diff --git a/pkgs/development/compilers/llvm/6/clang/default.nix b/pkgs/development/compilers/llvm/6/clang/default.nix
index 0ee1404484b9..5ef97ef7d82e 100644
--- a/pkgs/development/compilers/llvm/6/clang/default.nix
+++ b/pkgs/development/compilers/llvm/6/clang/default.nix
@@ -9,7 +9,7 @@ let
     name = "clang-${version}";
 
     unpackPhase = ''
-      unpackFile ${fetch "cfe" "1zyh4dggxd55lnfg73c8fybnkssqcaa6bq2h4bzimnnj1jdnqpqk"}
+      unpackFile ${fetch "cfe" "1mrj0ig9x5dxvglmkyw6i8yb9hvznywqn2g6lqaw7a5fhjjdq0x2"}
       mv cfe-${version}* clang
       sourceRoot=$PWD/clang
       unpackFile ${clang-tools-extra_src}
diff --git a/pkgs/development/compilers/llvm/6/default.nix b/pkgs/development/compilers/llvm/6/default.nix
index 13e1d2308f8c..3fa53f7281e4 100644
--- a/pkgs/development/compilers/llvm/6/default.nix
+++ b/pkgs/development/compilers/llvm/6/default.nix
@@ -6,16 +6,16 @@
 let
   callPackage = newScope (self // { inherit stdenv cmake libxml2 python2 isl release_version version fetch; });
 
-  release_version = "5.0.1";
-  version = release_version; # differentiating these is important for rc's
+  release_version = "6.0.0";
+  version = "6.0.0rc1"; # differentiating these is important for rc's
 
   fetch = name: sha256: fetchurl {
-    url = "http://llvm.org/releases/${release_version}/${name}-${version}.src.tar.xz";
+    url = "http://prereleases.llvm.org/${release_version}/rc1/${name}-${version}.src.tar.xz";
     inherit sha256;
   };
 
-  compiler-rt_src = fetch "compiler-rt" "1nlmm0b3wpdwxkldqp1klzv3rpqf94q2a248xgqb7aapyhbi9paf";
-  clang-tools-extra_src = fetch "clang-tools-extra" "09fjii7w43kvxvsxxs6gig9vz95vnvx1779rqd36h8kksvws3bcs";
+  compiler-rt_src = fetch "compiler-rt" "08dwlax5sfmpzwfbzdwig9hbmrqzlq2332rb5yh0l5xrp0y5869z";
+  clang-tools-extra_src = fetch "clang-tools-extra" "1rj4b6cqn05s2b3qiw7iadc8a1hrn4vs6g06nwxmqwpx3790dqyn";
 
   # Add man output without introducing extra dependencies.
   overrideManOutput = drv:
diff --git a/pkgs/development/compilers/llvm/6/libc++/default.nix b/pkgs/development/compilers/llvm/6/libc++/default.nix
index 6f03e225ad65..e0294430a267 100644
--- a/pkgs/development/compilers/llvm/6/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/6/libc++/default.nix
@@ -3,7 +3,7 @@
 stdenv.mkDerivation rec {
   name = "libc++-${version}";
 
-  src = fetch "libcxx" "003wwniwlikgh38cbqbcshc5gkiv3a2jkmbn6am9s46y5gfrk3zs";
+  src = fetch "libcxx" "0l026xx364a6zbx8sbd3280wbag0pkmj342v8zh1lg0661w52l8d";
 
   postUnpack = ''
     unpackFile ${libcxxabi.src}
diff --git a/pkgs/development/compilers/llvm/6/libc++abi.nix b/pkgs/development/compilers/llvm/6/libc++abi.nix
index 166f4260291f..3ffd5637ee0d 100644
--- a/pkgs/development/compilers/llvm/6/libc++abi.nix
+++ b/pkgs/development/compilers/llvm/6/libc++abi.nix
@@ -3,7 +3,7 @@
 stdenv.mkDerivation {
   name = "libc++abi-${version}";
 
-  src = fetch "libcxxabi" "0m78yr4arlz2b9m96xcygk15m2pbz8i10snk78i3q7pjnwn1a9as";
+  src = fetch "libcxxabi" "0kmfmxm3iph9l1ndj2z7gj52n8bmy0rnnxzidfbliays2qzbwrsk";
 
   nativeBuildInputs = [ cmake ];
   buildInputs = stdenv.lib.optional (!stdenv.isDarwin && !stdenv.isFreeBSD) libunwind;
diff --git a/pkgs/development/compilers/llvm/6/lld.nix b/pkgs/development/compilers/llvm/6/lld.nix
index 1d00b16cce1f..2b3d6aadd7f2 100644
--- a/pkgs/development/compilers/llvm/6/lld.nix
+++ b/pkgs/development/compilers/llvm/6/lld.nix
@@ -10,7 +10,7 @@
 stdenv.mkDerivation {
   name = "lld-${version}";
 
