mir-opts.diff

diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 5bc4d164265..211d45e022e 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1939,6 +1939,17 @@ fn make_compile_args(
         // Use a single thread for efficiency and a deterministic error message order
         rustc.arg("-Zthreads=1");
 
+        // Hide libstd sources from ui tests to make sure we generate the stderr
+        // output that users will see.
+        // Without this, we may be producing good diagnostics in-tree but users
+        // will not see half the information.
+        //
+        // This also has the benefit of more effectively normalizing output between different
+        // compilers, so that we don't have to know the `/rustc/$sha` output to normalize after the
+        // fact.
+        rustc.arg("-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX");
+        rustc.arg("-Ztranslate-remapped-path-to-local-path=no");
+
         // Optionally prevent default --sysroot if specified in test compile-flags.
         if !self.props.compile_flags.iter().any(|flag| flag.starts_with("--sysroot")) {
             // In stage 0, make sure we use `stage0-sysroot` instead of the bootstrap sysroot.
@@ -2014,13 +2025,6 @@ fn make_compile_args(
                 rustc.arg("-Ccodegen-units=1");
                 // Hide line numbers to reduce churn
                 rustc.arg("-Zui-testing");
-                // Hide libstd sources from ui tests to make sure we generate the stderr
-                // output that users will see.
-                // Without this, we may be producing good diagnostics in-tree but users
-                // will not see half the information.
-                rustc.arg("-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX");
-                rustc.arg("-Ztranslate-remapped-path-to-local-path=no");
-
                 rustc.arg("-Zdeduplicate-diagnostics=no");
                 // FIXME: use this for other modes too, for perf?
                 rustc.arg("-Cstrip=debuginfo");