bootstrap: update and enable the LLVM version-check

While the `config.toml.example` comments say "we automatically check the
version by default," we actually didn't.  That check was badly out of
date, only allowing 3.5, 3.6, or 3.7.  This it now updated to the new
3.9 minimum requirement, and truly enabled by default.

2 files changed, 8 insertions, 4 deletions

diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 69e0f58f1cd..d6c83e3acfc 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -299,6 +299,7 @@ impl Config {
         let mut config = Config::default();
         config.llvm_enabled = true;
         config.llvm_optimize = true;
+        config.llvm_version_check = true;
         config.use_jemalloc = true;
         config.backtrace = true;
         config.rust_optimize = true;
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 941ea96bbec..c37b1dad4c6 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -259,11 +259,14 @@ fn check_llvm_version(build: &Build, llvm_config: &Path) {
 
     let mut cmd = Command::new(llvm_config);
     let version = output(cmd.arg("--version"));
-    if version.starts_with("3.5") || version.starts_with("3.6") ||
-       version.starts_with("3.7") {
-        return
+    let mut parts = version.split('.').take(2)
+        .filter_map(|s| s.parse::<u32>().ok());
+    if let (Some(major), Some(minor)) = (parts.next(), parts.next()) {
+        if major > 3 || (major == 3 && minor >= 9) {
+            return
+        }
     }
-    panic!("\n\nbad LLVM version: {}, need >=3.5\n\n", version)
+    panic!("\n\nbad LLVM version: {}, need >=3.9\n\n", version)
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]