fix: mark memory module as effectful

This commit fixes a corner-case, where a memory module itself is not
effectful, but it is connected to an effectful *ext* memory module. If
we simply mark all memory modules as pure, this would optimize out the
ext memory module, causing inconsistencies in the sifive -repl-seq-mem
flow. The previous firrtl transforms and hierarchies would be generated
correct, yet the final _ext sram would be omitted completely.

Signed-off-by: Tianrui Wei <tianruiwei@eecs.berkeley.edu>

Author: tianrui-wei

lib/Dialect/FIRRTL/Transforms/LayerSink.cpp

@@ -138,9 +138,9 @@ class EffectInfo {
     // Regular modules may be pure.
     if (auto m = dyn_cast<FModuleOp>(op))
       return update(m);
-    // Memory modules are pure.
-    if (auto m = dyn_cast<FMemModuleOp>(op))
-      return;
+//    // Memory modules are pure.
+//    if (auto m = dyn_cast<FMemModuleOp>(op))
+//      return;
     // All other kinds of modules are effectful.
     // intmodules, extmodules, classes.
     return markEffectful(moduleOp);