-  src = fetch "lld" "15fq2zvkliyiw5qi7ig2r8bshgbz4kzvs5in16mhfkw20l06rcym";
+  src = fetch "lld" "1yzq762bh375sskjgkcr0vqlhlii2br86z8wi2jbxmml0pj0xn99";
 
   nativeBuildInputs = [ cmake ];
   buildInputs = [ llvm ];
diff --git a/pkgs/development/compilers/llvm/6/lldb.nix b/pkgs/development/compilers/llvm/6/lldb.nix
index 559c52831cd2..fa9bde903f6c 100644
--- a/pkgs/development/compilers/llvm/6/lldb.nix
+++ b/pkgs/development/compilers/llvm/6/lldb.nix
@@ -17,7 +17,7 @@
 stdenv.mkDerivation {
   name = "lldb-${version}";
 
-  src = fetch "lldb" "0sipv8k37ai44m7jcf6wsbm2q41dgk3sk9m3i6823jkmg7kckhdp";
+  src = fetch "lldb" "1a0bmk0p4rclk0wvfg2ga4wkqp8lm6l3wx6g4g4dgiavd4bgsgl4";
 
   postPatch = ''
     # Fix up various paths that assume llvm and clang are installed in the same place
diff --git a/pkgs/development/compilers/llvm/6/llvm.nix b/pkgs/development/compilers/llvm/6/llvm.nix
index 400ffa341171..4aba455c4c9f 100644
--- a/pkgs/development/compilers/llvm/6/llvm.nix
+++ b/pkgs/development/compilers/llvm/6/llvm.nix
@@ -22,7 +22,7 @@
 }:
 
 let
-  src = fetch "llvm" "1c07i0b61j69m578lgjkyayg419sh7sn40xb3j112nr2q2gli9sz";
+  src = fetch "llvm" "0dsik1l6jshd617fh4qs1373s6dfkq4gsjhyf6zq2qb6kyisy2vd";
 
   # Used when creating a version-suffixed symlink of libLLVM.dylib
   shortVersion = with stdenv.lib;
diff --git a/pkgs/development/compilers/llvm/6/openmp.nix b/pkgs/development/compilers/llvm/6/openmp.nix
index 5a01c191b5ae..f4c2a3f160a0 100644
--- a/pkgs/development/compilers/llvm/6/openmp.nix
+++ b/pkgs/development/compilers/llvm/6/openmp.nix
@@ -10,7 +10,7 @@
 stdenv.mkDerivation {
   name = "openmp-${version}";
 
-  src = fetch "openmp" "0lr6r87xzg87w1q9rrh04nqpyr8c929dh4qy3csjiy7rsb6kbdmd";
+  src = fetch "openmp" "0infci57hr89nxgs3v34z87kaqdw9pdkr6apyywkb8av032rhhpf";
 
   nativeBuildInputs = [ cmake perl ];
   buildInputs = [ llvm ];
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index b83424eabbad..2f49e02e34c9 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -5780,6 +5780,7 @@ with pkgs;
     };
   };
 
+  clang_6  = llvmPackages_6.clang;
   clang_5  = llvmPackages_5.clang;
   clang_4  = llvmPackages_4.clang;
   clang_39 = llvmPackages_39.clang;
@@ -6465,13 +6466,16 @@ with pkgs;
   lld = llvmPackages.lld;
   lld_4 = llvmPackages_4.lld;
   lld_5 = llvmPackages_5.lld;
+  lld_6 = llvmPackages_6.lld;
 
   lldb = llvmPackages.lldb;
   lldb_4 = llvmPackages_4.lldb;
   lldb_5 = llvmPackages_5.lldb;
+  lldb_6 = llvmPackages_6.lldb;
 
   llvm = llvmPackages.llvm;
 
+  llvm_6  = llvmPackages_6.llvm;
   llvm_5  = llvmPackages_5.llvm;
   llvm_4  = llvmPackages_4.llvm;
   llvm_39 = llvmPackages_39.llvm;
@@ -6535,6 +6539,9 @@ with pkgs;
     stdenv = overrideCC stdenv gcc6; # with gcc-7: undefined reference to `__divmoddi4'
   });
 
+  llvmPackages_6 = callPackage ../development/compilers/llvm/6 {
+    inherit (stdenvAdapters) overrideCC;
+  };
   manticore = callPackage ../development/compilers/manticore { };
 
   mentorToolchains = recurseIntoAttrs (