[llvm] b29573b - [gn build] Support building with ThinLTO

[Arthur Eubanks via llvm-commits]

Author: Arthur Eubanks
Date: 2020-10-01T13:48:31-07:00
New Revision: b29573b672d795dfc58aaf70c70511229584e3c3

URL: https://github.com/llvm/llvm-project/commit/b29573b672d795dfc58aaf70c70511229584e3c3
DIFF: https://github.com/llvm/llvm-project/commit/b29573b672d795dfc58aaf70c70511229584e3c3.diff

LOG: [gn build] Support building with ThinLTO

Differential Revision: https://reviews.llvm.org/D88584

Added: 
    

Modified: 
    llvm/utils/gn/build/BUILD.gn
    llvm/utils/gn/build/buildflags.gni

Removed: 
    


################################################################################
diff  --git a/llvm/utils/gn/build/BUILD.gn b/llvm/utils/gn/build/BUILD.gn
index 373d371f017b..f88f4bcc4b6b 100644
--- a/llvm/utils/gn/build/BUILD.gn
+++ b/llvm/utils/gn/build/BUILD.gn
@@ -256,6 +256,27 @@ config("compiler_defaults") {
     cflags += [ "-fsanitize=thread" ]
     ldflags += [ "-fsanitize=thread" ]
   }
+
+  if (use_thinlto) {
+    assert(is_clang, "ThinLTO only supported on Clang")
+
+    lto_opt_level = 2
+
+    cflags += [ "-flto=thin" ]
+
+    if (host_os == "win") {
+      ldflags += [
+        "/opt:lldlto=" + lto_opt_level,
+        "/opt:lldltojobs=" + max_jobs_per_lto_link,
+      ]
+    } else {
+      ldflags += [
+        "-flto=thin",
+        "-Wl,--thinlto-jobs=" + max_jobs_per_lto_link,
+        "-Wl,--lto-O" + lto_opt_level,
+      ]
+    }
+  }
 }
 
 config("no_exceptions") {

diff  --git a/llvm/utils/gn/build/buildflags.gni b/llvm/utils/gn/build/buildflags.gni
index b04eae19a784..9ad494a3c1e9 100644
--- a/llvm/utils/gn/build/buildflags.gni
+++ b/llvm/utils/gn/build/buildflags.gni
@@ -10,16 +10,22 @@ declare_args() {
 
   # Whether to build with asan.
   use_asan = false
-}
-
-# args that depend on other args must live in a later declare_args() block.
-declare_args() {
-  # Whether to build with optimizations.
-  is_optimized = !is_debug
 
   # Whether to enable assertions.
   llvm_enable_assertions = true
 
   # Whether to enable expensive checks.
   llvm_enable_expensive_checks = false
+
+  # Whether to build with ThinLTO.
+  use_thinlto = false
+
+  # Max jobs per ThinLTO link.
+  max_jobs_per_lto_link = 8
+}
+
+# args that depend on other args must live in a later declare_args() block.
+declare_args() {
+  # Whether to build with optimizations.
+  is_optimized = !is_debug
 }