[PATCH] D88584: [gn build] Support building with ThinLTO

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks created this revision.
aeubanks added reviewers: thakis, hans, rnk.
Herald added subscribers: llvm-commits, dexonsmith, inglorion.
Herald added a project: LLVM.
aeubanks requested review of this revision.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D88584

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


Index: llvm/utils/gn/build/buildflags.gni
===================================================================
--- llvm/utils/gn/build/buildflags.gni
+++ llvm/utils/gn/build/buildflags.gni
@@ -10,16 +10,22 @@
 
   # 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
 }
Index: llvm/utils/gn/build/BUILD.gn
===================================================================
--- llvm/utils/gn/build/BUILD.gn
+++ llvm/utils/gn/build/BUILD.gn
@@ -256,6 +256,27 @@
     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") {


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