NixOS · Apr 1, 2021 · Apr 1, 2021
diff --git a/pkgs/development/compilers/llvm/12/bintools.nix b/pkgs/development/compilers/llvm/12/bintools.nix
@@ -0,0 +1,29 @@
+{ runCommand, stdenv, llvm, lld, version }:
+
+let
+  prefix =
+    if stdenv.hostPlatform != stdenv.targetPlatform
+    then "${stdenv.targetPlatform.config}-"
+    else "";
+in runCommand "llvm-binutils-${version}" { preferLocalBuild = true; } ''
+   mkdir -p $out/bin
+   for prog in ${lld}/bin/*; do
+     ln -s $prog $out/bin/${prefix}$(basename $prog)
+   done
+   for prog in ${llvm}/bin/*; do
+     ln -sf $prog $out/bin/${prefix}$(basename $prog)
+   done
+
+   ln -s ${llvm}/bin/llvm-ar $out/bin/${prefix}ar
+   ln -s ${llvm}/bin/llvm-as $out/bin/${prefix}as
+   ln -s ${llvm}/bin/llvm-dwp $out/bin/${prefix}dwp
+   ln -s ${llvm}/bin/llvm-nm $out/bin/${prefix}nm
+   ln -s ${llvm}/bin/llvm-objcopy $out/bin/${prefix}objcopy
+   ln -s ${llvm}/bin/llvm-objdump $out/bin/${prefix}objdump
+   ln -s ${llvm}/bin/llvm-ranlib $out/bin/${prefix}ranlib
+   ln -s ${llvm}/bin/llvm-readelf $out/bin/${prefix}readelf
+   ln -s ${llvm}/bin/llvm-size $out/bin/${prefix}size
+   ln -s ${llvm}/bin/llvm-strip $out/bin/${prefix}strip
+
+   ln -s ${lld}/bin/lld $out/bin/${prefix}ld
+''
diff --git a/pkgs/development/compilers/llvm/12/clang/default.nix b/pkgs/development/compilers/llvm/12/clang/default.nix
@@ -0,0 +1,110 @@
+{ lib, stdenv, fetch, cmake, libxml2, llvm, version, clang-tools-extra_src, python3, lld
+, fixDarwinDylibNames
+, enableManpages ? false
+}:
+
+let
+  self = stdenv.mkDerivation ({
+    pname = "clang";
+    inherit version;
+
+    src = fetch "clang" "1xg2wy86zdj1d4h33n9mmb4j0x8bp9a5pk4qnnx3imlh8n6vhrqj";
+    inherit clang-tools-extra_src;
+
+    unpackPhase = ''
+      unpackFile $src
+      mv clang-* clang
+      sourceRoot=$PWD/clang
+      unpackFile ${clang-tools-extra_src}
+    '';
+
+    nativeBuildInputs = [ cmake python3 lld ]
+      ++ lib.optional enableManpages python3.pkgs.sphinx
+      ++ lib.optional stdenv.hostPlatform.isDarwin fixDarwinDylibNames;
+
+    buildInputs = [ libxml2 llvm ];
+
+    cmakeFlags = [
+      "-DCMAKE_CXX_FLAGS=-std=c++14"
+      "-DCLANGD_BUILD_XPC=OFF"
+    ] ++ lib.optionals enableManpages [
+      "-DCLANG_INCLUDE_DOCS=ON"
+      "-DLLVM_ENABLE_SPHINX=ON"
+      "-DSPHINX_OUTPUT_MAN=ON"
+      "-DSPHINX_OUTPUT_HTML=OFF"
+      "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
+    ];
+
+    patches = [
+      ./purity.patch
+      # https://reviews.llvm.org/D51899
+    ];
+
+    postPatch = ''
+      sed -i -e 's/DriverArgs.hasArg(options::OPT_nostdlibinc)/true/' \
+             -e 's/Args.hasArg(options::OPT_nostdlibinc)/true/' \
+             lib/Driver/ToolChains/*.cpp
+
+      # Patch for standalone doc building
+      sed -i '1s,^,find_package(Sphinx REQUIRED)\n,' docs/CMakeLists.txt
+    '' + lib.optionalString stdenv.hostPlatform.isMusl ''
+      sed -i -e 's/lgcc_s/lgcc_eh/' lib/Driver/ToolChains/*.cpp
+    '';
+
+    outputs = [ "out" "lib" "python" ];
+
+    # Clang expects to find LLVMgold in its own prefix
+    postInstall = ''
+      if [ -e ${llvm}/lib/LLVMgold.so ]; then
+        ln -sv ${llvm}/lib/LLVMgold.so $out/lib
+      fi
+
+      ln -sv $out/bin/clang $out/bin/cpp
+
+      # Move libclang to 'lib' output
+      moveToOutput "lib/libclang.*" "$lib"
+      moveToOutput "lib/libclang-cpp.*" "$lib"
+      substituteInPlace $out/lib/cmake/clang/ClangTargets-release.cmake \
+          --replace "\''${_IMPORT_PREFIX}/lib/libclang." "$lib/lib/libclang." \
+          --replace "\''${_IMPORT_PREFIX}/lib/libclang-cpp." "$lib/lib/libclang-cpp."
