From 1b9d519e4520319f92d67a79a7e4815bc9c384a5 Mon Sep 17 00:00:00 2001
From: Andreas Beckmann <anbe@debian.org>
Date: Wed, 16 Jan 2019 21:37:17 +0000
Subject: [PATCH] [PATCH 2/2] perform compile test to select -march or -mcpu
 for clang

Gbp-Pq: Name find-clang-march-mcpu-flag.patch
---
 cmake/LLVM.cmake | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/cmake/LLVM.cmake b/cmake/LLVM.cmake
index 16edc2b..3b511a0 100644
--- a/cmake/LLVM.cmake
+++ b/cmake/LLVM.cmake
@@ -502,15 +502,6 @@ if(NOT DEFINED LINK_WITH_CLANG)
 
 endif()
 
-####################################################################
-#X86 has -march and -mcpu reversed, for clang
-
-if(CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "(powerpc|armv7|aarch64)")
-  set(CLANG_MARCH_FLAG "-mcpu=")
-else()
-  set(CLANG_MARCH_FLAG "-march=")
-endif()
-
 ####################################################################
 
 macro(CHECK_ALIGNOF TYPE TYPEDEF OUT_VAR)
@@ -715,6 +706,26 @@ else()
 endif()
 
 
+####################################################################
+# Some architectures have -march and -mcpu reversed
+
+if(NOT DEFINED ${CLANG_MARCH_FLAG})
+  message(STATUS "Checking clang -march vs. -mcpu flag")
+  custom_try_compile_clang_silent("" "return 0;" RES ${CLANG_TARGET_OPTION}${LLC_TRIPLE} -march=${LLC_HOST_CPU})
+  if(NOT RES)
+    set(CLANG_MARCH_FLAG "-march=")
+  else()
+    custom_try_compile_clang_silent("" "return 0;" RES ${CLANG_TARGET_OPTION}${LLC_TRIPLE} -mcpu=${LLC_HOST_CPU})
+    if(NOT RES)
+      set(CLANG_MARCH_FLAG "-mcpu=")
+    else()
+      message(FATAL_ERROR "Could not determine whether to use -march or -mcpu with clang")
+    endif()
+  endif()
+
+  set(CLANG_MARCH_FLAG ${CLANG_MARCH_FLAG} CACHE INTERNAL "Clang option used to specify the target cpu")
+endif()
+
 ####################################################################
 
 # This tests that we can actually link to the llvm libraries.
-- 
2.30.2