Index: llvm/utils/lit/lit/TestRunner.py
===================================================================
--- llvm/utils/lit/lit/TestRunner.py
+++ llvm/utils/lit/lit/TestRunner.py
@@ -236,7 +236,9 @@
     return ''.join(result)
 
 # args are from 'export' or 'env' command.
-# Returns copy of args without those commands or their arguments.
+# Skips the command, and parses its arguments.
+# Modifies env accordingly if env is not None.
+# Returns copy of args without the command or its arguments.
 def updateEnv(env, args):
     arg_idx_next = len(args)
     unset_next_env_var = False
@@ -249,7 +251,7 @@
             continue
         if unset_next_env_var:
             unset_next_env_var = False
-            if arg in env.env:
+            if env is not None and arg in env.env:
                 del env.env[arg]
             continue
 
@@ -259,7 +261,8 @@
         if eq == '':
             arg_idx_next = arg_idx + 1
             break
-        env.env[key] = val
+        if env is not None:
+            env.env[key] = val
     return args[arg_idx_next:]
 
 def executeBuiltinEcho(cmd, shenv):
@@ -796,7 +799,24 @@
     assert isinstance(cmd, ShUtil.Pipeline)
 
     # Handle shell builtins first.
-    if cmd.commands[0].args[0] == 'cd':
+
+    # Extract env commands and their arguments so we don't overlook any shell
+    # builtin.  Don't modify the original args as we'll need to process the
+    # env commands again if this is not a shell builtin.
+    #
+    # env calling a builtin is useless, so each shell builtin takes the safe
+    # approach of complaining about env.
+    cmd0_has_envs = False
+    cmd0_args_pruned = list(cmd.commands[0].args)
+    while cmd0_args_pruned[0] == 'env':
+        cmd0_args_pruned = updateEnv(None, cmd0_args_pruned)
+        if not cmd0_args_pruned:
+            raise ValueError("'env' requires a subcommand")
+        cmd0_has_envs = True
+
+    if cmd0_args_pruned[0] == 'cd':
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call 'cd'")
         if len(cmd.commands) != 1:
             raise ValueError("'cd' cannot be part of a pipeline")
         if len(cmd.commands[0].args) != 2:
@@ -816,13 +836,17 @@
     # a file.
     # FIXME: Standardize on the builtin echo implementation. We can use a
     # temporary file to sidestep blocking pipe write issues.
-    if cmd.commands[0].args[0] == 'echo' and len(cmd.commands) == 1:
+    if cmd0_args_pruned[0] == 'echo' and len(cmd.commands) == 1:
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call 'echo'")
         output = executeBuiltinEcho(cmd.commands[0], shenv)
         results.append(ShellCommandResult(cmd.commands[0], output, "", 0,
                                           False))
         return 0
 
-    if cmd.commands[0].args[0] == 'export':
+    if cmd0_args_pruned[0] == 'export':
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call 'export'")
         if len(cmd.commands) != 1:
             raise ValueError("'export' cannot be part of a pipeline")
         if len(cmd.commands[0].args) != 2:
@@ -830,7 +854,9 @@
         updateEnv(shenv, cmd.commands[0].args)
         return 0
 
-    if cmd.commands[0].args[0] == 'mkdir':
+    if cmd0_args_pruned[0] == 'mkdir':
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call 'mkdir'")
         if len(cmd.commands) != 1:
             raise InternalShellError(cmd.commands[0], "Unsupported: 'mkdir' "
                                      "cannot be part of a pipeline")
@@ -838,7 +864,9 @@
         results.append(cmdResult)
         return cmdResult.exitCode
 
-    if cmd.commands[0].args[0] == 'diff':
+    if cmd0_args_pruned[0] == 'diff':
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call 'diff'")
         if len(cmd.commands) != 1:
             raise InternalShellError(cmd.commands[0], "Unsupported: 'diff' "
                                      "cannot be part of a pipeline")
@@ -846,7 +874,9 @@
         results.append(cmdResult)
         return cmdResult.exitCode
 