+
+      mkdir -p $python/bin $python/share/clang/
+      mv $out/bin/{git-clang-format,scan-view} $python/bin
+      if [ -e $out/bin/set-xcode-analyzer ]; then
+        mv $out/bin/set-xcode-analyzer $python/bin
+      fi
+      mv $out/share/clang/*.py $python/share/clang
+      rm $out/bin/c-index-test
+    '';
+
+    passthru = {
+      isClang = true;
+      inherit llvm;
+    };
+
+    meta = {
+      description = "A c, c++, objective-c, and objective-c++ frontend for the llvm compiler";
+      homepage    = "https://llvm.org/";
+      license     = lib.licenses.ncsa;
+      platforms   = lib.platforms.all;
+    };
+  } // lib.optionalAttrs enableManpages {
+    pname = "clang-manpages";
+
+    buildPhase = ''
+      make docs-clang-man
+    '';
+
+    installPhase = ''
+      mkdir -p $out/share/man/man1
+      # Manually install clang manpage
+      cp docs/man/*.1 $out/share/man/man1/
+    '';
+
+    outputs = [ "out" ];
+
+    doCheck = false;
+
+    meta.description = "man page for Clang ${version}";
+  });
+in self
diff --git a/pkgs/development/compilers/llvm/12/clang/purity.patch b/pkgs/development/compilers/llvm/12/clang/purity.patch
@@ -0,0 +1,28 @@
+From 4add81bba40dcec62c4ea4481be8e35ac53e89d8 Mon Sep 17 00:00:00 2001
+From: Will Dietz <w@wdtz.org>
+Date: Thu, 18 May 2017 11:56:12 -0500
+Subject: [PATCH] "purity" patch for 5.0
+
+---
+ lib/Driver/ToolChains/Gnu.cpp | 7 -------
+ 1 file changed, 7 deletions(-)
+
+diff --git a/lib/Driver/ToolChains/Gnu.cpp b/lib/Driver/ToolChains/Gnu.cpp
+index fe3c0191bb..c6a482bece 100644
+--- a/lib/Driver/ToolChains/Gnu.cpp
++++ b/lib/Driver/ToolChains/Gnu.cpp
+@@ -487,12 +487,6 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+   if (!IsStatic) {
+     if (Args.hasArg(options::OPT_rdynamic))
+       CmdArgs.push_back("-export-dynamic");
+-
+-    if (!Args.hasArg(options::OPT_shared) && !IsStaticPIE) {
+-      CmdArgs.push_back("-dynamic-linker");
+-      CmdArgs.push_back(Args.MakeArgString(Twine(D.DyldPrefix) +
+-                                           ToolChain.getDynamicLinker(Args)));
+-    }
+   }
+
+   CmdArgs.push_back("-o");
+-- 
+2.11.0
diff --git a/pkgs/development/compilers/llvm/12/compiler-rt-X86-support-extension.patch b/pkgs/development/compilers/llvm/12/compiler-rt-X86-support-extension.patch
@@ -0,0 +1,23 @@
+diff --git a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
+index 3a66dd9c3fb..7efc85d9f9f 100644
+--- a/lib/builtins/CMakeLists.txt
++++ b/lib/builtins/CMakeLists.txt
+@@ -301,6 +301,10 @@ if (NOT MSVC)
+     i386/umoddi3.S
+   )
+
++  set(i486_SOURCES ${i386_SOURCES})
++  set(i586_SOURCES ${i386_SOURCES})
++  set(i686_SOURCES ${i386_SOURCES})
++
+   if (WIN32)
+     set(i386_SOURCES
+       ${i386_SOURCES}
+@@ -608,6 +612,7 @@ else ()
+   endif()
+
+   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
++      message("arch: ${arch}")
+     if (CAN_TARGET_${arch})
+       # For ARM archs, exclude any VFP builtins if VFP is not supported
+       if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em)$")
diff --git a/pkgs/development/compilers/llvm/12/compiler-rt-armv7l.patch b/pkgs/development/compilers/llvm/12/compiler-rt-armv7l.patch
@@ -0,0 +1,32 @@
+diff -ur compiler-rt-10.0.0.src/cmake/builtin-config-ix.cmake compiler-rt-10.0.0.src-patched/cmake/builtin-config-ix.cmake
+--- compiler-rt-10.0.0.src/cmake/builtin-config-ix.cmake	2020-03-24 00:01:02.000000000 +0900
++++ compiler-rt-10.0.0.src-patched/cmake/builtin-config-ix.cmake	2020-05-10 03:42:00.883450706 +0900
+@@ -24,7 +24,7 @@
+
+
+ set(ARM64 aarch64)
+-set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k)
++set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k armv7l)
+ set(HEXAGON hexagon)
+ set(X86 i386)
+ set(X86_64 x86_64)
+diff -ur compiler-rt-10.0.0.src/lib/builtins/CMakeLists.txt compiler-rt-10.0.0.src-patched/lib/builtins/CMakeLists.txt
+--- compiler-rt-10.0.0.src/lib/builtins/CMakeLists.txt	2020-03-24 00:01:02.000000000 +0900
++++ compiler-rt-10.0.0.src-patched/lib/builtins/CMakeLists.txt	2020-05-10 03:44:49.468579650 +0900
+@@ -474,6 +474,7 @@
+ set(armv7_SOURCES ${arm_SOURCES})
+ set(armv7s_SOURCES ${arm_SOURCES})
+ set(armv7k_SOURCES ${arm_SOURCES})
++set(armv7l_SOURCES ${arm_SOURCES})
+ set(arm64_SOURCES ${aarch64_SOURCES})
+
+ # macho_embedded archs
+@@ -595,7 +596,7 @@
+   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
+     if (CAN_TARGET_${arch})
+       # For ARM archs, exclude any VFP builtins if VFP is not supported
+-      if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em)$")
++      if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7l|armv7m|armv7em)$")
+         string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}")
+         check_compile_definition(__VFP_FP__ "${CMAKE_C_FLAGS} ${_TARGET_${arch}_CFLAGS}" COMPILER_RT_HAS_${arch}_VFP)
+         if(NOT COMPILER_RT_HAS_${arch}_VFP)
diff --git a/pkgs/development/compilers/llvm/12/compiler-rt-codesign.patch b/pkgs/development/compilers/llvm/12/compiler-rt-codesign.patch
@@ -0,0 +1,33 @@
+From 3dec5f3475a26aeb4678627795c4b67c6b7b4785 Mon Sep 17 00:00:00 2001
+From: Will Dietz <w@wdtz.org>
+Date: Tue, 19 Sep 2017 13:13:06 -0500
+Subject: [PATCH] remove codesign use on Apple, disable ios sim testing that
+ needs it
+
+---
+ cmake/Modules/AddCompilerRT.cmake |  8 ------
+ test/asan/CMakeLists.txt          | 52 ---------------------------------------
+ test/tsan/CMakeLists.txt          | 47 -----------------------------------
+ 3 files changed, 107 deletions(-)
+
+diff --git a/cmake/Modules/AddCompilerRT.cmake b/cmake/Modules/AddCompilerRT.cmake
+index bc5fb9ff7..b64eb4246 100644
+--- a/cmake/Modules/AddCompilerRT.cmake
++++ b/cmake/Modules/AddCompilerRT.cmake
+@@ -210,14 +210,6 @@ function(add_compiler_rt_runtime name type)
+         set_target_properties(${libname} PROPERTIES IMPORT_PREFIX "")
+         set_target_properties(${libname} PROPERTIES IMPORT_SUFFIX ".lib")
+       endif()
+-      if(APPLE)
+-        # Ad-hoc sign the dylibs
+-        add_custom_command(TARGET ${libname}
+-          POST_BUILD  
+-          COMMAND codesign --sign - $<TARGET_FILE:${libname}>
+-          WORKING_DIRECTORY ${COMPILER_RT_LIBRARY_OUTPUT_DIR}
+-        )
+-      endif()
+     endif()
+     install(TARGETS ${libname}
