[llvm] [CMake][LIT] Add option to run lit testsuites in parallel (PR #82899)

[Patrick Dougherty via llvm-commits]

https://github.com/patrickdoc created https://github.com/llvm/llvm-project/pull/82899

Currently `add_lit_target` sets the `USES_TERMINAL` CMake option. When using Ninja, this forces all lit testsuite targets into the single-threaded `console` pool.

This PR adds a new option `LLVM_PARALLEL_LIT` which drops the `USES_TERMINAL` flag, allowing Ninja to run them in parallel.

The default setting (`LLVM_PARALLEL_LIT=OFF`) retains the existing behavior of serial testsuite execution.

>From 209682d70af3d2f7ef206fa35551e8432089ae83 Mon Sep 17 00:00:00 2001
From: Patrick Dougherty <patrick.dougherty at modular.com>
Date: Sat, 24 Feb 2024 17:31:47 -0600
Subject: [PATCH] [CMake][LIT] Add option to run lit testsuites in parallel

---
 llvm/CMakeLists.txt              |  2 ++
 llvm/cmake/modules/AddLLVM.cmake | 17 ++++++++++++-----
 llvm/docs/CMake.rst              |  6 ++++++
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index f5f7d3f3253fd3..651f17879fad24 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -718,6 +718,8 @@ if(LLVM_INDIVIDUAL_TEST_COVERAGE)
 endif()
 set(LLVM_LIT_ARGS "${LIT_ARGS_DEFAULT}" CACHE STRING "Default options for lit")
 
+option(LLVM_PARALLEL_LIT "Enable multiple lit suites to run in parallel" OFF)
+
 # On Win32 hosts, provide an option to specify the path to the GnuWin32 tools.
 if( WIN32 AND NOT CYGWIN )
   set(LLVM_LIT_TOOLS_DIR "" CACHE PATH "Path to GnuWin32 tools")
diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index 3bc78b0dc9355a..0f1734a64ee6e6 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -1947,11 +1947,18 @@ function(add_lit_target target comment)
     list(APPEND LIT_COMMAND --param ${param})
   endforeach()
   if (ARG_UNPARSED_ARGUMENTS)
-    add_custom_target(${target}
-      COMMAND ${LIT_COMMAND} ${ARG_UNPARSED_ARGUMENTS}
-      COMMENT "${comment}"
-      USES_TERMINAL
-      )
+    if (LLVM_PARALLEL_LIT)
+     add_custom_target(${target}
+       COMMAND ${LIT_COMMAND} ${ARG_UNPARSED_ARGUMENTS}
+       COMMENT "${comment}"
+       )
+    else()
+     add_custom_target(${target}
+       COMMAND ${LIT_COMMAND} ${ARG_UNPARSED_ARGUMENTS}
+       COMMENT "${comment}"
+       USES_TERMINAL
+       )
+    endif()
   else()
     add_custom_target(${target}
       COMMAND ${CMAKE_COMMAND} -E echo "${target} does nothing, no tools built.")
diff --git a/llvm/docs/CMake.rst b/llvm/docs/CMake.rst
index abef4f8103140f..35c47989a7eef0 100644
--- a/llvm/docs/CMake.rst
+++ b/llvm/docs/CMake.rst
@@ -762,6 +762,12 @@ enabled sub-projects. Nearly all of these variable names begin with
 **LLVM_PARALLEL_LINK_JOBS**:STRING
   Define the maximum number of concurrent link jobs.
 
+**LLVM_PARALLEL_LIT**:BOOL
+  Defaults to ``OFF``. If set to ``OFF``, lit testsuites will be configured
+  with CMake's ``USES_TERMINAL`` flag to give direct access to the terminal. If
+  set to ``ON``, that flag will be removed allowing Ninja to schedule multiple
+  lit testsuites in parallel.
+
 **LLVM_RAM_PER_COMPILE_JOB**:STRING
   Calculates the amount of Ninja compile jobs according to available resources.
   Value has to be in MB, overwrites LLVM_PARALLEL_COMPILE_JOBS. Compile jobs