From 8013548bbb74f10577ea429f5a9c6f1dcfa6bd64 Mon Sep 17 00:00:00 2001
From: Lioncash <mathew1800@gmail.com>
Date: Sat, 29 Sep 2018 03:57:16 -0400
Subject: [PATCH] constant_propagation_pass: Fold OR operations

---
 src/ir_opt/constant_propagation_pass.cpp | 32 ++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/src/ir_opt/constant_propagation_pass.cpp b/src/ir_opt/constant_propagation_pass.cpp
index edcea826..f315a3f1 100644
--- a/src/ir_opt/constant_propagation_pass.cpp
+++ b/src/ir_opt/constant_propagation_pass.cpp
@@ -76,6 +76,34 @@ void FoldEOR(IR::Inst& inst, bool is_32_bit) {
         inst.ReplaceUsesWith(lhs);
     }
 }
+
+// Folds OR operations based on the following:
+//
+// 1. imm_x | imm_y -> result
+// 2. x | 0 -> x
+// 3. 0 | y -> y
+//
+void FoldOR(IR::Inst& inst, bool is_32_bit) {
+    const auto lhs = inst.GetArg(0);
+    const auto rhs = inst.GetArg(1);
+
+    const bool is_lhs_immediate = lhs.IsImmediate();
+    const bool is_rhs_immediate = rhs.IsImmediate();
+
+    if (is_lhs_immediate && is_rhs_immediate) {
+        const u64 result = lhs.GetImmediateAsU64() | rhs.GetImmediateAsU64();
+
+        if (is_32_bit) {
+            inst.ReplaceUsesWith(IR::Value{static_cast<u32>(result)});
+        } else {
+            inst.ReplaceUsesWith(IR::Value{result});
+        }
+    } else if (is_lhs_immediate && lhs.GetImmediateAsU64() == 0) {
+        inst.ReplaceUsesWith(rhs);
+    } else if (is_rhs_immediate && rhs.GetImmediateAsU64() == 0) {
+        inst.ReplaceUsesWith(lhs);
+    }
+}
 } // Anonymous namespace
 
 void ConstantPropagation(IR::Block& block) {
@@ -109,6 +137,10 @@ void ConstantPropagation(IR::Block& block) {
         case IR::Opcode::Eor64:
             FoldEOR(inst, opcode == IR::Opcode::Eor32);
             break;
+        case IR::Opcode::Or32:
+        case IR::Opcode::Or64:
+            FoldOR(inst, opcode == IR::Opcode::Or32);
+            break;
         case IR::Opcode::ZeroExtendByteToWord: {
             if (!inst.AreAllArgsImmediates())
                 break;