-    if cmd.commands[0].args[0] == 'rm':
+    if cmd0_args_pruned[0] == 'rm':
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call 'rm'")
         if len(cmd.commands) != 1:
             raise InternalShellError(cmd.commands[0], "Unsupported: 'rm' "
                                      "cannot be part of a pipeline")
@@ -854,7 +884,9 @@
         results.append(cmdResult)
         return cmdResult.exitCode
 
-    if cmd.commands[0].args[0] == ':':
+    if cmd0_args_pruned[0] == ':':
+        if cmd0_has_envs:
+            raise ValueError("'env' cannot call ':'")
         if len(cmd.commands) != 1:
             raise InternalShellError(cmd.commands[0], "Unsupported: ':' "
                                      "cannot be part of a pipeline")
@@ -875,12 +907,16 @@
         # Reference the global environment by default.
         cmd_shenv = shenv
         args = list(j.args)
-        if j.args[0] == 'env':
+        while args[0] == 'env':
             # Create a copy of the global environment and modify it for this one
-            # command. There might be multiple envs in a pipeline:
+            # command. There might be multiple envs in a pipeline, and
+            # there might be multiple envs in a command (usually when one comes
+            # from a substitution):
             #   env FOO=1 llc < %s | env BAR=2 llvm-mc | FileCheck %s
-            cmd_shenv = ShellEnvironment(shenv.cwd, shenv.env)
-            args = updateEnv(cmd_shenv, j.args)
+            #   env FOO=1 %{another_env_plus_cmd} | FileCheck %s
+            if cmd_shenv is shenv:
+                cmd_shenv = ShellEnvironment(shenv.cwd, shenv.env)
+            args = updateEnv(cmd_shenv, args)
             if not args:
                 raise ValueError("'env' requires a subcommand")
 
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-args-nested-none.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-args-nested-none.txt
@@ -0,0 +1 @@
+# RUN: env env env
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-cd.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-cd.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 cd foobar
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-colon.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-colon.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 :
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-diff.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-diff.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 diff foo.txt bar.txt
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-echo.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-echo.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 echo hello world
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-env.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-env.txt
@@ -0,0 +1,32 @@
+# Check that internal env can call internal env.
+
+# RUN: env env %{python} print_environment.py \
+# RUN: | FileCheck -check-prefix=CHECK-2-EMPTY %s
+#
+# CHECK-2-EMPTY: BAR = 2
+# CHECK-2-EMPTY: FOO = 1
+
+# RUN: env FOO=2 env BAR=1 %{python} print_environment.py \
+# RUN: | FileCheck -check-prefix=CHECK-2-VAL %s
+#
+# CHECK-2-VAL: BAR = 1
+# CHECK-2-VAL: FOO = 2
+
+# RUN: env -u FOO env -u BAR %{python} print_environment.py \
+# RUN: | FileCheck -check-prefix=CHECK-2-U %s
+#
+# CHECK-2-U-NOT: BAR
+# CHECK-2-U-NOT: FOO
+
+# RUN: env -u FOO BAR=1 env -u BAR FOO=2 %{python} print_environment.py \
+# RUN: | FileCheck -check-prefix=CHECK-2-U-VAL %s
+#
+# CHECK-2-U-VAL-NOT: BAR
+# CHECK-2-U-VAL: FOO = 2
+
+# RUN: env -u FOO BAR=1 env -u BAR FOO=2 env BAZ=3 %{python} print_environment.py \
+# RUN: | FileCheck -check-prefix=CHECK-3 %s
+#
+# CHECK-3-NOT: BAR
+# CHECK-3: BAZ = 3
+# CHECK-3: FOO = 2
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-export.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-export.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 export BAZ=3
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-mkdir.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-mkdir.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 mkdir foobar
Index: llvm/utils/lit/tests/Inputs/shtest-env/env-calls-rm.txt
===================================================================
--- /dev/null
+++ llvm/utils/lit/tests/Inputs/shtest-env/env-calls-rm.txt
@@ -0,0 +1 @@
+# RUN: env -u FOO BAR=3 rm foobar
Index: llvm/utils/lit/tests/shtest-env.py
===================================================================
--- llvm/utils/lit/tests/shtest-env.py
+++ llvm/utils/lit/tests/shtest-env.py
@@ -7,7 +7,7 @@
 