+       ARCHIVE DESTINATION ${COMPILER_RT_LIBRARY_INSTALL_DIR}
+2.14.1
+
diff --git a/pkgs/development/compilers/llvm/12/compiler-rt.nix b/pkgs/development/compilers/llvm/12/compiler-rt.nix
@@ -0,0 +1,90 @@
+{ lib, stdenv, version, fetch, cmake, python3, llvm, libcxxabi }:
+
+let
+
+  useLLVM = stdenv.hostPlatform.useLLVM or false;
+  bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  inherit (stdenv.hostPlatform) isMusl;
+
+in
+
+stdenv.mkDerivation rec {
+  pname = "compiler-rt";
+  inherit version;
+  src = fetch pname "1n4jf0clwj3q0vfc7xjl0k4dqj69fvgsmib8qdqh45imgamnypvb";
+
+  nativeBuildInputs = [ cmake python3 llvm ];
+  buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
+
+  NIX_CFLAGS_COMPILE = [
+    "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0"
+  ];
+
+  cmakeFlags = [
+    "-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON"
+    "-DCMAKE_C_COMPILER_TARGET=${stdenv.hostPlatform.config}"
+    "-DCMAKE_ASM_COMPILER_TARGET=${stdenv.hostPlatform.config}"
+  ] ++ lib.optionals (stdenv.isDarwin) [
+    "-DDARWIN_macosx_OVERRIDE_SDK_VERSION=ON"
+    "-DDARWIN_osx_ARCHS=${stdenv.hostPlatform.parsed.cpu.name}"
+  ] ++ lib.optionals (useLLVM || bareMetal || isMusl) [
+    "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
+    "-DCOMPILER_RT_BUILD_XRAY=OFF"
+    "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
+    "-DCOMPILER_RT_BUILD_PROFILE=OFF"
+  ] ++ lib.optionals (useLLVM || bareMetal) [
+    "-DCMAKE_C_COMPILER_WORKS=ON"
+    "-DCMAKE_CXX_COMPILER_WORKS=ON"
+    "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM) [
+    "-DCOMPILER_RT_BUILD_BUILTINS=ON"
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
+    #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
+    "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
+  ] ++ lib.optionals (bareMetal) [
+    "-DCOMPILER_RT_OS_DIR=baremetal"
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  patches = [
+    ./compiler-rt-codesign.patch # Revert compiler-rt commit that makes codesign mandatory
+    ./compiler-rt-X86-support-extension.patch # Add support for i486 i586 i686 by reusing i386 config
+  ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
+    ++ lib.optional stdenv.hostPlatform.isAarch32 ./compiler-rt-armv7l.patch;
+
+
+  # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
+  # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
+  # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
+  # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
+  # a flag and turn the flag off during the stdenv build.
+  postPatch = lib.optionalString (!stdenv.isDarwin) ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + lib.optionalString stdenv.isDarwin ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(ARM64 arm64 arm64e)' 'set(ARM64)'
+    substituteInPlace cmake/config-ix.cmake \
+      --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
+  '' + lib.optionalString (useLLVM) ''
+    substituteInPlace lib/builtins/int_util.c \
+      --replace "#include <stdlib.h>" ""
+    substituteInPlace lib/builtins/clear_cache.c \
+      --replace "#include <assert.h>" ""
+    substituteInPlace lib/builtins/cpu_model.c \
+      --replace "#include <assert.h>" ""
+  '';
+
+  # Hack around weird upsream RPATH bug
+  postInstall = lib.optionalString (stdenv.hostPlatform.isDarwin || stdenv.hostPlatform.isWasm) ''
+    ln -s "$out/lib"/*/* "$out/lib"
+  '' + lib.optionalString (useLLVM) ''
+    ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
+    ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
+    ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
+    ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
+  '';
+
+}
diff --git a/pkgs/development/compilers/llvm/12/default.nix b/pkgs/development/compilers/llvm/12/default.nix
@@ -0,0 +1,204 @@
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+, libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
+, buildPackages
+, buildLlvmTools # tools, but from the previous stage, for cross
+, targetLlvmLibraries # libraries, but from the next stage, for cross
+, darwin
+}:
+
+let
+  release_version = "12.0.0";
+  candidate = "rc3"; # empty or "rcN"
+  dash-candidate = lib.optionalString (candidate != "") "-${candidate}";
+  version = "${release_version}${dash-candidate}"; # differentiating these (variables) is important for RCs
+  targetConfig = stdenv.targetPlatform.config;
+
+  fetch = name: sha256: fetchurl {
+    url = "https://github.com/llvm/llvm-project/releases/download/llvmorg-${version}/${name}-${release_version}${candidate}.src.tar.xz";
+    inherit sha256;
+  };
+
+  clang-tools-extra_src = fetch "clang-tools-extra" "1p6ln69iciwwpng226mfvxf3vylfvbz73y0a4y4v2rg7pn7hk671";
+
+  tools = lib.makeExtensible (tools: let
+    callPackage = newScope (tools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
+    mkExtraBuildCommands = cc: ''
+      rsrc="$out/resource-root"
+      mkdir "$rsrc"
+      ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
+      ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
+      ln -s "${targetLlvmLibraries.compiler-rt.out}/share" "$rsrc/share"
+      echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
+    '';
+  in {
+
+    llvm = callPackage ./llvm.nix { };
+
+    clang-unwrapped = callPackage ./clang {
+      inherit (tools) lld;
+      inherit clang-tools-extra_src;
+    };
+
+    # disabled until recommonmark supports sphinx 3
+    #Llvm-manpages = lowPrio (tools.llvm.override {
+    #  enableManpages = true;
+    #  python3 = pkgs.python3;  # don't use python-boot
+    #});
+
+    clang-manpages = lowPrio (tools.clang-unwrapped.override {
+      enableManpages = true;
+      python3 = pkgs.python3;  # don't use python-boot
+    });
+
+    # disabled until recommonmark supports sphinx 3
+    # lldb-manpages = lowPrio (tools.lldb.override {
+    #   enableManpages = true;
+    #   python3 = pkgs.python3;  # don't use python-boot
+    # });
+
+    libclang = tools.clang-unwrapped.lib;
+
+    clang = if stdenv.cc.isGNU then tools.libstdcxxClang else tools.libcxxClang;
+
+    libstdcxxClang = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      # libstdcxx is taken from gcc in an ad-hoc way in cc-wrapper.
