diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 3f30756a568ce..2ea026244034f 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -186,7 +186,7 @@ impl Step for Llvm {
         }
 
         // http://llvm.org/docs/HowToCrossCompileLLVM.html
-        if target != build.build {
+        if target != build.build && !emscripten {
             builder.ensure(Llvm {
                 target: build.build,
                 emscripten: false,
diff --git a/src/ci/docker/dist-i686-freebsd/Dockerfile b/src/ci/docker/dist-i686-freebsd/Dockerfile
index 686afc97289b1..673fa4c0c4bc0 100644
--- a/src/ci/docker/dist-i686-freebsd/Dockerfile
+++ b/src/ci/docker/dist-i686-freebsd/Dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:16.04
+FROM ubuntu:18.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
   clang \
diff --git a/src/dlmalloc b/src/dlmalloc
index d3812c3accaee..a2b424b600235 160000
--- a/src/dlmalloc
+++ b/src/dlmalloc
@@ -1 +1 @@
-Subproject commit d3812c3accaee7ad23068ed4fc089cc05c7a538f
+Subproject commit a2b424b600235af58f453577c2da1b0e1de2ffa5
diff --git a/src/libcompiler_builtins b/src/libcompiler_builtins
index 0a95675bab808..345447948f7a5 160000
--- a/src/libcompiler_builtins
+++ b/src/libcompiler_builtins
@@ -1 +1 @@
-Subproject commit 0a95675bab808c49f86208bacc89c5d9c53ac43f
+Subproject commit 345447948f7a51eca970fa036cefd613d54a4f79
diff --git a/src/librustc_resolve/resolve_imports.rs b/src/librustc_resolve/resolve_imports.rs
index 07b08e2e61ac0..95a507ab9e351 100644
--- a/src/librustc_resolve/resolve_imports.rs
+++ b/src/librustc_resolve/resolve_imports.rs
@@ -1026,9 +1026,12 @@ fn import_path_to_string(names: &[SpannedIdent],
         if names.is_empty() {
             import_directive_subclass_to_string(subclass)
         } else {
-            (format!("{}::{}",
+            let x = format!("{}::{}",
                      names_to_string(names),
-                     import_directive_subclass_to_string(subclass)))
+                     import_directive_subclass_to_string(subclass));
+            assert!(!names.is_empty());
+            assert!(!x.starts_with("::"));
+            return x
         }
     }
 }
diff --git a/src/llvm b/src/llvm
index bc344d5bc23c6..9f81beaf32608 160000
--- a/src/llvm
+++ b/src/llvm
@@ -1 +1 @@
-Subproject commit bc344d5bc23c61ff9baf82d268a0edf199933cc3
+Subproject commit 9f81beaf32608fbe1fe0f2a82f974e800e9d8c62
diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index 611d63f6a4d14..4dfc4029d75dc 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -552,9 +552,11 @@ static unsigned fromRust(LLVMRustDIFlags Flags) {
   if (isSet(Flags & LLVMRustDIFlags::FlagRValueReference)) {
     Result |= DINode::DIFlags::FlagRValueReference;
   }
+#if LLVM_VERSION_LE(4, 0)
   if (isSet(Flags & LLVMRustDIFlags::FlagExternalTypeRef)) {
     Result |= DINode::DIFlags::FlagExternalTypeRef;
   }
+#endif
   if (isSet(Flags & LLVMRustDIFlags::FlagIntroducedVirtual)) {
     Result |= DINode::DIFlags::FlagIntroducedVirtual;
   }
diff --git a/src/rustllvm/llvm-rebuild-trigger b/src/rustllvm/llvm-rebuild-trigger
index 2635ca73303e7..3cd044708cee2 100644
--- a/src/rustllvm/llvm-rebuild-trigger
+++ b/src/rustllvm/llvm-rebuild-trigger
@@ -1,4 +1,4 @@
 # If this file is modified, then llvm will be (optionally) cleaned and then rebuilt.
 # The actual contents of this file do not matter, but to trigger a change on the
 # build bots then the contents should be changed so git updates the mtime.
-2018-01-25
+2018-02-09
diff --git a/src/test/run-pass/backtrace-debuginfo.rs b/src/test/run-pass/backtrace-debuginfo.rs
index e8b5f3490e50e..2b82a8943636e 100644
--- a/src/test/run-pass/backtrace-debuginfo.rs
+++ b/src/test/run-pass/backtrace-debuginfo.rs
@@ -15,11 +15,14 @@
 // Unfortunately, LLVM has no "disable" option for this, so we have to set
 // "enable" to 0 instead.
 
-// compile-flags:-g -Cllvm-args=-enable-tail-merge=0
+// compile-flags:-g -Cllvm-args=-enable-tail-merge=0 -Cllvm-args=-opt-bisect-limit=0
 // ignore-pretty issue #37195
 // ignore-cloudabi spawning processes is not supported
 // ignore-emscripten spawning processes is not supported
 
+// note that above `-opt-bisect-limit=0` is used to basically disable
+// optimizations
+
 use std::env;
 
 #[path = "backtrace-debuginfo-aux.rs"] mod aux;
@@ -114,18 +117,26 @@ fn outer(mut counter: i32, main_pos: Pos) {
     inner_inlined(&mut counter, main_pos, pos!());
 }
 
-fn check_trace(output: &str, error: &str) {
+fn check_trace(output: &str, error: &str) -> Result<(), String> {
     // reverse the position list so we can start with the last item (which was the first line)
     let mut remaining: Vec<&str> = output.lines().map(|s| s.trim()).rev().collect();
 
-    assert!(error.contains("stack backtrace"), "no backtrace in the error: {}", error);
+    if !error.contains("stack backtrace") {
+        return Err(format!("no backtrace found in stderr:\n{}", error))
+    }
     for line in error.lines() {
         if !remaining.is_empty() && line.contains(remaining.last().unwrap()) {
             remaining.pop();
         }
     }
-    assert!(remaining.is_empty(),
-            "trace does not match position list: {}\n---\n{}", error, output);
+    if !remaining.is_empty() {
+        return Err(format!("trace does not match position list\n\
+            still need to find {:?}\n\n\
+            --- stdout\n{}\n\
+            --- stderr\n{}",
+            remaining, output, error))
+    }
+    Ok(())
 }
 
 fn run_test(me: &str) {
@@ -133,6 +144,7 @@ fn run_test(me: &str) {
     use std::process::Command;
 
     let mut i = 0;
+    let mut errors = Vec::new();
     loop {
         let out = Command::new(me)
                           .env("RUST_BACKTRACE", "full")
@@ -143,10 +155,20 @@ fn run_test(me: &str) {
             assert!(output.contains("done."), "bad output for successful run: {}", output);
             break;
         } else {
-            check_trace(output, error);
+            if let Err(e) = check_trace(output, error) {
+                errors.push(e);
+            }
         }
         i += 1;
     }
+    if errors.len() > 0 {
+        for error in errors {
+            println!("---------------------------------------");
+            println!("{}", error);
+        }
+
+        panic!("found some errors");
+    }
 }
 
 #[inline(never)]