diff --git a/llvm-runtimes/compiler-rt/Manifest b/llvm-runtimes/compiler-rt/Manifest
index 96e15bdb78411..8bce92a2e98ef 100644
--- a/llvm-runtimes/compiler-rt/Manifest
+++ b/llvm-runtimes/compiler-rt/Manifest
@@ -13,5 +13,6 @@ DIST llvm-project-19.1.7.src.tar.xz 141249332 BLAKE2B 1259ed7f9aca7b35e89d818bef
 DIST llvm-project-19.1.7.src.tar.xz.sig 438 BLAKE2B 4015140f4ba77de45039bdbdfbaf6f30e75705123d067ea97175d91d7a5b6a75008df01d99ae7aa16aaa3b101f3f41e38d01f04158f95a261d617b3ede0254cd SHA512 195797b06ac80a742e0ccbc03a50dc06dd2e04377d783d5474e3e72c5a75203b60292b047929312a411d22b137a239943fba414a4d136a2be14cbff978eb6bda
 DIST llvm-project-20.1.5.src.tar.xz 147239812 BLAKE2B 992ebec16a11f32f234ba8b9f228f27939cdaeaaba474a08da2564ba3075bb10ab92a44be704666bdd77f8294321d43da40bb9245c411a86cd53cff88223a91f SHA512 3b7e657714fa9b943c75ec9eeb903018ab4713b1c3370746ba68893220729f178dabb971515741519f24e7ad0fa1dbce1345572bcf1d1fc1e5de97e4d2900a6b
 DIST llvm-project-20.1.5.src.tar.xz.sig 566 BLAKE2B c8be202b475726817893e1fe5fe2d3ab02ea1d3130ccfdf4c2c29b46e6aef79091de78e8a9aef59416ac1120bb3af6fdf47464db9b27b8fb4cb4194b0444e571 SHA512 c1bd30af5f7bfa6cac73994e9068d2791d9d27e86375fb15ad426422ad00cb43ade226c1b91ecc7daa950efae62c86300e4290d59649310f4e8fab5bdcb264fe
+DIST llvm-project-7dc7c155251c0008d5d59b84f0c9056365740f11.tar.gz 235921149 BLAKE2B 2867e313cd25fee6975da9bf65365fa51ed8780f3f8fc95983fb6e8f5b2c38c6d7f75a386b0ec2d74bafad74472973f4e4e603a5a0754465ac2b75942b8e90c6 SHA512 f8bc383ff2a1af836357150efa5728c7df3cd862f56ffaf12b5fc56ef631f1048276ff00b89fcf4d224576fa1eda9811d971886aae0855a4d29178060eb89a49
 DIST llvm-project-aaaae99663dbb220c6c27fa9cacf93fcb8f20e7c.tar.gz 235477577 BLAKE2B 46a3b7863cdfde75045dfcab95f8c9eee21f8ce80cee700284bc174adbb4038f23bba3b15635c88c2723ed0d20e6fddcf43c92b9e540c885af48e81bfa8c82aa SHA512 bf8e7f28622f91da57698220fca592105d109c38801b5e0312f5e290bca1ae32ef393179cfe912c194dbf85ece9bd6ee63b587157b0fcd6007bbaff3324e77ed
 DIST llvm-project-fcb4bda9dcfcdb64d8b069e8416c75d7a1a62e52.tar.gz 233149231 BLAKE2B 95a7a012a1e747afcf83ace3785c8ef6a3e10f6075e59eb1c5b077cc9edae244b648f341bc0ac6a45b2afc8f7ffe130a90a741a04465523f30f8322566386703 SHA512 b46f0c90a1c56750cada24183ca382b267a2d2faa0db7d77a8bdd4e94e6303e57d565cf85447b3c0e0efdd3750efef1e10e8ce6f1fe8f1ae10ee31d25ddf3fb7
diff --git a/llvm-runtimes/compiler-rt/compiler-rt-21.0.0_pre20250523.ebuild b/llvm-runtimes/compiler-rt/compiler-rt-21.0.0_pre20250523.ebuild
new file mode 100644
index 0000000000000..812a99f9d2a6d
--- /dev/null
+++ b/llvm-runtimes/compiler-rt/compiler-rt-21.0.0_pre20250523.ebuild
@@ -0,0 +1,175 @@
