[Offload] Detect target triple from preprocessor instead of CMake (#91283)

Summary:
This patch removes the special-case handling for the target triple
inside of the CMake. I moved it into the implementation so it's easier
to see and modify.

Author: jhuber6

offload/plugins-nextgen/host/CMakeLists.txt

@@ -53,36 +53,26 @@ endif()
 # Define the target specific triples and ELF machine values.
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64le$")
   target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_PPC64)
-  target_compile_definitions(omptarget.rtl.host PRIVATE
-      LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE="powerpc64le-ibm-linux-gnu")
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "powerpc64le-ibm-linux-gnu" "powerpc64le-ibm-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "ppc64$")
   target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_PPC64)
-  target_compile_definitions(omptarget.rtl.host PRIVATE
-      LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE="powerpc64-ibm-linux-gnu")
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "powerpc64-ibm-linux-gnu" "powerpc64-ibm-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64$")
   target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_X86_64)
-  target_compile_definitions(omptarget.rtl.host PRIVATE
-      LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE="x86_64-pc-linux-gnu")
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "x86_64-pc-linux-gnu" "x86_64-pc-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64$")
   target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_AARCH64)
-  target_compile_definitions(omptarget.rtl.host PRIVATE
-      LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE="aarch64-unknown-linux-gnu")
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "aarch64-unknown-linux-gnu" "aarch64-unknown-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)
 elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "s390x$")
   target_compile_definitions(omptarget.rtl.host PRIVATE TARGET_ELF_ID=EM_S390)
-  target_compile_definitions(omptarget.rtl.host PRIVATE
-      LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE="s390x-ibm-linux-gnu")
   list(APPEND LIBOMPTARGET_SYSTEM_TARGETS 
        "s390x-ibm-linux-gnu" "s390x-ibm-linux-gnu-LTO")
   set(LIBOMPTARGET_SYSTEM_TARGETS "${LIBOMPTARGET_SYSTEM_TARGETS}" PARENT_SCOPE)

offload/plugins-nextgen/host/src/rtl.cpp

@@ -30,6 +30,17 @@
 #include "llvm/Frontend/OpenMP/OMPGridValues.h"
 #include "llvm/Support/DynamicLibrary.h"
 
+#if !defined(__BYTE_ORDER__) || !defined(__ORDER_LITTLE_ENDIAN__) ||           \
+    !defined(__ORDER_BIG_ENDIAN__)
+#error "Missing preprocessor definitions for endianness detection."
+#endif
+
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+#define LITTLEENDIAN_CPU
+#elif defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
+#define BIGENDIAN_CPU
+#endif
+
 // The number of devices in this plugin.
 #define NUM_DEVICES 4
 
@@ -38,11 +49,6 @@
 #define TARGET_ELF_ID EM_NONE
 #endif
 
-// The target triple should be defined at compile-time by the build system.
-#ifndef LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE
-#define LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE ""
-#endif
-
 namespace llvm {
 namespace omp {
 namespace target {
@@ -421,7 +427,25 @@ struct GenELF64PluginTy final : public GenericPluginTy {
   Expected<bool> isELFCompatible(StringRef) const override { return true; }
 
   Triple::ArchType getTripleArch() const override {
-    return llvm::Triple(LIBOMPTARGET_NEXTGEN_GENERIC_PLUGIN_TRIPLE).getArch();
+#if defined(__x86_64__)
+    return llvm::Triple::x86_64;
+#elif defined(__s390x__)
+    return llvm::Triple::systemz;
+#elif defined(__aarch64__)
+#ifdef LITTLEENDIAN_CPU
+    return llvm::Triple::aarch64_le;
+#else
+    return llvm::Triple::aarch64_be;
+#endif
+#elif defined(__powerpc64__)
+#ifdef LITTLEENDIAN_CPU
+    return llvm::Triple::ppc64le;
+#else
+    return llvm::Triple::ppc64;
+#endif
+#else
+    return llvm::Triple::UnknownArch;
+#endif
   }
 };