# HG changeset patch
# User David Major <dmajor@mozilla.com>
# Date 1531758396 14400
# Node ID a2ae515ee43f5561ab77875d21738a8c8d53999e
# Parent  444db96136e5c76738fbae53a1ec4ac3b985d886
Bug 1448980: Make --enable-lto work with clang-cl. r=froydnj

diff --git a/build/moz.configure/toolchain.configure b/build/moz.configure/toolchain.configure
--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -1570,37 +1570,45 @@ js_option('--enable-lto',
           help='Enable LTO')
 
 
 @depends('--enable-lto', c_compiler)
 @imports('multiprocessing')
 def lto(value, c_compiler):
     cflags = []
     ldflags = []
-
-    # clang and clang-cl
-    if c_compiler.type in ('clang', 'clang-cl'):
-        if len(value) and value[0].lower() == 'full':
+    enabled = None
+
+    if value:
+        enabled = True
+        if c_compiler.type == 'clang':
+            if len(value) and value[0].lower() == 'full':
+                cflags.append("-flto")
+                ldflags.append("-flto")
+            else:
+                cflags.append("-flto=thin")
+                ldflags.append("-flto=thin")
+        elif c_compiler.type == 'clang-cl':
+            if len(value) and value[0].lower() == 'full':
+                cflags.append("-flto")
+            else:
+                cflags.append("-flto=thin")
+            # With clang-cl, -flto can only be used with -c or -fuse-ld=lld.
+            # AC_TRY_LINKs during configure don't have -c, so pass -fuse-ld=lld.
+            cflags.append("-fuse-ld=lld");
+        else:
+            num_cores = multiprocessing.cpu_count()
             cflags.append("-flto")
-            ldflags.append("-flto")
-        elif value:
-            cflags.append("-flto=thin")
-            ldflags.append("-flto=thin")
-
-    # gcc and other compilers
-    elif value:
-        num_cores = multiprocessing.cpu_count()
-        cflags.append("-flto")
-        cflags.append("-flifetime-dse=1")
-
-        ldflags.append("-flto=%s" % num_cores)
-        ldflags.append("-flifetime-dse=1")
+            cflags.append("-flifetime-dse=1")
+
+            ldflags.append("-flto=%s" % num_cores)
+            ldflags.append("-flifetime-dse=1")
 
     return namespace(
-        enabled="1" if value else None,
+        enabled=enabled,
         cflags=cflags,
         ldflags=ldflags
     )
 
 
 add_old_configure_assignment('MOZ_LTO', lto.enabled)
 set_config('MOZ_LTO', lto.enabled)
 set_define('MOZ_LTO', lto.enabled)