Disable sign extension in SignExtLowering.cpp (#5676)

* Disable sign extension in SignExtLowering.cpp

The sign extension lowering pass would previously lower away the sign extension
instructions, but it wouldn't disable the sign extension feature, so follow-on
passes such as optimize-instructions could reintroduce sign extension
instructions.

Fix the pass to disable the sign extension feature to prevent sign extension
instructions from being reintroduced later.

* update pass description

1 files changed, 8 insertions, 0 deletions

diff --git a/src/passes/SignExtLowering.cpp b/src/passes/SignExtLowering.cpp
index 7d03046ea..beb36494f 100644
--- a/src/passes/SignExtLowering.cpp
+++ b/src/passes/SignExtLowering.cpp
@@ -68,6 +68,14 @@ struct SignExtLowering : public WalkerPass<PostWalker<SignExtLowering>> {
       }
     }
   }
+
+  void run(Module* module) override {
+    if (!module->features.has(FeatureSet::SignExt)) {
+      return;
+    }
+    super::run(module);
+    module->features.disable(FeatureSet::SignExt);
+  }
 };
 
 Pass* createSignExtLoweringPass() { return new SignExtLowering(); }