+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+PYTHON_COMPAT=( python3_{10..13} )
+inherit cmake crossdev flag-o-matic llvm.org llvm-utils python-any-r1
+inherit toolchain-funcs
+
+DESCRIPTION="Compiler runtime library for clang (built-in part)"
+HOMEPAGE="https://llvm.org/"
+
+LICENSE="Apache-2.0-with-LLVM-exceptions || ( UoI-NCSA MIT )"
+SLOT="${LLVM_MAJOR}"
+IUSE="+abi_x86_32 abi_x86_64 +atomic-builtins +clang +debug test"
+REQUIRED_USE="atomic-builtins? ( clang )"
+RESTRICT="!test? ( test ) !clang? ( test )"
+
+DEPEND="
+	llvm-core/llvm:${LLVM_MAJOR}
+"
+BDEPEND="
+	clang? ( llvm-core/clang:${LLVM_MAJOR} )
+	test? (
+		$(python_gen_any_dep ">=dev-python/lit-15[\${PYTHON_USEDEP}]")
+		=llvm-core/clang-${LLVM_VERSION}*:${LLVM_MAJOR}
+	)
+	!test? (
+		${PYTHON_DEPS}
+	)
+"
+
+LLVM_COMPONENTS=( compiler-rt cmake llvm/cmake )
+LLVM_TEST_COMPONENTS=( llvm/include/llvm/TargetParser )
+llvm.org_set_globals
+
+python_check_deps() {
+	use test || return 0
+	python_has_version ">=dev-python/lit-15[${PYTHON_USEDEP}]"
+}
+
+pkg_pretend() {
+	if ! use clang && ! tc-is-clang; then
+		ewarn "Building using a compiler other than clang may result in broken atomics"
+		ewarn "library. Enable USE=clang unless you have a very good reason not to."
+	fi
+}
+
+pkg_setup() {
+	if target_is_not_host || tc-is-cross-compiler ; then
+		# strips vars like CFLAGS="-march=x86_64-v3" for non-x86 architectures
+		CHOST=${CTARGET} strip-unsupported-flags
+		# overrides host docs otherwise
+		DOCS=()
+	fi
+	python-any-r1_pkg_setup
+}
+
+test_compiler() {
+	target_is_not_host && return
+	$(tc-getCC) ${CFLAGS} ${LDFLAGS} "${@}" -o /dev/null -x c - \
+		<<<'int main() { return 0; }' &>/dev/null
+}
+
+src_configure() {
+	llvm_prepend_path "${LLVM_MAJOR}"
+
+	# LLVM_ENABLE_ASSERTIONS=NO does not guarantee this for us, #614844
+	use debug || local -x CPPFLAGS="${CPPFLAGS} -DNDEBUG"
+
+	# pre-set since we need to pass it to cmake
+	BUILD_DIR=${WORKDIR}/${P}_build
+
+	if use clang && ! is_crosspkg; then
+		# Only do this conditionally to allow overriding with
+		# e.g. CC=clang-13 in case of breakage
+		if ! tc-is-clang ; then
+			local -x CC=${CHOST}-clang
+			local -x CXX=${CHOST}-clang++
+		fi
+
+		strip-unsupported-flags
+	fi
+
+	if ! is_crosspkg && ! test_compiler ; then
+		local nolib_flags=( -nodefaultlibs -lc )
+
+		if test_compiler "${nolib_flags[@]}"; then
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		elif test_compiler "${nolib_flags[@]}" -nostartfiles; then
+			# Avoiding -nostartfiles earlier on for bug #862540,
+			# and set available entry symbol for bug #862798.
