From 9640cfd77eec32f7b173a5dafbeac510d4b57253 Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Fri, 27 Nov 2020 22:26:06 +0000
Subject: [PATCH] [ewasm] Add i32.select/i64.select

---
 Changelog.md                                       |  1 +
 libyul/backends/wasm/BinaryTransform.cpp           |  2 ++
 libyul/backends/wasm/WasmDialect.cpp               |  4 ++++
 .../yulInterpreter/EwasmBuiltinInterpreter.cpp     | 14 ++++++++++++++
 4 files changed, 21 insertions(+)

diff --git a/Changelog.md b/Changelog.md
index 0851a79d2..7838a1487 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -4,6 +4,7 @@ Language Features:
  * Code generator: Support copying dynamically encoded structs from calldata to memory.
  * Code generator: Support copying of nested arrays from calldata to memory.
  * The fallback function can now also have a single ``calldata`` argument (equaling ``msg.data``) and return ``bytes memory`` (which will not be ABI-encoded but returned as-is).
+ * Wasm backend: Add ``i32.select`` and ``i64.select`` instructions.
 
 Compiler Features:
  * Code Generator: Avoid memory allocation for default value if it is not used.
diff --git a/libyul/backends/wasm/BinaryTransform.cpp b/libyul/backends/wasm/BinaryTransform.cpp
index a36742750..df700527e 100644
--- a/libyul/backends/wasm/BinaryTransform.cpp
+++ b/libyul/backends/wasm/BinaryTransform.cpp
@@ -156,6 +156,8 @@ Opcode constOpcodeFor(ValueType _type)
 }
 
 static map<string, uint8_t> const builtins = {
+	{"i32.select", 0x1b},
+	{"i64.select", 0x1b},
 	{"i32.load", 0x28},
 	{"i64.load", 0x29},
 	{"i32.load8_s", 0x2c},
diff --git a/libyul/backends/wasm/WasmDialect.cpp b/libyul/backends/wasm/WasmDialect.cpp
index 1c7755d6a..1e77e1d47 100644
--- a/libyul/backends/wasm/WasmDialect.cpp
+++ b/libyul/backends/wasm/WasmDialect.cpp
@@ -120,6 +120,10 @@ WasmDialect::WasmDialect()
 	addFunction("i32.drop", {i32}, {});
 	addFunction("i64.drop", {i64}, {});
 
+	// Select is also overloaded.
+	addFunction("i32.select", {i32, i32, i32}, {i32});
+	addFunction("i64.select", {i64, i64, i32}, {i64});
+
 	addFunction("nop", {}, {});
 	addFunction("unreachable", {}, {}, false);
 	m_functions["unreachable"_yulstring].sideEffects.storage = SideEffects::None;
diff --git a/test/tools/yulInterpreter/EwasmBuiltinInterpreter.cpp b/test/tools/yulInterpreter/EwasmBuiltinInterpreter.cpp
index 10c8af230..7d50e1527 100644
--- a/test/tools/yulInterpreter/EwasmBuiltinInterpreter.cpp
+++ b/test/tools/yulInterpreter/EwasmBuiltinInterpreter.cpp
@@ -154,6 +154,20 @@ u256 EwasmBuiltinInterpreter::evalBuiltin(
 	}
 	else if (fun == "i32.drop" || fun == "i64.drop" || fun == "nop")
 		return {};
+	else if (fun == "i32.select")
+	{
+		if ((arg.at(2) & 0xffffffff) == 0)
+			return arg.at(1);
+		else
+			return arg.at(0);
+	}
+	else if (fun == "i64.select")
+	{
+		if ((arg.at(2) & 0xffffffffffffffff) == 0)
+			return arg.at(1);
+		else
+			return arg.at(0);
+	}
 	else if (fun == "i32.wrap_i64")
 		return arg.at(0) & uint32_t(-1);
 	else if (fun == "i64.extend_i32_u")