diff --git a/test/libyul/StackReuseCodegen.cpp b/test/libyul/StackReuseCodegen.cpp
new file mode 100644
index 000000000..97be11d35
--- /dev/null
+++ b/test/libyul/StackReuseCodegen.cpp
@@ -0,0 +1,353 @@
+/*
+ This file is part of solidity.
+
+ solidity is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ solidity is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with solidity. If not, see .
+*/
+/**
+ * Unit tests for stack-reusing code generator.
+ */
+
+#include
+
+#include
+#include
+
+using namespace std;
+
+namespace dev
+{
+namespace yul
+{
+namespace test
+{
+
+namespace
+{
+string assemble(string const& _input)
+{
+ solidity::AssemblyStack asmStack;
+ BOOST_REQUIRE_MESSAGE(asmStack.parseAndAnalyze("", _input), "Source did not parse: " + _input);
+ return solidity::disassemble(asmStack.assemble(solidity::AssemblyStack::Machine::EVM, true).bytecode->bytecode);
+}
+}
+
+BOOST_AUTO_TEST_SUITE(StackReuseCodegen)
+
+BOOST_AUTO_TEST_CASE(smoke_test)
+{
+ string out = assemble("{}");
+ BOOST_CHECK_EQUAL(out, "");
+}
+
+BOOST_AUTO_TEST_CASE(single_var)
+{
+ string out = assemble("{ let x }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x0 POP ");
+}
+
+BOOST_AUTO_TEST_CASE(single_var_assigned)
+{
+ string out = assemble("{ let x := 1 }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x1 POP ");
+}
+
+BOOST_AUTO_TEST_CASE(single_var_assigned_plus_code)
+{
+ string out = assemble("{ let x := 1 mstore(3, 4) }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x1 POP PUSH1 0x4 PUSH1 0x3 MSTORE ");
+}
+
+BOOST_AUTO_TEST_CASE(single_var_assigned_plus_code_and_reused)
+{
+ string out = assemble("{ let x := 1 mstore(3, 4) pop(mload(x)) }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x1 PUSH1 0x4 PUSH1 0x3 MSTORE DUP1 MLOAD POP POP ");
+}
+
+BOOST_AUTO_TEST_CASE(multi_reuse_single_slot)
+{
+ string out = assemble("{ let x := 1 x := 6 let y := 2 y := 4 }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x1 PUSH1 0x6 SWAP1 POP POP PUSH1 0x2 PUSH1 0x4 SWAP1 POP POP ");
+}
+
+BOOST_AUTO_TEST_CASE(multi_reuse_single_slot_nested)
+{
+ string out = assemble("{ let x := 1 x := 6 { let y := 2 y := 4 } }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x1 PUSH1 0x6 SWAP1 POP POP PUSH1 0x2 PUSH1 0x4 SWAP1 POP POP ");
+}
+
+BOOST_AUTO_TEST_CASE(multi_reuse_same_variable_name)
+{
+ string out = assemble("{ let z := mload(0) { let x := 1 x := 6 z := x } { let x := 2 z := x x := 4 } }");
+ BOOST_CHECK_EQUAL(out,
+ "PUSH1 0x0 MLOAD "
+ "PUSH1 0x1 PUSH1 0x6 SWAP1 POP DUP1 SWAP2 POP POP "
+ "PUSH1 0x2 DUP1 SWAP2 POP PUSH1 0x4 SWAP1 POP POP "
+ "POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(last_use_in_nested_block)
+{
+ string out = assemble("{ let z := 0 { pop(z) } let x := 1 }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x0 DUP1 POP POP PUSH1 0x1 POP ");
+}
+
+BOOST_AUTO_TEST_CASE(if_)
+{
+ // z is only removed after the if (after the jumpdest)
+ string out = assemble("{ let z := mload(0) if z { let x := z } let t := 3 }");
+ BOOST_CHECK_EQUAL(out, "PUSH1 0x0 MLOAD DUP1 ISZERO PUSH1 0xA JUMPI DUP1 POP JUMPDEST POP PUSH1 0x3 POP ");
+}
+
+BOOST_AUTO_TEST_CASE(switch_)
+{
+ string out = assemble("{ let z := 0 switch z case 0 { let x := 2 let y := 3 } default { z := 3 } let t := 9 }");
+ BOOST_CHECK_EQUAL(out,
+ "PUSH1 0x0 DUP1 "
+ "PUSH1 0x0 DUP2 EQ PUSH1 0x11 JUMPI "
+ "PUSH1 0x3 SWAP2 POP PUSH1 0x18 JUMP "
+ "JUMPDEST PUSH1 0x2 POP PUSH1 0x3 POP "
+ "JUMPDEST POP POP " // This is where z and its copy (switch condition) can be removed.
