Only pass -Zincremental-verify-ich for incremental compiles

Author: xmakro

compiler/rustc_query_impl/src/plumbing.rs

@@ -100,7 +100,18 @@ fn encode_query_values_inner<'a, 'tcx, C, V>(
 }
 
 pub(crate) fn verify_query_key_hashes<'tcx>(tcx: TyCtxt<'tcx>) {
-    if tcx.sess.opts.unstable_opts.incremental_verify_ich || cfg!(debug_assertions) {
+    // Under debug assertions, always check for query key fingerprint collisions.
+    // Fingerprints do not depend on whether a dep graph exists, so a collision
+    // found in a non-incremental build means incremental compilation of the same
+    // code would misbehave — the broad non-incremental test coverage is valuable.
+    //
+    // `-Zincremental-verify-ich`, however, asks to verify incremental compilation
+    // hashes: without a dep graph there is nothing to verify, and the sweep would
+    // only waste time. This matters because rustc-perf passes the flag on every
+    // compile, including non-incremental benchmark runs.
+    if cfg!(debug_assertions)
+        || (tcx.sess.opts.unstable_opts.incremental_verify_ich && tcx.dep_graph.is_fully_enabled())
+    {
         tcx.sess.time("verify_query_key_hashes", || {
             for_each_query_vtable!(ALL, tcx, |query| {
                 verify_query_key_hashes_inner(query, tcx);