+			nolib_flags+=( -nostartfiles -e main )
+
+			local -x LDFLAGS="${LDFLAGS} ${nolib_flags[*]}"
+			ewarn "${CC} seems to lack runtime, trying with ${nolib_flags[*]}"
+		fi
+	fi
+
+	local mycmakeargs=(
+		-DCOMPILER_RT_INSTALL_PATH="${EPREFIX}/usr/lib/clang/${LLVM_MAJOR}"
+
+		-DCOMPILER_RT_EXCLUDE_ATOMIC_BUILTIN=$(usex !atomic-builtins)
+		-DCOMPILER_RT_INCLUDE_TESTS=$(usex test)
+		-DCOMPILER_RT_BUILD_CTX_PROFILE=OFF
+		-DCOMPILER_RT_BUILD_LIBFUZZER=OFF
+		-DCOMPILER_RT_BUILD_MEMPROF=OFF
+		-DCOMPILER_RT_BUILD_ORC=OFF
+		-DCOMPILER_RT_BUILD_PROFILE=OFF
+		-DCOMPILER_RT_BUILD_SANITIZERS=OFF
+		-DCOMPILER_RT_BUILD_XRAY=OFF
+
+		-DPython3_EXECUTABLE="${PYTHON}"
+	)
+
+	if use amd64 && ! target_is_not_host; then
+		mycmakeargs+=(
+			-DCAN_TARGET_i386=$(usex abi_x86_32)
+			-DCAN_TARGET_x86_64=$(usex abi_x86_64)
+		)
+	fi
+
+	if is_crosspkg; then
+		# Needed to target built libc headers
+		export CFLAGS="${CFLAGS} -isystem /usr/${CTARGET}/usr/include"
+		mycmakeargs+=(
+			# Without this, the compiler will compile a test program
+			# and fail due to no builtins.
+			-DCMAKE_C_COMPILER_WORKS=1
+			-DCMAKE_CXX_COMPILER_WORKS=1
+
+			# Without this, compiler-rt install location is not unique
+			# to target triples, only to architecture.
+			# Needed if you want to target multiple libcs for one arch.
+			-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
+
+			-DCMAKE_ASM_COMPILER_TARGET="${CTARGET}"
+			-DCMAKE_C_COMPILER_TARGET="${CTARGET}"
+			-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
+		)
+	fi
+
+	if use prefix && [[ "${CHOST}" == *-darwin* ]] ; then
+		mycmakeargs+=(
+			# setting -isysroot is disabled with compiler-rt-prefix-paths.patch
+			# this allows adding arm64 support using SDK in EPREFIX
+			-DDARWIN_macosx_CACHED_SYSROOT="${EPREFIX}/MacOSX.sdk"
+			# Set version based on the SDK in EPREFIX.
+			# This disables i386 for SDK >= 10.15
+			-DDARWIN_macosx_OVERRIDE_SDK_VERSION="$(realpath "${EPREFIX}/MacOSX.sdk" | sed -e 's/.*MacOSX\(.*\)\.sdk/\1/')"
+			# Use our libtool instead of looking it up with xcrun
+			-DCMAKE_LIBTOOL="${EPREFIX}/usr/bin/${CHOST}-libtool"
+		)
+	fi
+
+	if use test; then
+		mycmakeargs+=(
+			-DLLVM_EXTERNAL_LIT="${EPREFIX}/usr/bin/lit"
+			-DLLVM_LIT_ARGS="$(get_lit_flags)"
+
+			-DCOMPILER_RT_TEST_COMPILER="${EPREFIX}/usr/lib/llvm/${LLVM_MAJOR}/bin/clang"
+			-DCOMPILER_RT_TEST_CXX_COMPILER="${EPREFIX}/usr/lib/llvm/${LLVM_MAJOR}/bin/clang++"
+		)
+	fi
+
+	cmake_src_configure
+}
+
+src_test() {
+	# respect TMPDIR!
+	local -x LIT_PRESERVES_TMP=1
+
+	cmake_build check-builtins
+}