Movability.

2 files changed, 29 insertions, 0 deletions

diff --git a/libevmasm/SemanticInformation.cpp b/libevmasm/SemanticInformation.cpp
index 61a6ccda..4c2290c4 100644
--- a/libevmasm/SemanticInformation.cpp
+++ b/libevmasm/SemanticInformation.cpp
@@ -153,6 +153,31 @@ bool SemanticInformation::isDeterministic(AssemblyItem const& _item)
 	}
 }
 
+bool SemanticInformation::movable(Instruction _instruction)
+{
+	// These are not really functional.
+	if (isDupInstruction(_instruction) || isSwapInstruction(_instruction))
+		return false;
+	InstructionInfo info = instructionInfo(_instruction);
+	if (info.sideEffects)
+		return false;
+	switch (_instruction)
+	{
+	case Instruction::KECCAK256:
+	case Instruction::BALANCE:
+	case Instruction::EXTCODESIZE:
+	case Instruction::RETURNDATASIZE:
+	case Instruction::SLOAD:
+	case Instruction::PC:
+	case Instruction::MSIZE:
+	case Instruction::GAS:
+		return false;
+	default:
+		return true;
+	}
+	return true;
+}
+
 bool SemanticInformation::invalidatesMemory(Instruction _instruction)
 {
 	switch (_instruction)
diff --git a/libevmasm/SemanticInformation.h b/libevmasm/SemanticInformation.h
index e5ea7c18..83656252 100644
--- a/libevmasm/SemanticInformation.h
+++ b/libevmasm/SemanticInformation.h
@@ -49,6 +49,10 @@ struct SemanticInformation
 	/// @returns false if the value put on the stack by _item depends on anything else than
 	/// the information in the current block header, memory, storage or stack.
 	static bool isDeterministic(AssemblyItem const& _item);
+	/// @returns true if the instruction can be moved or copied (together with its arguments)
+	/// without altering the semantics. This means it cannot depend on storage or memory,
+	/// cannot have any side-effects, but it can depend on a call-constant state of the blockchain.
+	static bool movable(solidity::Instruction _instruction);
 	/// @returns true if the given instruction modifies memory.
 	static bool invalidatesMemory(solidity::Instruction _instruction);
 	/// @returns true if the given instruction modifies storage (even indirectly).