From 82d82f1a4e9aa1ce1b80acbab4a95262ec7782ae Mon Sep 17 00:00:00 2001
From: Max Graey <maxgraey@gmail.com>
Date: Tue, 7 Jun 2022 21:34:23 +0300
Subject: [Optimize Instructions] Simplify sign extentions (Part 2) (#4382)

Similar to #4004 but for 32-bit integers

i32(x) << 24 >> 24   ==>   i32.extend8_s(x)
i32(x) << 16 >> 16   ==>   i32.extend16_s(x)
---
 src/passes/OptimizeInstructions.cpp | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

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

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index c4a5b2ed4..c4ce8c239 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -476,6 +476,22 @@ struct OptimizeInstructions
                 break;
             }
           }
+          // i32(x) << 24 >> 24   ==>   i32.extend8_s(x)
+          // i32(x) << 16 >> 16   ==>   i32.extend16_s(x)
+          if (matches(curr,
+                      binary(ShrSInt32,
+                             binary(ShlInt32, any(&x), i32(&c1)),
+                             i32(&c2))) &&
+              Bits::getEffectiveShifts(c1) == Bits::getEffectiveShifts(c2)) {
+            switch (32 - Bits::getEffectiveShifts(c1)) {
+              case 8:
+                return replaceCurrent(builder.makeUnary(ExtendS8Int32, x));
+              case 16:
+                return replaceCurrent(builder.makeUnary(ExtendS16Int32, x));
+              default:
+                break;
+            }
+          }
         }
       }
       {
-- 
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