[emulator] Mask arithmetic operands consistently up front

The basic two-operand arithmetic cases masked operands only when recording the
flag context, while evaluating the operation on the raw operands, and the
double-precision cases mask to sz/2 for unrelated reasons. This was noted as
confusing in review. Mask both operands to sz once at the top of each case and
use those masked values for both the computation and m_lastArithmetic, and add
a comment explaining why the double-precision ops mask differently. No behavior
change.

Addresses bdash review comment on PR #8314.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: xusheng6

plugins/emulator/core/llilemulator.cpp

@@ -977,58 +977,62 @@ intx::uint512 LLILEmulator::EvalExpr(const LowLevelILInstruction& expr)
 	}
 
 	// --- Two-operand arithmetic ---
+	// Convention: operands are masked to the operation size `sz` up front, and the same
+	// masked values are used both for the computation and for the flag context recorded in
+	// m_lastArithmetic. (Double-precision ops below intentionally use sz/2-wide operands
+	// producing an sz-wide result, which is why they mask differently.)
 	case LLIL_ADD:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
-		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
+		intx::uint512 right = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(1)), sz);
 		intx::uint512 result = MaskToSize(left + right, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), MaskToSize(right, sz), result, sz, LLIL_ADD, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_ADD, true};
 		return result;
 	}
 
 	case LLIL_SUB:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
-		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
+		intx::uint512 right = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(1)), sz);
 		intx::uint512 result = MaskToSize(left - right, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), MaskToSize(right, sz), result, sz, LLIL_SUB, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_SUB, true};
 		return result;
 	}
 
 	case LLIL_AND:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
-		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
+		intx::uint512 right = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(1)), sz);
 		intx::uint512 result = MaskToSize(left & right, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), MaskToSize(right, sz), result, sz, LLIL_AND, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_AND, true};
 		return result;
 	}
 
 	case LLIL_OR:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
-		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
+		intx::uint512 right = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(1)), sz);
 		intx::uint512 result = MaskToSize(left | right, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), MaskToSize(right, sz), result, sz, LLIL_OR, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_OR, true};
 		return result;
 	}
 
 	case LLIL_XOR:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
-		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
+		intx::uint512 right = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(1)), sz);
 		intx::uint512 result = MaskToSize(left ^ right, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), MaskToSize(right, sz), result, sz, LLIL_XOR, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_XOR, true};
 		return result;
 	}
 
 	case LLIL_LSL:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
 		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
 		size_t shiftAmt = static_cast<uint64_t>(right) & (sz * 8 - 1);
 		intx::uint512 result = MaskToSize(left << shiftAmt, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), right, result, sz, LLIL_LSL, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_LSL, true};
 		return result;
 	}
 
@@ -1080,10 +1084,10 @@ intx::uint512 LLILEmulator::EvalExpr(const LowLevelILInstruction& expr)
 
 	case LLIL_MUL:
 	{
-		intx::uint512 left = EvalExpr(expr.GetRawOperandAsExpr(0));
-		intx::uint512 right = EvalExpr(expr.GetRawOperandAsExpr(1));
+		intx::uint512 left = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(0)), sz);
+		intx::uint512 right = MaskToSize(EvalExpr(expr.GetRawOperandAsExpr(1)), sz);
 		intx::uint512 result = MaskToSize(left * right, sz);
-		m_lastArithmetic = {MaskToSize(left, sz), MaskToSize(right, sz), result, sz, LLIL_MUL, true};
+		m_lastArithmetic = {left, right, result, sz, LLIL_MUL, true};
 		return result;
 	}