Test

.github/workflows/perf.yml

@@ -115,6 +115,9 @@ jobs:
             --host-dmd "$HOST_DMD" \
             --out "$GITHUB_WORKSPACE/results.json"
 
+      - name: Show results
+        run: cat "$GITHUB_WORKSPACE/results.json"
+
       # perf-comment.yml picks this up and posts the comment.
       - name: Upload results
         if: github.event_name == 'pull_request'

compiler/src/dmd/main.d

@@ -178,6 +178,37 @@ private int tryMain(const(char)[][] argv, out Param params)
     Strings libmodules;
     global._init();
 
+    // TESTING ONLY — deliberate busy loop to verify perf bot detects regressions.
+    // Uses ldc.llvmasm optimization barrier so LLVM cannot constant-fold or delete
+    // the loop. Same technique as Google Benchmark's DoNotOptimize.
+    // Remove before merging.
+    {
+        version (LDC)
+        {
+            import ldc.llvmasm;
+            long dummy = 1;
+            foreach (i; 0 .. 500_000)
+            {
+                dummy ^= (dummy << 13);
+                dummy ^= (dummy >>> 7);
+                dummy ^= (dummy << 17);
+                __asm!void("", "r,~{memory}", dummy);
+            }
+        }
+        else
+        {
+            long dummy = 1;
+            foreach (i; 0 .. 500_000)
+            {
+                dummy ^= (dummy << 13);
+                dummy ^= (dummy >>> 7);
+                dummy ^= (dummy << 17);
+            }
+            if (dummy == 0)
+                fputs("", stderr);
+        }
+    }
+
     ErrorSink eSink = global.errorSink;
 
     scope(exit)