+      libcxx = null;
+      extraPackages = [
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = mkExtraBuildCommands cc;
+    };
+
+    libcxxClang = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = targetLlvmLibraries.libcxx;
+      extraPackages = [
+        targetLlvmLibraries.libcxxabi
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = mkExtraBuildCommands cc;
+    };
+
+    lld = callPackage ./lld.nix {
+      libunwind = libraries.libunwind;
+    };
+
+    lldb = callPackage ./lldb.nix {
+      inherit (darwin) libobjc bootstrap_cmds;
+      inherit (darwin.apple_sdk.libs) xpc;
+      inherit (darwin.apple_sdk.frameworks) Foundation Carbon Cocoa;
+    };
+
+    # Below, is the LLVM bootstrapping logic. It handles building a
+    # fully LLVM toolchain from scratch. No GCC toolchain should be
+    # pulled in. As a consequence, it is very quick to build different
+    # targets provided by LLVM and we can also build for what GCC
+    # doesn’t support like LLVM. Probably we should move to some other
+    # file.
+
+    bintools = callPackage ./bintools.nix {};
+
+    lldClang = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = targetLlvmLibraries.libcxx;
+      bintools = wrapBintoolsWith {
+        inherit (tools) bintools;
+      };
+      extraPackages = [
+        targetLlvmLibraries.libcxxabi
+        targetLlvmLibraries.compiler-rt
+      ] ++ lib.optionals (!stdenv.targetPlatform.isWasm) [
+        targetLlvmLibraries.libunwind
+      ];
+      extraBuildCommands = ''
+        echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
+        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
+        echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString stdenv.targetPlatform.isWasm ''
+        echo "-fno-exceptions" >> $out/nix-support/cc-cflags
+      '' + mkExtraBuildCommands cc;
+    };
+
+    lldClangNoLibcxx = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      bintools = wrapBintoolsWith {
+        inherit (tools) bintools;
+      };
+      extraPackages = [
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = ''
+        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
+        echo "-nostdlib++" >> $out/nix-support/cc-cflags
+      '' + mkExtraBuildCommands cc;
+    };
+
+    lldClangNoLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      bintools = wrapBintoolsWith {
+        inherit (tools) bintools;
+        libc = null;
+      };
+      extraPackages = [
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = ''
+        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
+      '' + mkExtraBuildCommands cc;
+    };
+
+    lldClangNoCompilerRt = wrapCCWith {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      bintools = wrapBintoolsWith {
+        inherit (tools) bintools;
+        libc = null;
+      };
+      extraPackages = [ ];
+      extraBuildCommands = ''
+        echo "-nostartfiles" >> $out/nix-support/cc-cflags
+      '';
+    };
+
+  });
+
+  libraries = lib.makeExtensible (libraries: let
+    callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
+  in {
+
+    compiler-rt = callPackage ./compiler-rt.nix ({} //
+      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
+      }));
+
+    stdenv = overrideCC stdenv buildLlvmTools.clang;
+
+    libcxxStdenv = overrideCC stdenv buildLlvmTools.libcxxClang;
+
+    libcxx = callPackage ./libc++ ({} //
+      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+      }));
+
+    libcxxabi = callPackage ./libc++abi.nix ({} //
+      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+        libunwind = libraries.libunwind;
+      }));
+
+    openmp = callPackage ./openmp.nix {};
+
+    libunwind = callPackage ./libunwind.nix ({} //
+      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+      }));
+
+  });
+
+in { inherit tools libraries; } // libraries // tools
diff --git a/pkgs/development/compilers/llvm/12/libc++/default.nix b/pkgs/development/compilers/llvm/12/libc++/default.nix
@@ -0,0 +1,56 @@
+{ lib, stdenv, fetch, fetchpatch, cmake, python3, libcxxabi, llvm, fixDarwinDylibNames, version
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
+
+stdenv.mkDerivation {
+  pname = "libc++";
+  inherit version;
+
+  src = fetch "libcxx" "1114yvbipwdk1qk1xrb7s05hf7cycyknpf4ph0wbqpjzzzxk0hgk";
+
+  postUnpack = ''
+    unpackFile ${libcxxabi.src}
+    mv libcxxabi-* libcxxabi
+    unpackFile ${llvm.src}
+    mv llvm-* llvm
+  '';
+
+  patches = [
+    (fetchpatch {
+      # Backported from LLVM 12, avoids clashes with commonly used "block.h" header.
