Merge pull request #10341 from ethereum/optimizeAllocation

Do not allocate memory objects if they will be assigned directly.

test/libsolidity/semanticTests/memoryManagement/assembly_access.sol

@@ -0,0 +1,16 @@
+contract C {
+    function f() public pure {
+        uint[] memory x;
+        uint y;
+        assembly {
+            y := x
+        }
+        // The value of an uninitialized dynamic array is not zero but rather
+        // an address of a location in memory that has the value of zero.
+        assert(y != 0);
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f() ->

test/libsolidity/semanticTests/memoryManagement/return_variable.sol

@@ -0,0 +1,30 @@
+contract C {
+    function memorySize() internal pure returns (uint s) {
+        assembly { s := mload(0x40) }
+    }
+    function f() public returns (uint, uint, uint) {
+        uint a = memorySize();
+        g();
+        uint b = memorySize();
+        h();
+        uint c = memorySize();
+        i();
+        uint d = memorySize();
+        return (b - a, c - b, d - c);
+    }
+    // In these functions, we do allocate memory in both cases.
+    // In `i()`, this could be avoided but we would have to check
+    // that all code paths return explicitly and provide a value.
+    function g() internal returns (uint[40] memory) {
+    }
+    function h() internal returns (uint[40] memory t) {
+    }
+    function i() internal returns (uint[40] memory) {
+        uint[40] memory x;
+        return x;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 0x0500, 0x0500, 0x0a00

test/libsolidity/semanticTests/memoryManagement/static_memory_array_allocation.sol

@@ -0,0 +1,24 @@
+contract C {
+    function memorySize() internal pure returns (uint s) {
+        assembly { s := mload(0x40) }
+    }
+    function withValue() public pure returns (uint) {
+        uint[20] memory x;
+        uint memorySizeBefore = memorySize();
+        uint[20] memory t = x;
+        uint memorySizeAfter = memorySize();
+        return memorySizeAfter - memorySizeBefore;
+    }
+    function withoutValue() public pure returns (uint) {
+        uint[20] memory x;
+        uint memorySizeBefore = memorySize();
+        uint[20] memory t;
+        uint memorySizeAfter = memorySize();
+        return memorySizeAfter - memorySizeBefore;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// withValue() -> 0x00
+// withoutValue() -> 0x0280

test/libsolidity/semanticTests/memoryManagement/struct_allocation.sol

@@ -0,0 +1,24 @@
+contract C {
+    struct S { uint x; uint y; uint z; }
+    function memorySize() internal pure returns (uint s) {
+        assembly { s := mload(0x40) }
+    }
+    function withValue() public pure returns (uint) {
+        S memory x = S(1, 2, 3);
+        uint memorySizeBefore = memorySize();
+        S memory t = x;
+        uint memorySizeAfter = memorySize();
+        return memorySizeAfter - memorySizeBefore;
+    }
+    function withoutValue() public pure returns (uint) {
+        uint memorySizeBefore = memorySize();
+        S memory t;
+        uint memorySizeAfter = memorySize();
+        return memorySizeAfter - memorySizeBefore;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// withValue() -> 0x00
+// withoutValue() -> 0x60

test/libsolidity/syntaxTests/scoping/access_in_assignment_dynamic_array.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public pure {
+        uint[] memory x = x[0];
+    }
+}
+// ----
+// DeclarationError 7576: (70-71): Undeclared identifier. "x" is not (or not yet) visible at this point.

test/libsolidity/syntaxTests/scoping/access_in_assignment_struct.sol

@@ -0,0 +1,8 @@
+contract C {
+    struct S { uint y; }
+    function f() public pure {
+        S memory x = x.y;
+    }
+}
+// ----
+// DeclarationError 7576: (90-91): Undeclared identifier. "x" is not (or not yet) visible at this point.