOT: compiler-rt
+# DONT-BUILT-COMPILER-RT-SAME: llvm
