From 2da2cf9058027039774f39ea9fb7cc2b4dabffa2 Mon Sep 17 00:00:00 2001
From: Lioncash <mathew1800@gmail.com>
Date: Fri, 5 Oct 2018 18:08:16 -0400
Subject: [PATCH] constant_propagation_pass: Fold SignExtend{Type}ToWord
 opcodes if possible

---
 src/ir_opt/constant_propagation_pass.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/ir_opt/constant_propagation_pass.cpp b/src/ir_opt/constant_propagation_pass.cpp
index 037f522e..10f1d720 100644
--- a/src/ir_opt/constant_propagation_pass.cpp
+++ b/src/ir_opt/constant_propagation_pass.cpp
@@ -114,6 +114,15 @@ void FoldOR(IR::Inst& inst, bool is_32_bit) {
     }
 }
 
+void FoldSignExtendXToWord(IR::Inst& inst) {
+    if (!inst.AreAllArgsImmediates()) {
+        return;
+    }
+
+    const s64 value = inst.GetArg(0).GetImmediateAsS64();
+    inst.ReplaceUsesWith(IR::Value{static_cast<u32>(value)});
+}
+
 void FoldZeroExtendXToWord(IR::Inst& inst) {
     if (!inst.AreAllArgsImmediates()) {
         return;
@@ -172,6 +181,10 @@ void ConstantPropagation(IR::Block& block) {
         case IR::Opcode::Not64:
             FoldNOT(inst, opcode == IR::Opcode::Not32);
             break;
+        case IR::Opcode::SignExtendByteToWord:
+        case IR::Opcode::SignExtendHalfToWord:
+            FoldSignExtendXToWord(inst);
+            break;
         case IR::Opcode::ZeroExtendByteToWord:
         case IR::Opcode::ZeroExtendHalfToWord:
             FoldZeroExtendXToWord(inst);