[CMake] Introduce LLVM_TARGET_TRIPLE_ENV as an option to override LLVM_DEFAULT_TARGET_TRIPLE at runtime.

No behavior is changed if LLVM_TARGET_TRIPLE_ENV is blank or undefined.

If LLVM_TARGET_TRIPLE_ENV is "TEST_TARGET_TRIPLE" and $TEST_TARGET_TRIPLE is not blank,
llvm::sys::getDefaultTargetTriple() returns $TEST_TARGET_TRIPLE.
Lit resets config.target_triple and config.environment[LLVM_TARGET_TRIPLE_ENV] to change the default target.

Without changing LLVM_DEFAULT_TARGET_TRIPLE nor rebuilding, lit can be run;

  TEST_TARGET_TRIPLE=i686-pc-win32 bin/llvm-lit -sv path/to/test/
  TEST_TARGET_TRIPLE=i686-pc-win32 ninja check-clang-tools

Differential Revision: https://reviews.llvm.org/D33662

llvm-svn: 305632

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index e011bb40275..2b54bdbf290 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -1133,6 +1133,19 @@ function(configure_lit_site_cfg input output)
 
   set(LIT_SITE_CFG_IN_HEADER  "## Autogenerated from ${input}\n## Do not edit!")
 
+  # Override config_target_triple (and the env)
+  if(LLVM_TARGET_TRIPLE_ENV)
+    # This is expanded into the heading.
+    string(CONCAT LIT_SITE_CFG_IN_HEADER "${LIT_SITE_CFG_IN_HEADER}\n\n"
+      "import os\n"
+      "target_env = \"${LLVM_TARGET_TRIPLE_ENV}\"\n"
+      "config.target_triple = config.environment[target_env] = os.environ.get(target_env, \"${TARGET_TRIPLE}\")\n"
+      )
+
+    # This is expanded to; config.target_triple = ""+config.target_triple+""
+    set(TARGET_TRIPLE "\"+config.target_triple+\"")
+  endif()
+
   configure_file(${input} ${output} @ONLY)
 endfunction()