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

[chapuni]

Summary

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

Why I make the name of an environment variable configurable? Because...

• Let this functionality configurable.
• I'd not like to hear "Why $CLANG_TARGET is unavailable in spite of $LLVM_TARGET there"

In the future, I am planning to implement running triple matrix in Lit.
For example, running each test for each triple {i686|x86_64}-{mingw32|win32}.
Then, some commands, like FileCheck and commands with an explicit triple, aren't required to run iteratively.

[beanz]

LGTM

llvm/trunk/CMakeLists.txt

if(NOT LLVM_PROFILE_FILE_PATTERN)
     endif()
   endif()
 endif()
 
 if (LLVM_BUILD_STATIC)
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static")
 endif()
 
+# Override the default target with an environment variable named by LLVM_TARGET_TRIPLE_ENV.
+set(LLVM_TARGET_TRIPLE_ENV CACHE STRING "The name of environment variable to override default target. Disabled by blank.")
+mark_as_advanced(LLVM_TARGET_TRIPLE_ENV)
+
 # All options referred to from HandleLLVMOptions have to be specified
 # BEFORE this include, otherwise options will not be correctly set on
 # first cmake run
 include(config-ix)
 
 string(REPLACE "Native" ${LLVM_NATIVE_ARCH}
   LLVM_TARGETS_TO_BUILD "${LLVM_TARGETS_TO_BUILD}")
 list(REMOVE_DUPLICATES LLVM_TARGETS_TO_BUILD)

llvm/trunk/cmake/modules/AddLLVM.cmake

function(configure_lit_site_cfg input output)
   set(HOST_ARCH ${CMAKE_SYSTEM_PROCESSOR})
 
   set(HOST_CC "${CMAKE_C_COMPILER} ${CMAKE_C_COMPILER_ARG1}")
   set(HOST_CXX "${CMAKE_CXX_COMPILER} ${CMAKE_CXX_COMPILER_ARG1}")
   set(HOST_LDFLAGS "${CMAKE_EXE_LINKER_FLAGS}")
 
   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()
 
 # A raw function to create a lit target. This is used to implement the testuite
 # management functions.
 function(add_lit_target target comment)
   cmake_parse_arguments(ARG "" "" "PARAMS;DEPENDS;ARGS" ${ARGN})
   set(LIT_ARGS "${ARG_ARGS} ${LLVM_LIT_ARGS}")

llvm/trunk/include/llvm/Config/config.h.cmake

 #cmakedefine LLVM_HOST_TRIPLE "${LLVM_HOST_TRIPLE}"
 
 /* Define if this is Unixish platform */
 #cmakedefine LLVM_ON_UNIX ${LLVM_ON_UNIX}
 
 /* Define if this is Win32ish platform */
 #cmakedefine LLVM_ON_WIN32 ${LLVM_ON_WIN32}
 
+/* Define if overriding target triple is enabled */
+#cmakedefine LLVM_TARGET_TRIPLE_ENV "${LLVM_TARGET_TRIPLE_ENV}"
+
 /* Define if we have the Intel JIT API runtime support library */
 #cmakedefine01 LLVM_USE_INTEL_JITEVENTS
 
 /* Define if we have the oprofile JIT-support library */
 #cmakedefine01 LLVM_USE_OPROFILE
 
 /* LLVM version information */
 #cmakedefine LLVM_VERSION_INFO "${LLVM_VERSION_INFO}"

llvm/trunk/lib/Support/Unix/Host.inc

std::string sys::getDefaultTargetTriple() {
   // On darwin, we want to update the version to match that of the
   // target.
   std::string::size_type DarwinDashIdx = TargetTripleString.find("-darwin");
   if (DarwinDashIdx != std::string::npos) {
     TargetTripleString.resize(DarwinDashIdx + strlen("-darwin"));
     TargetTripleString += getOSVersion();
   }
 
+  // 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))
+    TargetTripleString = EnvTriple;
+#endif
+
   return Triple::normalize(TargetTripleString);
 }

llvm/trunk/lib/Support/Windows/Host.inc

 
 #include "WindowsSupport.h"
 #include <cstdio>
 #include <string>
 
 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);
 }