+      url = "https://github.com/llvm/llvm-project/commit/19bc9ea480b60b607a3e303f20c7a3a2ea553369.patch";
+      sha256 = "sha256-aWa66ogmPkG0xHzSfcpD0qZyZQcNKwLV44js4eiun78=";
+      stripLen = 1;
+    })
+  ] ++ lib.optional stdenv.hostPlatform.isMusl ../../libcxx-0001-musl-hacks.patch;
+
+  preConfigure = lib.optionalString stdenv.hostPlatform.isMusl ''
+    patchShebangs utils/cat_files.py
+  '';
+
+  nativeBuildInputs = [ cmake python3 ]
+    ++ lib.optional stdenv.isDarwin fixDarwinDylibNames;
+
+  buildInputs = [ libcxxabi ];
+
+  cmakeFlags = [
+    "-DLIBCXX_CXX_ABI=libcxxabi"
+  ] ++ lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) "-DLIBCXX_HAS_MUSL_LIBC=1"
+    ++ lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON"
+    ++ lib.optional stdenv.hostPlatform.isWasm [
+      "-DLIBCXX_ENABLE_THREADS=OFF"
+      "-DLIBCXX_ENABLE_FILESYSTEM=OFF"
+      "-DLIBCXX_ENABLE_EXCEPTIONS=OFF"
+    ] ++ lib.optional (!enableShared) "-DLIBCXX_ENABLE_SHARED=OFF";
+
+  passthru = {
+    isLLVM = true;
+  };
+
+  meta = {
+    homepage = "https://libcxx.llvm.org/";
+    description = "A new implementation of the C++ standard library, targeting C++11";
+    license = with lib.licenses; [ ncsa mit ];
+    platforms = lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/12/libc++abi.nix b/pkgs/development/compilers/llvm/12/libc++abi.nix
@@ -0,0 +1,69 @@
+{ lib, stdenv, cmake, fetch, libcxx, libunwind, llvm, version
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
+
+stdenv.mkDerivation {
+  pname = "libc++abi";
+  inherit version;
+
+  src = fetch "libcxxabi" "1vdc6zld5rlbrbpxf0fxs0m6k1cabpi82ksiwgj1pmhx8l140n0q";
+
+  nativeBuildInputs = [ cmake ];
+  buildInputs = lib.optional (!stdenv.isDarwin && !stdenv.isFreeBSD && !stdenv.hostPlatform.isWasm) libunwind;
+
+  cmakeFlags = lib.optionals (stdenv.hostPlatform.useLLVM or false) [
+    "-DLLVM_ENABLE_LIBCXX=ON"
+    "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
+  ] ++ lib.optionals stdenv.hostPlatform.isWasm [
+    "-DLIBCXXABI_ENABLE_THREADS=OFF"
+    "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF"
+  ] ++ lib.optionals (!enableShared) [
+    "-DLIBCXXABI_ENABLE_SHARED=OFF"
+  ];
+
+  patches = [ ./libcxxabi-no-threads.patch ];
+
+  postUnpack = ''
+    unpackFile ${libcxx.src}
+    mv libcxx-* libcxx
+    unpackFile ${llvm.src}
+    mv llvm-* llvm
+  '' + lib.optionalString stdenv.isDarwin ''
+    export TRIPLE=x86_64-apple-darwin
+  '' + lib.optionalString stdenv.hostPlatform.isMusl ''
+    patch -p1 -d libcxx -i ${../libcxx-0001-musl-hacks.patch}
+  '' + lib.optionalString stdenv.hostPlatform.isWasm ''
+    patch -p1 -d llvm -i ${./libcxxabi-wasm.patch}
+  '';
+
+  installPhase = if stdenv.isDarwin
+    then ''
+      for file in lib/*.dylib; do
+        # this should be done in CMake, but having trouble figuring out
+        # the magic combination of necessary CMake variables
+        # if you fancy a try, take a look at
+        # https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/RPATH-handling
+        install_name_tool -id $out/$file $file
+      done
+      make install
+      install -d 755 $out/include
+      install -m 644 ../include/*.h $out/include
+    ''
+    else ''
+      install -d -m 755 $out/include $out/lib
+      install -m 644 lib/libc++abi.a $out/lib
+      install -m 644 ../include/cxxabi.h $out/include
+    '' + lib.optionalString enableShared ''
+      install -m 644 lib/libc++abi.so.1.0 $out/lib
+      ln -s libc++abi.so.1.0 $out/lib/libc++abi.so
+      ln -s libc++abi.so.1.0 $out/lib/libc++abi.so.1
+    '';
+
+  meta = {
+    homepage = "https://libcxxabi.llvm.org/";
+    description = "A new implementation of low level support for a standard C++ library";
+    license = with lib.licenses; [ ncsa mit ];
+    maintainers = with lib.maintainers; [ vlstill ];
+    platforms = lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/12/libcxxabi-no-threads.patch b/pkgs/development/compilers/llvm/12/libcxxabi-no-threads.patch
@@ -0,0 +1,12 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 4138acf..41b4763 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -362,6 +362,7 @@ if (NOT LIBCXXABI_ENABLE_THREADS)
+                         " is also set to ON.")
+   endif()
+   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
++  add_definitions(-D_LIBCPP_HAS_NO_THREADS)
+ endif()
+
+ if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)
diff --git a/pkgs/development/compilers/llvm/12/libcxxabi-wasm.patch b/pkgs/development/compilers/llvm/12/libcxxabi-wasm.patch
@@ -0,0 +1,16 @@
+diff --git a/cmake/modules/HandleLLVMOptions.cmake b/cmake/modules/HandleLLVMOptions.cmake
+index 15497d405e0..33f7f18193a 100644
+--- a/cmake/modules/HandleLLVMOptions.cmake
++++ b/cmake/modules/HandleLLVMOptions.cmake
+@@ -127,7 +127,10 @@ else(WIN32)
+       set(LLVM_HAVE_LINK_VERSION_SCRIPT 1)
+     endif()
+   else(FUCHSIA OR UNIX)
+-    MESSAGE(SEND_ERROR "Unable to determine platform")
++    if(${CMAKE_SYSTEM_NAME} MATCHES "Wasi")
++    else()
++      MESSAGE(SEND_ERROR "Unable to determine platform")
++    endif()
+   endif(FUCHSIA OR UNIX)
+ endif(WIN32)
+
diff --git a/pkgs/development/compilers/llvm/12/libunwind.nix b/pkgs/development/compilers/llvm/12/libunwind.nix
@@ -0,0 +1,14 @@
+{ lib, stdenv, version, fetch, cmake, fetchpatch
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
+
+stdenv.mkDerivation rec {
+  pname = "libunwind";
+  inherit version;
+
+  src = fetch pname "18n3k2kf6pyvzspnz1i22czbgi14kmch76fxml8kvhky7mw7v1yz";
+
+  nativeBuildInputs = [ cmake ];
+
+  cmakeFlags = lib.optional (!enableShared) "-DLIBUNWIND_ENABLE_SHARED=OFF";
+}
diff --git a/pkgs/development/compilers/llvm/12/lld.nix b/pkgs/development/compilers/llvm/12/lld.nix
@@ -0,0 +1,39 @@
+{ lib, stdenv
+, fetch
+, libunwind
+, cmake
+, libxml2
+, llvm
+, version
+}:
+
+stdenv.mkDerivation rec {
+  pname = "lld";
+  inherit version;
+
+  src = fetch pname "097pxd7hgipr538vi48q8fi5svbd03bx3d078a06wigmvb7kzvw1";
+
+  nativeBuildInputs = [ cmake ];
+  buildInputs = [ llvm libxml2 ];
+
+  postPatch = ''
+    substituteInPlace MachO/CMakeLists.txt --replace \
+      '(''${LLVM_MAIN_SRC_DIR}/' '('
+    mkdir -p libunwind/include
+    tar -xf "${libunwind.src}" --wildcards -C libunwind/include --strip-components=2 "libunwind-*/include/"
+  '';
+
+  outputs = [ "out" "dev" ];
+
+  postInstall = ''
+    moveToOutput include "$dev"
+    moveToOutput lib "$dev"
+  '';
+
+  meta = {
+    description = "The LLVM Linker";
+    homepage    = "https://lld.llvm.org/";
+    license     = lib.licenses.ncsa;
+    platforms   = lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/12/lldb-procfs.patch b/pkgs/development/compilers/llvm/12/lldb-procfs.patch
@@ -0,0 +1,31 @@
+--- a/source/Plugins/Process/Linux/Procfs.h
++++ b/source/Plugins/Process/Linux/Procfs.h
+@@ -11,21 +11,12 @@
+ // sys/procfs.h on Android/Linux for all supported architectures.
