From e473d40832ab3caa14151285cab724b76ab0706e Mon Sep 17 00:00:00 2001
From: Joel Linn <jl@conductive.de>
Date: Wed, 4 Nov 2020 20:01:24 +0100
Subject: [PATCH] clang Use `llvm-ar` linker when LTO flag is set. It is
 required for some clang features like `-flto`. Still defaults to `ar` if the
 `LinkTimeOptimization` flag is not set.

---
 modules/gmake/tests/cpp/test_clang.lua | 17 +++++++++++++++++
 src/tools/clang.lua                    |  8 ++++++--
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/modules/gmake/tests/cpp/test_clang.lua b/modules/gmake/tests/cpp/test_clang.lua
index f8cb1e0dbf..2e60290563 100644
--- a/modules/gmake/tests/cpp/test_clang.lua
+++ b/modules/gmake/tests/cpp/test_clang.lua
@@ -44,3 +44,20 @@ ifeq ($(config),debug)
 		]]
 	end
 
+	function suite.usesCorrectCompilersAndLinkTimeOptimization()
+		flags { "LinkTimeOptimization" }
+		make.cppConfigs(prj)
+		test.capture [[
+ifeq ($(config),debug)
+  ifeq ($(origin CC), default)
+    CC = clang
+  endif
+  ifeq ($(origin CXX), default)
+    CXX = clang++
+  endif
+  ifeq ($(origin AR), default)
+    AR = llvm-ar
+  endif
+		]]
+	end
+
diff --git a/src/tools/clang.lua b/src/tools/clang.lua
index 7460a0a192..1da61dfbb0 100644
--- a/src/tools/clang.lua
+++ b/src/tools/clang.lua
@@ -324,9 +324,13 @@
 	clang.tools = {
 		cc = "clang",
 		cxx = "clang++",
-		ar = "ar"
+		ar = function(cfg) return iif(cfg.flags.LinkTimeOptimization, "llvm-ar", "ar") end
 	}
 
 	function clang.gettoolname(cfg, tool)
-		return clang.tools[tool]
+		local value = clang.tools[tool]
+		if type(value) == "function" then
+			value = value(cfg)
+		end
+		return value
 	end