Override rustc version in ui and mir-opt tests to get stable hashes

Building a dozen separate regexps for each test in compiletest consumes significant amounts of CPU cycles.
Using `RUSTC_FORCE_INCR_COMP_ARTIFACT_HEADER` stabilizes hashes calcuated for the individual tests so
no test-dependent normalization is needed. Hashes for the standard library still change so some
normalizations are still needed.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index cb1b0ebf8db..176c06114e0 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -1540,6 +1540,9 @@ note: if you're sure you want to do this, please open an issue as to why. In the
             }
         }
         cmd.env("RUSTC_BOOTSTRAP", "1");
+        // Override the rustc version used in symbol hashes to reduce the amount of normalization
+        // needed when diffing test output.
+        cmd.env("RUSTC_FORCE_RUSTC_VERSION", "compiletest");
         cmd.env("DOC_RUST_LANG_ORG_CHANNEL", builder.doc_rust_lang_org_channel());
         builder.add_rust_test_threads(&mut cmd);