From eeb7348dc3fbb0b85a7f45b5972e744085cb632d Mon Sep 17 00:00:00 2001
From: Michael Woerister <michaelwoerister@posteo>
Date: Wed, 22 May 2019 13:00:09 +0200
Subject: [PATCH] PGO: Check that pgo-use file actually exists. LLVM seems to
 only emit an easy-to-overlook warning otherwise.

---
 src/librustc/session/mod.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 4d47491661e..3d8092f6e00 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -1272,6 +1272,15 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         sess.err("Linker plugin based LTO is not supported together with \
                   `-C prefer-dynamic` when targeting MSVC");
     }
+
+    // Make sure that any given profiling data actually exists so LLVM can't
+    // decide to silently skip PGO.
+    if let Some(ref path) = sess.opts.debugging_opts.pgo_use {
+        if !path.exists() {
+            sess.err(&format!("File `{}` passed to `-Zpgo-use` does not exist.",
+                              path.display()));
+        }
+    }
 }
 
 /// Hash value constructed out of all the `-C metadata` arguments passed to the