Prevent miscompilation in trivial loop {}

Ideally, we would want to handle a broader set of cases to fully fix the
underlying bug here. That is currently relatively expensive at compile and
runtime, so we don't do that for now.

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -153,7 +153,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         bx.set_personality_fn(cx.eh_personality());
     }
 
-    bx.sideeffect();
+    bx.sideeffect(false);
 
     let cleanup_kinds = analyze::cleanup_kinds(&mir);
     // Allocate a `Block` for every basic block, except