+
+ #include <sys/ptrace.h>
++#include <asm/ptrace.h>
+
+-#ifdef __ANDROID__
+-#if defined(__arm64__) || defined(__aarch64__)
+-typedef unsigned long elf_greg_t;
+-typedef elf_greg_t
+-    elf_gregset_t[(sizeof(struct user_pt_regs) / sizeof(elf_greg_t))];
+-typedef struct user_fpsimd_state elf_fpregset_t;
+-#ifndef NT_FPREGSET
+-#define NT_FPREGSET NT_PRFPREG
+-#endif // NT_FPREGSET
+-#elif defined(__mips__)
+-#ifndef NT_FPREGSET
+-#define NT_FPREGSET NT_PRFPREG
+-#endif // NT_FPREGSET
+-#endif
+-#else // __ANDROID__
++#if !defined(__GLIBC__) && defined(__powerpc__)
++#define pt_regs musl_pt_regs
++#include <sys/procfs.h>
++#undef pt_regs
++#else
+ #include <sys/procfs.h>
+-#endif // __ANDROID__
++#endif
diff --git a/pkgs/development/compilers/llvm/12/lldb.nix b/pkgs/development/compilers/llvm/12/lldb.nix
@@ -0,0 +1,103 @@
+{ lib, stdenv
+, fetch
+, cmake
+, zlib
+, ncurses
+, swig
+, which
+, libedit
+, libxml2
+, llvm
+, clang-unwrapped
+, python3
+, version
+, libobjc
+, xpc
+, Foundation
+, bootstrap_cmds
+, Carbon
+, Cocoa
+, lit
+, enableManpages ? false
+}:
+
+stdenv.mkDerivation (rec {
+  pname = "lldb";
+  inherit version;
+
+  src = fetch pname "077fli9l0fg4kpa5l9vrj810s13ajs15d745lg4l8kmjkbw7p3yh";
+
+  patches = [ ./lldb-procfs.patch ];
+
+  nativeBuildInputs = [ cmake python3 which swig lit ]
+    ++ lib.optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
+
+  buildInputs = [
+    ncurses
+    zlib
+    libedit
+    libxml2
+    llvm
+  ]
+  ++ lib.optionals stdenv.isDarwin [
+    libobjc
+    xpc
+    Foundation
+    bootstrap_cmds
+    Carbon
+    Cocoa
+  ];
+
+  hardeningDisable = [ "format" ];
+
+  cmakeFlags = [
+    "-DLLVM_ENABLE_RTTI=OFF"
+    "-DClang_DIR=${clang-unwrapped}/lib/cmake"
+    "-DLLVM_EXTERNAL_LIT=${lit}/bin/lit"
+  ] ++ lib.optionals stdenv.isDarwin [
+    "-DLLDB_USE_SYSTEM_DEBUGSERVER=ON"
+  ] ++ lib.optionals (!stdenv.isDarwin) [
+    "-DLLDB_CODESIGN_IDENTITY=" # codesigning makes nondeterministic
+  ] ++ lib.optionals enableManpages [
+    "-DLLVM_ENABLE_SPHINX=ON"
+    "-DSPHINX_OUTPUT_MAN=ON"
+    "-DSPHINX_OUTPUT_HTML=OFF"
+  ];
+
+  postInstall = ''
+    # Editor support
+    # vscode:
+    install -D ../tools/lldb-vscode/package.json $out/share/vscode/extensions/llvm-org.lldb-vscode-0.1.0/package.json
+    mkdir -p $out/share/vscode/extensions/llvm-org.lldb-vscode-0.1.0/bin
+    ln -s $out/bin/lldb-vscode $out/share/vscode/extensions/llvm-org.lldb-vscode-0.1.0/bin
+  '';
+
+  meta = with lib; {
+    description = "A next-generation high-performance debugger";
+    homepage = "https://lldb.llvm.org";
+    license = licenses.ncsa;
+    platforms = platforms.all;
+  };
+} // lib.optionalAttrs enableManpages {
+  pname = "lldb-manpages";
+
+  buildPhase = ''
+    make docs-lldb-man
+  '';
+
+  propagatedBuildInputs = [];
+  # manually install lldb man page
+  installPhase = ''
+    mkdir -p $out/share/man/man1
+    install docs/man/lldb.1 -t $out/share/man/man1/
+  '';
+
+  postPatch = null;
+  postInstall = null;
+
+  outputs = [ "out" ];
+
+  doCheck = false;
+
+  meta.description = "man pages for LLDB ${version}";
+})
diff --git a/pkgs/development/compilers/llvm/12/llvm-outputs.patch b/pkgs/development/compilers/llvm/12/llvm-outputs.patch
@@ -0,0 +1,26 @@
+diff --git a/tools/llvm-config/llvm-config.cpp b/tools/llvm-config/llvm-config.cpp
+index 94d426b..37f7794 100644
+--- a/tools/llvm-config/llvm-config.cpp
++++ b/tools/llvm-config/llvm-config.cpp
+@@ -333,6 +333,21 @@ int main(int argc, char **argv) {
+     ActiveIncludeOption = "-I" + ActiveIncludeDir;
+   }
+
++  /// Nix-specific multiple-output handling: override ActiveLibDir if --link-shared
++  if (!IsInDevelopmentTree) {
++    bool WantShared = true;
++    for (int i = 1; i < argc; ++i) {
++      StringRef Arg = argv[i];
