evmasm: Don't update free memory pointer for value type returns

Author: r0qs

libsolidity/codegen/ExpressionCompiler.cpp

@@ -2942,11 +2942,10 @@ void ExpressionCompiler::appendExternalFunctionCall(
 		utils().fetchFreeMemoryPointer();
 		// Stack: return_data_start
 
-		// The old decoder did not allocate any memory (i.e. did not touch the free
-		// memory pointer), but kept references to the return data for
-		// (statically-sized) arrays
+		// Only update free memory pointer if any return type needs memory (reference types).
+		// Value types are decoded directly to the stack via mload.
 		bool needToUpdateFreeMemoryPtr = false;
-		if (dynamicReturnSize || m_context.useABICoderV2())
+		if (dynamicReturnSize)
 			needToUpdateFreeMemoryPtr = true;
 		else
 			for (auto const& retType: returnTypes)

test/libsolidity/semanticTests/abiEncoderV1/external_call_static_array_allocates_memory.sol

@@ -0,0 +1,44 @@
+pragma abicoder v1;
+
+interface I {
+    function getStaticArray() external returns (uint[2] memory);
+}
+
+contract Impl is I {
+    function getStaticArray() external pure returns (uint[2] memory) {
+        uint[2] memory arr;
+        arr[0] = 1;
+        arr[1] = 2;
+        return arr;
+    }
+}
+
+// With ABIEncoderV1, static arrays allocate memory for returndata buffer.
+// The decoded array is in place, so only returndata buffer is allocated.
+contract C {
+    I immutable impl = I(address(new Impl()));
+
+    function freeMemory() internal pure returns (uint m) { assembly { m := mload(0x40) } }
+
+    // 64 = returndata buffer only (decoded in place)
+    function testStaticArray() public returns (uint memDiff) {
+        uint memBefore = freeMemory();
+        impl.getStaticArray();
+        memDiff = freeMemory() - memBefore;
+    }
+
+    // 640 = 10 calls * 64 bytes per call
+    function testMemoryGrowsInLoop() public returns (uint memDiff) {
+        uint memBefore = freeMemory();
+        for (uint i = 0; i < 10; i++) {
+            impl.getStaticArray();
+        }
+        memDiff = freeMemory() - memBefore;
+    }
+}
+// ====
+// EVMVersion: >=byzantium
+// compileViaYul: false
+// ----
+// testStaticArray() -> 64
+// testMemoryGrowsInLoop() -> 640

test/libsolidity/semanticTests/abiEncoderV1/external_call_value_type_no_memory_allocation.sol

@@ -0,0 +1,34 @@
+pragma abicoder v1;
+
+interface I {
+    function getUint() external returns (uint256);
+}
+
+contract Impl is I {
+    function getUint() external pure returns (uint256) { return 42; }
+}
+
+contract C {
+    I immutable impl = I(address(new Impl()));
+
+    function freeMemory() internal pure returns (uint m) { assembly { m := mload(0x40) } }
+
+    function testValueType() public returns (uint memDiff) {
+        uint memBefore = freeMemory();
+        impl.getUint();
+        memDiff = freeMemory() - memBefore;
+    }
+
+    function testNoMemoryGrowthInLoop() public returns (uint memDiff) {
+        uint memBefore = freeMemory();
+        for (uint i = 0; i < 10; i++) {
+            impl.getUint();
+        }
+        memDiff = freeMemory() - memBefore;
+    }
+}
+// ====
+// compileViaYul: false
+// ----
+// testValueType() -> 0
+// testNoMemoryGrowthInLoop() -> 0

test/libsolidity/semanticTests/abiEncoderV1/struct/struct_storage_ptr.sol

@@ -25,5 +25,5 @@ contract C {
 // library: L
 // f() -> 8, 7, 1, 2, 7, 12
 // gas irOptimized: 166609
-// gas legacy: 170486
-// gas legacyOptimized: 167252
+// gas legacy: 170439
+// gas legacyOptimized: 167202

test/libsolidity/semanticTests/abiEncoderV2/external_call_value_type_no_memory_allocation.sol

@@ -0,0 +1,32 @@
+pragma abicoder v2;
+
+interface I {
+    function getUint() external returns (uint256);
+}
+
+contract Impl is I {
+    function getUint() external pure returns (uint256) { return 42; }
+}
+
+contract C {
+    I immutable impl = I(address(new Impl()));
+
+    function freeMemory() internal pure returns (uint m) { assembly { m := mload(0x40) } }
+
+    function testValueType() public returns (uint memDiff) {
+        uint memBefore = freeMemory();
+        impl.getUint();
+        memDiff = freeMemory() - memBefore;
+    }
+
+    function testNoMemoryGrowthInLoop() public returns (uint memDiff) {
+        uint memBefore = freeMemory();
+        for (uint i = 0; i < 10; i++) {
+            impl.getUint();
+        }
+        memDiff = freeMemory() - memBefore;
+    }
+}
+// ----
+// testValueType() -> 0
+// testNoMemoryGrowthInLoop() -> 0

test/libsolidity/semanticTests/arithmetics/check_var_init.sol

@@ -16,5 +16,5 @@ contract D {
 // ----
 // f() -> FAILURE, hex"4e487b71", 0x11
 // g(), 100 wei -> 1
-// gas legacy: 76780
+// gas legacy: 76745
 // gas legacy code: 23600

test/libsolidity/semanticTests/array/function_array_cross_calls.sol

@@ -44,7 +44,7 @@ contract C {
 // test() -> 5, 6, 7
 // gas irOptimized: 85886
 // gas irOptimized code: 158000
-// gas legacy: 97551
-// gas legacy code: 342800
-// gas legacyOptimized: 87808
-// gas legacyOptimized code: 193000
+// gas legacy: 97317
+// gas legacy code: 333800
+// gas legacyOptimized: 87541
+// gas legacyOptimized code: 183400

test/libsolidity/semanticTests/array/reusing_memory.sol

@@ -26,7 +26,7 @@ contract Main {
 // f(uint256): 0x34 -> 0x46bddb1178e94d7f2892ff5f366840eb658911794f2c3a44c450aa2c505186c1
 // gas irOptimized: 99328
 // gas irOptimized code: 12400
-// gas legacy: 101551
+// gas legacy: 101478
 // gas legacy code: 23600
-// gas legacyOptimized: 99612
+// gas legacyOptimized: 99533
 // gas legacyOptimized code: 13400

test/libsolidity/semanticTests/constructor/arrays_in_constructors.sol

@@ -28,7 +28,7 @@ contract Creator {
 // f(uint256,address[]): 7, 0x40, 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 -> 7, 8
 // gas irOptimized: 327542
 // gas irOptimized code: 94000
-// gas legacy: 338477
+// gas legacy: 338407
 // gas legacy code: 244800
-// gas legacyOptimized: 329166
+// gas legacyOptimized: 329090
 // gas legacyOptimized code: 117000

test/libsolidity/semanticTests/constructor/bytes_in_constructors_packer.sol

@@ -28,7 +28,7 @@ contract Creator {
 // f(uint256,bytes): 7, 0x40, 78, "abcdefghijklmnopqrstuvwxyzabcdef", "ghijklmnopqrstuvwxyzabcdefghijkl", "mnopqrstuvwxyz" -> 7, "h"
 // gas irOptimized: 169055
 // gas irOptimized code: 99600
-// gas legacy: 172946
+// gas legacy: 172876
 // gas legacy code: 239800
-// gas legacyOptimized: 169823
+// gas legacyOptimized: 169747
 // gas legacyOptimized code: 118600