Implement signed subtraction for sol->yul code generation.

libsolidity/codegen/YulUtilFunctions.cpp

@@ -464,18 +464,28 @@ string YulUtilFunctions::overflowCheckedIntDivFunction(IntegerType const& _type)
 	});
 }
 
-string YulUtilFunctions::overflowCheckedUIntSubFunction()
+string YulUtilFunctions::overflowCheckedIntSubFunction(IntegerType const& _type)
 {
-	string functionName = "checked_sub_uint";
+	string functionName = "checked_sub_" + _type.identifier();
 	return m_functionCollector->createFunction(functionName, [&] {
 		return
 			Whiskers(R"(
 			function <functionName>(x, y) -> diff {
+				<?signed>
+					// underflow, if y >= 0 and x < (minValue + y)
+					if and(iszero(slt(y, 0)), slt(x, add(<minValue>, y))) { revert(0, 0) }
+					// overflow, if y < 0 and x > (maxValue + y)
+					if and(slt(y, 0), sgt(x, add(<maxValue>, y))) { revert(0, 0) }
+				<!signed>
 					if lt(x, y) { revert(0, 0) }
+				</signed>
 				diff := sub(x, y)
 			}
 			)")
 			("functionName", functionName)
+			("signed", _type.isSigned())
+			("maxValue", toCompactHexWithPrefix(u256(_type.maxValue())))
+			("minValue", toCompactHexWithPrefix(u256(_type.minValue())))
 			.render();
 	});
 }

libsolidity/codegen/YulUtilFunctions.h

@@ -106,7 +106,7 @@ public:
 	/// @returns computes the difference between two values.
 	/// Assumes the input to be in range for the type.
 	/// signature: (x, y) -> diff
-	std::string overflowCheckedUIntSubFunction();
+	std::string overflowCheckedIntSubFunction(IntegerType const& _type);
 
 	/// @returns the name of a function that fetches the length of the given
 	/// array

libsolidity/codegen/ir/IRGeneratorForStatements.cpp

@@ -1133,8 +1133,7 @@ string IRGeneratorForStatements::binaryOperation(
 				fun = m_utils.overflowCheckedIntAddFunction(*type);
 				break;
 			case Token::Sub:
-				if (!type->isSigned())
+				fun = m_utils.overflowCheckedIntSubFunction(*type);
-					fun = m_utils.overflowCheckedUIntSubFunction();
 				break;
 			case Token::Mul:
 				if (!type->isSigned())

test/libsolidity/semanticTests/viaYul/detect_sub_overflow.sol

@@ -0,0 +1,17 @@
+contract C {
+    function f(uint a, uint b) public pure returns (uint x) {
+        x = a - b;
+    }
+    function g(uint8 a, uint8 b) public pure returns (uint8 x) {
+        x = a - b;
+    }
+}
+// ====
+// compileViaYul: true
+// ----
+// f(uint256,uint256): 6, 5 -> 1
+// f(uint256,uint256): 6, 6 -> 0
+// f(uint256,uint256): 5, 6 -> FAILURE
+// g(uint8,uint8): 6, 5 -> 1
+// g(uint8,uint8): 6, 6 -> 0
+// g(uint8,uint8): 5, 6 -> FAILURE

test/libsolidity/semanticTests/viaYul/detect_sub_overflow_signed.sol

@@ -0,0 +1,42 @@
+contract C {
+    function f(int a, int b) public pure returns (int x) {
+        x = a - b;
+    }
+    function g(int8 a, int8 b) public pure returns (int8 x) {
+        x = a - b;
+    }
+}
+// ====
+// compileViaYul: true
+// ----
+// f(int256,int256): 5, 6 -> -1
+// f(int256,int256): -2, 1 -> -3
+// f(int256,int256): -2, 2 -> -4
+// f(int256,int256): 2, -2 -> 4
+// f(int256,int256): 2, 2 -> 0
+// f(int256,int256): -5, -6 -> 1
+// f(int256,int256): 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF0, -15 -> 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+// f(int256,int256): 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF0, -16 -> FAILURE
+// f(int256,int256): 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF, -1 -> FAILURE
+// f(int256,int256): 15, 0x8000000000000000000000000000000000000000000000000000000000000010 -> 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
+// f(int256,int256): 16, 0x8000000000000000000000000000000000000000000000000000000000000010 -> FAILURE
+// f(int256,int256): 1, 0x8000000000000000000000000000000000000000000000000000000000000000 -> FAILURE
+// f(int256,int256): -1, 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF -> 0x8000000000000000000000000000000000000000000000000000000000000000
+// f(int256,int256): -2, 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF -> FAILURE
+// f(int256,int256): 0x8000000000000000000000000000000000000000000000000000000000000001, 1 -> 0x8000000000000000000000000000000000000000000000000000000000000000
+// f(int256,int256): 0x8000000000000000000000000000000000000000000000000000000000000001, 2 -> FAILURE
+// f(int256,int256): 0x8000000000000000000000000000000000000000000000000000000000000000, 1 -> FAILURE
+// g(int8,int8): 5, 6 -> -1
+// g(int8,int8): -2, 1 -> -3
+// g(int8,int8): -2, 2 -> -4
+// g(int8,int8): 2, -2 -> 4
+// g(int8,int8): 2, 2 -> 0
+// g(int8,int8): -5, -6 -> 1
+// g(int8,int8): 126, -1 -> 127
+// g(int8,int8): 1, -126 -> 127
+// g(int8,int8): 127, -1 -> FAILURE
+// g(int8,int8): 1, -127 -> FAILURE
+// g(int8,int8): -127, 1 -> -128
+// g(int8,int8): -1, 127 -> -128
+// g(int8,int8): -127, 2 -> FAILURE
+// g(int8,int8): -2, 127 -> FAILURE