++      if (Arg == "--link-shared")
++        WantShared = true;
++      else if (Arg == "--link-static")
++        WantShared = false; // the last one wins
++    }
++
++    if (WantShared)
++      ActiveLibDir = std::string("@lib@") + "/lib" + LLVM_LIBDIR_SUFFIX;
++  }
++
+   /// We only use `shared library` mode in cases where the static library form
+   /// of the components provided are not available; note however that this is
+   /// skipped if we're run from within the build dir. However, once installed,
diff --git a/pkgs/development/compilers/llvm/12/llvm.nix b/pkgs/development/compilers/llvm/12/llvm.nix
@@ -0,0 +1,189 @@
+{ lib, stdenv
+, fetch
+, cmake
+, python3
+, libffi
+, libbfd
+, libpfm
+, libxml2
+, ncurses
+, version
+, release_version
+, zlib
+, buildPackages
+, debugVersion ? false
+, enableManpages ? false
+, enableSharedLibraries ? true
+, enablePFM ? !(stdenv.isDarwin
+  || stdenv.isAarch64 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
+  || stdenv.isAarch32 # broken for the armv7l builder
+)
+, enablePolly ? false
+}:
+
+let
+  inherit (lib) optional optionals optionalString;
+
+  # Used when creating a version-suffixed symlink of libLLVM.dylib
+  shortVersion = with lib;
+    concatStringsSep "." (take 1 (splitString "." release_version));
+
+in stdenv.mkDerivation (rec {
+  pname = "llvm";
+  inherit version;
+
+  src = fetch pname "1lpdkndjb8cxpcyjv9glqp58687j8y8cvd7r72pw6sbqkkzq86g5";
+  polly_src = fetch "polly" "002a8q3lgspvqdb8fi09cl11x438x6a2d2sb026jargrx92i5vas";
+
+  unpackPhase = ''
+    unpackFile $src
+    mv llvm-${release_version}* llvm
+    sourceRoot=$PWD/llvm
+  '' + optionalString enablePolly ''
+    unpackFile $polly_src
+    mv polly-* $sourceRoot/tools/polly
+  '';
+
+  outputs = [ "out" "python" ]
+    ++ optional enableSharedLibraries "lib";
+
+  nativeBuildInputs = [ cmake python3 ]
+    ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
+
+  buildInputs = [ libxml2 libffi ]
+    ++ optional enablePFM libpfm; # exegesis
+
+  propagatedBuildInputs = [ ncurses zlib ];
+
+  postPatch = optionalString stdenv.isDarwin ''
+    substituteInPlace cmake/modules/AddLLVM.cmake \
+      --replace 'set(_install_name_dir INSTALL_NAME_DIR "@rpath")' "set(_install_name_dir)" \
+      --replace 'set(_install_rpath "@loader_path/../lib''${LLVM_LIBDIR_SUFFIX}" ''${extra_libdir})' ""
+  ''
+  # Patch llvm-config to return correct library path based on --link-{shared,static}.
+  + optionalString (enableSharedLibraries) ''
+    substitute '${./llvm-outputs.patch}' ./llvm-outputs.patch --subst-var lib
+    patch -p1 < ./llvm-outputs.patch
+  '' + ''
+    # FileSystem permissions tests fail with various special bits
+    substituteInPlace unittests/Support/CMakeLists.txt \
+      --replace "Path.cpp" ""
+    rm unittests/Support/Path.cpp
+    substituteInPlace unittests/IR/CMakeLists.txt \
+      --replace "PassBuilderCallbacksTest.cpp" ""
+    rm unittests/IR/PassBuilderCallbacksTest.cpp
+  '' + optionalString stdenv.hostPlatform.isMusl ''
+    patch -p1 -i ${../TLI-musl.patch}
+    substituteInPlace unittests/Support/CMakeLists.txt \
+      --replace "add_subdirectory(DynamicLibrary)" ""
+    rm unittests/Support/DynamicLibrary/DynamicLibraryTest.cpp
+    # valgrind unhappy with musl or glibc, but fails w/musl only
+    rm test/CodeGen/AArch64/wineh4.mir
+  '' + optionalString stdenv.hostPlatform.isAarch32 ''
+    # skip failing X86 test cases on 32-bit ARM
+    rm test/DebugInfo/X86/convert-debugloc.ll
+    rm test/DebugInfo/X86/convert-inlined.ll
+    rm test/DebugInfo/X86/convert-linked.ll
+    rm test/tools/dsymutil/X86/op-convert.test
+  '' + optionalString (stdenv.hostPlatform.system == "armv6l-linux") ''
+    # Seems to require certain floating point hardware (NEON?)
