[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, 9 insertions, 1 deletions

diff --git a/llvm/lib/Support/Windows/Host.inc b/llvm/lib/Support/Windows/Host.inc
index fe89fe0aad8..7e196cf0ce1 100644
--- a/llvm/lib/Support/Windows/Host.inc
+++ b/llvm/lib/Support/Windows/Host.inc
@@ -18,5 +18,13 @@
 using namespace llvm;
 
 std::string sys::getDefaultTargetTriple() {
-  return Triple::normalize(LLVM_DEFAULT_TARGET_TRIPLE);
+  const char *Triple = LLVM_DEFAULT_TARGET_TRIPLE;
+
+  // Override the default target with an environment variable named by LLVM_TARGET_TRIPLE_ENV.
+#if defined(LLVM_TARGET_TRIPLE_ENV)
+  if (const char *EnvTriple = std::getenv(LLVM_TARGET_TRIPLE_ENV))
+    Triple = EnvTriple;
+#endif
+
+  return Triple::normalize(Triple);
 }