From c06b3762a09e95443fd0f159b2675209db1dbb29 Mon Sep 17 00:00:00 2001
From: "Alon Zakai (kripken)" <alonzakai@gmail.com>
Date: Sat, 11 Feb 2017 21:55:14 -0800
Subject: optimize out a sign-ext into a store of the same size

---
 src/passes/OptimizeInstructions.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

(limited to 'src/passes/OptimizeInstructions.cpp')

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 1c549cab6..cf5ad982e 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -525,6 +525,12 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions,
               }
             }
           }
+        } else if (auto* ext = getSignExt(binary)) {
+          // if sign extending the exact bit size we store, we can skip the extension
+          // if extending something bigger, then we just alter bits we don't save anyhow
+          if (getSignExtBits(binary) >= store->bytes * 8) {
+            store->value = ext;
+          }
         }
       } else if (auto* unary = store->value->dynCast<Unary>()) {
         if (unary->op == WrapInt64) {
-- 
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