+    rm test/ExecutionEngine/frem.ll
+  '' + ''
+    patchShebangs test/BugPoint/compile-custom.ll.py
+  '';
+
+  # hacky fix: created binaries need to be run before installation
+  preBuild = ''
+    mkdir -p $out/
+    ln -sv $PWD/lib $out
+  '';
+
+  # E.g. mesa.drivers use the build-id as a cache key (see #93946):
+  LDFLAGS = optionalString (enableSharedLibraries && !stdenv.isDarwin) "-Wl,--build-id=sha1";
+
+  cmakeFlags = with stdenv; [
+    "-DCMAKE_BUILD_TYPE=${if debugVersion then "Debug" else "Release"}"
+    "-DLLVM_INSTALL_UTILS=ON"  # Needed by rustc
+    "-DLLVM_BUILD_TESTS=ON"
+    "-DLLVM_ENABLE_FFI=ON"
+    "-DLLVM_ENABLE_RTTI=ON"
+    "-DLLVM_HOST_TRIPLE=${stdenv.hostPlatform.config}"
+    "-DLLVM_DEFAULT_TARGET_TRIPLE=${stdenv.hostPlatform.config}"
+    "-DLLVM_ENABLE_DUMP=ON"
+  ] ++ optionals enableSharedLibraries [
+    "-DLLVM_LINK_LLVM_DYLIB=ON"
+  ] ++ optionals enableManpages [
+    "-DLLVM_BUILD_DOCS=ON"
+    "-DLLVM_ENABLE_SPHINX=ON"
+    "-DSPHINX_OUTPUT_MAN=ON"
+    "-DSPHINX_OUTPUT_HTML=OFF"
+    "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
+  ] ++ optionals (!isDarwin) [
+    "-DLLVM_BINUTILS_INCDIR=${libbfd.dev}/include"
+  ] ++ optionals isDarwin [
+    "-DLLVM_ENABLE_LIBCXX=ON"
+    "-DCAN_TARGET_i386=false"
+  ] ++ optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    "-DCMAKE_CROSSCOMPILING=True"
+    "-DLLVM_TABLEGEN=${buildPackages.llvm_12}/bin/llvm-tblgen"
+  ];
+
+  postBuild = ''
+    rm -R $out
+  '';
+
+  preCheck = ''
+    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}$PWD/lib
+  '';
+
+  postInstall = ''
+    mkdir -p $python/share
+    mv $out/share/opt-viewer $python/share/opt-viewer
+  ''
+  + optionalString enableSharedLibraries ''
+    moveToOutput "lib/libLLVM-*" "$lib"
+    moveToOutput "lib/libLLVM${stdenv.hostPlatform.extensions.sharedLibrary}" "$lib"
+  ''
+  + optionalString (enableSharedLibraries && (!stdenv.isDarwin)) ''
+    substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
+      --replace "\''${_IMPORT_PREFIX}/lib/libLLVM-" "$lib/lib/libLLVM-"
+  ''
+  + optionalString (stdenv.isDarwin && enableSharedLibraries) ''
+    substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
+      --replace "\''${_IMPORT_PREFIX}/lib/libLLVM.dylib" "$lib/lib/libLLVM.dylib"
+    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${shortVersion}.dylib
+    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${release_version}.dylib
+  '';
+
+  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl);
+
+  checkTarget = "check-all";
+
+  requiredSystemFeatures = [ "big-parallel" ];
+  meta = {
+    description = "Collection of modular and reusable compiler and toolchain technologies";
+    homepage    = "https://llvm.org/";
+    license     = lib.licenses.ncsa;
+    maintainers = with lib.maintainers; [ lovek323 raskin dtzWill primeos ];
+    platforms   = lib.platforms.all;
+  };
+} // lib.optionalAttrs enableManpages {
+  pname = "llvm-manpages";
+
+  buildPhase = ''
+    make docs-llvm-man
+  '';
+
+  installPhase = ''
+    make -C docs install
+  '';
+
+  postPatch = null;
+  postInstall = null;
+
+  outputs = [ "out" ];
+
+  doCheck = false;
+
+  meta.description = "man pages for LLVM ${version}";
+})
diff --git a/pkgs/development/compilers/llvm/12/openmp.nix b/pkgs/development/compilers/llvm/12/openmp.nix
@@ -0,0 +1,35 @@
+{ lib
+, stdenv
+, fetch
+, fetchpatch
+, cmake
+, llvm
+, perl
+, version
+}:
+
+stdenv.mkDerivation rec {
+  pname = "openmp";
+  inherit version;
+
+  src = fetch pname "0kw1g7ndvwi0g7lx5d55mp81h9vffxz820l9r2wjdvvfs3dsyq05";
+
+  patches = [
+    # Fix compilation on aarch64-darwin, remove after the next release.
+    (fetchpatch {
+      url = "https://github.com/llvm/llvm-project/commit/7b5254223acbf2ef9cd278070c5a84ab278d7e5f.patch";
+      sha256 = "sha256-A+9/IVIoazu68FK5H5CiXcOEYe1Hpp4xTx2mIw7m8Es=";
+      stripLen = 1;
+    })
+  ];
+
+  nativeBuildInputs = [ cmake perl ];
+  buildInputs = [ llvm ];
+
+  meta = {
+    description = "Components required to build an executable OpenMP program";
+    homepage    = "https://openmp.llvm.org/";
+    license     = lib.licenses.mit;
+    platforms   = lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/12/sanitizers-nongnu.patch b/pkgs/development/compilers/llvm/12/sanitizers-nongnu.patch
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
@@ -9926,6 +9926,7 @@ in
     };
   };
 
+  clang_12 = llvmPackages_12.clang;
   clang_11 = llvmPackages_11.clang;
   clang_10 = llvmPackages_10.clang;
   clang_9  = llvmPackages_9.clang;
@@ -10803,6 +10804,7 @@ in
   lld_9 = llvmPackages_9.lld;
   lld_10 = llvmPackages_10.lld;
   lld_11 = llvmPackages_11.lld;
+  lld_12 = llvmPackages_12.lld;
 
   lldb = llvmPackages_latest.lldb;
   lldb_5 = llvmPackages_5.lldb;
@@ -10812,10 +10814,12 @@ in
   lldb_9 = llvmPackages_9.lldb;
   lldb_10 = llvmPackages_10.lldb;
   lldb_11 = llvmPackages_11.lldb;
+  lldb_12 = llvmPackages_12.lldb;
 
   llvm = llvmPackages.llvm;
   llvm-manpages = llvmPackages.llvm-manpages;
 
+  llvm_12 = llvmPackages_12.llvm;
   llvm_11 = llvmPackages_11.llvm;
   llvm_10 = llvmPackages_10.llvm;
   llvm_9  = llvmPackages_9.llvm;
@@ -10880,6 +10884,14 @@ in
     stdenv = gcc7Stdenv;
   }));
 
+  llvmPackages_12 = callPackage ../development/compilers/llvm/12 ({
+    inherit (stdenvAdapters) overrideCC;
+    buildLlvmTools = buildPackages.llvmPackages_12.tools;
+    targetLlvmLibraries = targetPackages.llvmPackages_12.libraries;
+  } // lib.optionalAttrs (stdenv.hostPlatform.isi686 && buildPackages.stdenv.cc.isGNU) {
+    stdenv = gcc7Stdenv;
+  });
+
   llvmPackages_latest = llvmPackages_11;
 
   llvmPackages_rocm = recurseIntoAttrs (callPackage ../development/compilers/llvm/rocm { });