diff --git a/pkgs/development/compilers/llvm/10/llvm/default.nix b/pkgs/development/compilers/llvm/10/llvm/default.nix
index 41c20ac47ebf..fba387adf867 100644
--- a/pkgs/development/compilers/llvm/10/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/10/llvm/default.nix
@@ -15,6 +15,8 @@
 , zlib
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -30,6 +32,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -48,7 +73,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -255,8 +280,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/11/llvm/default.nix b/pkgs/development/compilers/llvm/11/llvm/default.nix
index 93cf2757c652..df9749fe1c27 100644
--- a/pkgs/development/compilers/llvm/11/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/11/llvm/default.nix
@@ -15,6 +15,8 @@
 , zlib
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl) && (!stdenv.hostPlatform.isRiscV)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -30,6 +32,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -48,7 +73,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -267,8 +292,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl) && (!stdenv.hostPlatform.isRiscV)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/12/llvm/default.nix b/pkgs/development/compilers/llvm/12/llvm/default.nix
index 3d5592e19ee5..2d7f70540dd8 100644
--- a/pkgs/development/compilers/llvm/12/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/12/llvm/default.nix
@@ -15,6 +15,8 @@
 , zlib
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -30,6 +32,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -48,7 +73,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -255,8 +280,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/13/llvm/default.nix b/pkgs/development/compilers/llvm/13/llvm/default.nix
index e2d6da816f32..f3a9ced70e19 100644
--- a/pkgs/development/compilers/llvm/13/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/13/llvm/default.nix
@@ -16,6 +16,8 @@
 , which
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -31,6 +33,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -40,7 +65,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -217,8 +242,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/14/llvm/default.nix b/pkgs/development/compilers/llvm/14/llvm/default.nix
index 9bd24b9ac068..e4c004d24ac3 100644
--- a/pkgs/development/compilers/llvm/14/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/14/llvm/default.nix
@@ -17,6 +17,8 @@
 , which
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -32,6 +34,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -50,7 +75,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -230,8 +255,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/6/llvm/default.nix b/pkgs/development/compilers/llvm/6/llvm/default.nix
index 954887cd2368..22a3970f76ce 100644
--- a/pkgs/development/compilers/llvm/6/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/6/llvm/default.nix
@@ -13,6 +13,8 @@
 , zlib
 , buildLlvmTools
 , fetchpatch
+, doCheck ? stdenv.isLinux && (!stdenv.isi686)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , debugVersion ? false
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
@@ -26,6 +28,29 @@ let
   versionSuffixes = with lib;
     let parts = splitVersion release_version; in
     imap (i: _: concatStringsSep "." (take i parts)) parts;
+
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
 in
 
 stdenv.mkDerivation (rec {
@@ -46,7 +71,7 @@ stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optional enableManpages python3.pkgs.sphinx;
 
   buildInputs = [ libxml2 libffi ];
@@ -227,8 +252,7 @@ stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isi686)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/7/llvm/default.nix b/pkgs/development/compilers/llvm/7/llvm/default.nix
index eaeef3c2ef50..185ae884442e 100644
--- a/pkgs/development/compilers/llvm/7/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/7/llvm/default.nix
@@ -15,6 +15,8 @@
 , zlib
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -31,6 +33,29 @@ let
     let parts = splitVersion release_version; in
     imap (i: _: concatStringsSep "." (take i parts)) parts;
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -49,7 +74,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optional enableManpages python3.pkgs.sphinx;
 
   buildInputs = [ libxml2 libffi ]
@@ -245,8 +270,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/8/llvm/default.nix b/pkgs/development/compilers/llvm/8/llvm/default.nix
index aa76fc0c3cf7..3b0877115e06 100644
--- a/pkgs/development/compilers/llvm/8/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/8/llvm/default.nix
@@ -15,6 +15,8 @@
 , zlib
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -30,6 +32,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitVersion release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -48,7 +73,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -237,8 +262,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/9/llvm/default.nix b/pkgs/development/compilers/llvm/9/llvm/default.nix
index 89bc014f5c65..0838fd8c5844 100644
--- a/pkgs/development/compilers/llvm/9/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/9/llvm/default.nix
@@ -15,6 +15,8 @@
 , zlib
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isRiscV)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
@@ -30,6 +32,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -48,7 +73,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake python3 ]
+  nativeBuildInputs = [ cmake python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -252,8 +277,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isRiscV)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/git/llvm/default.nix b/pkgs/development/compilers/llvm/git/llvm/default.nix
index 140c2db71f54..1daeb745e588 100644
--- a/pkgs/development/compilers/llvm/git/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/git/llvm/default.nix
@@ -18,6 +18,8 @@
 , which
 , buildLlvmTools
 , debugVersion ? false
+, doCheck ? stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
+  && (stdenv.hostPlatform == stdenv.buildPlatform)
 , enableManpages ? false
 , enableSharedLibraries ? !stdenv.hostPlatform.isStatic
 , enablePFM ? !(stdenv.isDarwin
@@ -34,6 +36,29 @@ let
   shortVersion = with lib;
     concatStringsSep "." (take 1 (splitString "." release_version));
 
+  # Ordinarily we would just the `doCheck` and `checkDeps` functionality
+  # `mkDerivation` gives us to manage our test dependencies (instead of breaking
+  # out `doCheck` as a package level attribute).
+  #
+  # Unfortunately `lit` does not forward `$PYTHONPATH` to children processes, in
+  # particular the children it uses to do feature detection.
+  #
+  # This means that python deps we add to `checkDeps` (which the python
+  # interpreter is made aware of via `$PYTHONPATH` – populated by the python
+  # setup hook) are not picked up by `lit` which causes it to skip tests.
+  #
+  # Adding `python3.withPackages (ps: [ ... ])` to `checkDeps` also doesn't work
+  # because this package is shadowed in `$PATH` by the regular `python3`
+  # package.
+  #
+  # So, we "manually" assemble one python derivation for the package to depend
+  # on, taking into account whether checks are enabled or not:
+  python = if doCheck then
+    let
+      checkDeps = ps: with ps; [ psutil ];
+    in python3.withPackages checkDeps
+  else python3;
+
 in stdenv.mkDerivation (rec {
   pname = "llvm";
   inherit version;
@@ -52,7 +77,7 @@ in stdenv.mkDerivation (rec {
 
   outputs = [ "out" "lib" "dev" "python" ];
 
-  nativeBuildInputs = [ cmake ninja python3 ]
+  nativeBuildInputs = [ cmake ninja python ]
     ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
 
   buildInputs = [ libxml2 libffi ]
@@ -217,8 +242,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl)
-    && (stdenv.hostPlatform == stdenv.buildPlatform);
+  inherit doCheck;
 
   checkTarget = "check-all";