 # Make sure env commands are included in printed commands.
 
-# CHECK: -- Testing: 7 tests{{.*}}
+# CHECK: -- Testing: 16 tests{{.*}}
 
 # CHECK: UNRESOLVED: shtest-env :: env-args-last-is-assign.txt ({{[^)]*}})
 # CHECK: ValueError: 'env' requires a subcommand
@@ -18,22 +18,57 @@
 # CHECK: UNRESOLVED: shtest-env :: env-args-last-is-u.txt ({{[^)]*}})
 # CHECK: ValueError: 'env' requires a subcommand
 
+# CHECK: UNRESOLVED: shtest-env :: env-args-nested-none.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' requires a subcommand
+
 # CHECK: UNRESOLVED: shtest-env :: env-args-none.txt ({{[^)]*}})
 # CHECK: ValueError: 'env' requires a subcommand
 
+# CHECK: UNRESOLVED: shtest-env :: env-calls-cd.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call 'cd'
+
+# CHECK: UNRESOLVED: shtest-env :: env-calls-colon.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call ':'
+
+# CHECK: UNRESOLVED: shtest-env :: env-calls-diff.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call 'diff'
+
+# CHECK: UNRESOLVED: shtest-env :: env-calls-echo.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call 'echo'
+
+# CHECK: PASS: shtest-env :: env-calls-env.txt ({{[^)]*}})
+# CHECK: $ "env" "env" "{{[^"]*}}" "print_environment.py"
+# CHECK: $ "env" "FOO=2" "env" "BAR=1" "{{[^"]*}}" "print_environment.py"
+# CHECK: $ "env" "-u" "FOO" "env" "-u" "BAR" "{{[^"]*}}" "print_environment.py"
+# CHECK: $ "env" "-u" "FOO" "BAR=1" "env" "-u" "BAR" "FOO=2" "{{[^"]*}}" "print_environment.py"
+# CHECK: $ "env" "-u" "FOO" "BAR=1" "env" "-u" "BAR" "FOO=2" "env" "BAZ=3" "{{[^"]*}}" "print_environment.py"
+# CHECK-NOT: ${{.*}}print_environment.py
+
+# CHECK: UNRESOLVED: shtest-env :: env-calls-export.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call 'export'
+
+# CHECK: UNRESOLVED: shtest-env :: env-calls-mkdir.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call 'mkdir'
+
+# CHECK: UNRESOLVED: shtest-env :: env-calls-rm.txt ({{[^)]*}})
+# CHECK: ValueError: 'env' cannot call 'rm'
+
 # CHECK: PASS: shtest-env :: env-u.txt ({{[^)]*}})
 # CHECK: $ "{{[^"]*}}" "print_environment.py"
 # CHECK: $ "env" "-u" "FOO" "{{[^"]*}}" "print_environment.py"
 # CHECK: $ "env" "-u" "FOO" "-u" "BAR" "{{[^"]*}}" "print_environment.py"
+# CHECK-NOT: ${{.*}}print_environment.py
 
 # CHECK: PASS: shtest-env :: env.txt ({{[^)]*}})
 # CHECK: $ "env" "A_FOO=999" "{{[^"]*}}" "print_environment.py"
 # CHECK: $ "env" "A_FOO=1" "B_BAR=2" "C_OOF=3" "{{[^"]*}}" "print_environment.py"
+# CHECK-NOT: ${{.*}}print_environment.py
 
 # CHECK: PASS: shtest-env :: mixed.txt ({{[^)]*}})
 # CHECK: $ "env" "A_FOO=999" "-u" "FOO" "{{[^"]*}}" "print_environment.py"
 # CHECK: $ "env" "A_FOO=1" "-u" "FOO" "B_BAR=2" "-u" "BAR" "C_OOF=3" "{{[^"]*}}" "print_environment.py"
+# CHECK-NOT: ${{.*}}print_environment.py
 
-# CHECK: Expected Passes : 3
-# CHECK: Unresolved Tests : 4
+# CHECK: Expected Passes : 4
+# CHECK: Unresolved Tests : 12
 # CHECK-NOT: {{.}}