+ "PUSH1 0x9 POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(reuse_slots)
+{
+ // x and y should reuse the slots of b and d
+ string out = assemble("{ let a, b, c, d let x := 2 let y := 3 mstore(x, a) mstore(y, c) }");
+ BOOST_CHECK_EQUAL(out,
+ "PUSH1 0x0 PUSH1 0x0 PUSH1 0x0 PUSH1 0x0 "
+ "POP " // d is removed right away
+ "PUSH1 0x2 SWAP2 POP " // x is stored at b's slot
+ "PUSH1 0x3 DUP4 DUP4 MSTORE "
+ "DUP2 DUP2 MSTORE "
+ "POP POP POP POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(for_1)
+{
+ // Special scoping rules, but can remove z early
+ string out = assemble("{ for { let z := 0 } 1 { } { let x := 3 } let t := 2 }");
+ BOOST_CHECK_EQUAL(out,
+ "PUSH1 0x0 POP "
+ "JUMPDEST PUSH1 0x1 ISZERO PUSH1 0x11 JUMPI "
+ "PUSH1 0x3 POP JUMPDEST PUSH1 0x3 JUMP "
+ "JUMPDEST PUSH1 0x2 POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(for_2)
+{
+ // Special scoping rules, cannot remove z until after the loop!
+ string out = assemble("{ for { let z := 0 } 1 { } { z := 8 let x := 3 } let t := 2 }");
+ BOOST_CHECK_EQUAL(out,
+ "PUSH1 0x0 "
+ "JUMPDEST PUSH1 0x1 ISZERO PUSH1 0x14 JUMPI "
+ "PUSH1 0x8 SWAP1 POP "
+ "PUSH1 0x3 POP "
+ "JUMPDEST PUSH1 0x2 JUMP "
+ "JUMPDEST POP " // z is removed
+ "PUSH1 0x2 POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(function_trivial)
+{
+ string in = R"({
+ function f() { }
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x5 JUMP JUMPDEST JUMP JUMPDEST "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(function_retparam)
+{
+ string in = R"({
+ function f() -> x, y { }
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0xB JUMP "
+ "JUMPDEST PUSH1 0x0 PUSH1 0x0 SWAP1 SWAP2 JUMP "
+ "JUMPDEST "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(function_params)
+{
+ string in = R"({
+ function f(a, b) { }
+ })";
+ BOOST_CHECK_EQUAL(assemble(in), "PUSH1 0x7 JUMP JUMPDEST POP POP JUMP JUMPDEST ");
+}
+
+BOOST_AUTO_TEST_CASE(function_params_and_retparams)
+{
+ string in = R"({
+ function f(a, b, c, d) -> x, y { }
+ })";
+ // This does not re-use the parameters for the return parameters
+ // We do not expect parameters to be fully unused, so the stack
+ // layout for a function is still fixed, even though parameters
+ // can be re-used.
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x10 JUMP JUMPDEST PUSH1 0x0 PUSH1 0x0 SWAP5 POP SWAP5 SWAP3 POP POP POP JUMP JUMPDEST "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(function_params_and_retparams_partly_unused)
+{
+ string in = R"({
+ function f(a, b, c, d) -> x, y { b := 3 let s := 9 y := 2 mstore(s, y) }
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x1E JUMP "
+ "JUMPDEST PUSH1 0x0 PUSH1 0x0 "
+ "PUSH1 0x3 SWAP4 POP "
+ "PUSH1 0x9 PUSH1 0x2 SWAP2 POP "
+ "DUP2 DUP2 MSTORE "
+ "POP SWAP5 POP SWAP5 SWAP3 POP POP POP JUMP "
+ "JUMPDEST "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(function_with_body_embedded)
+{
+ string in = R"({
+ let b := 3
+ function f(a, r) -> t {
+ // r could be removed right away, but a cannot - this is not implemented, though
+ let x := a a := 3 t := a
+ }
+ b := 7
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x3 PUSH1 "
+ "0x16 JUMP "
+ "JUMPDEST PUSH1 0x0 " // start of f, initialize t
+ "DUP2 POP " // let x := a
+ "PUSH1 0x3 SWAP2 POP "
+ "DUP2 SWAP1 POP "
+ "SWAP3 SWAP2 POP POP JUMP "
+ "JUMPDEST PUSH1 0x7 SWAP1 "
+ "POP POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(function_call)
+{
+ string in = R"({
+ let b := f(1, 2)
+ function f(a, r) -> t { }
+ b := f(3, 4)
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x9 PUSH1 0x2 PUSH1 0x1 PUSH1 0xD JUMP "
+ "JUMPDEST PUSH1 0x15 JUMP " // jump over f
+ "JUMPDEST PUSH1 0x0 SWAP3 SWAP2 POP POP JUMP " // f
+ "JUMPDEST PUSH1 0x1F PUSH1 0x4 PUSH1 0x3 PUSH1 0xD JUMP "
+ "JUMPDEST SWAP1 POP POP "
+ );
+}
+
+
+BOOST_AUTO_TEST_CASE(functions_multi_return)
+{
+ string in = R"({
+ function f(a, b) -> t { }
+ function g() -> r, s { }
+ let x := f(1, 2)
+ x := f(3, 4)
+ let y, z := g()
+ y, z := g()
+ let unused := 7
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0xB JUMP "
+ "JUMPDEST PUSH1 0x0 SWAP3 SWAP2 POP POP JUMP " // f
+ "JUMPDEST PUSH1 0x17 JUMP "
+ "JUMPDEST PUSH1 0x0 PUSH1 0x0 SWAP1 SWAP2 JUMP " // g
+ "JUMPDEST PUSH1 0x21 PUSH1 0x2 PUSH1 0x1 PUSH1 0x3 JUMP " // f(1, 2)
+ "JUMPDEST PUSH1 0x2B PUSH1 0x4 PUSH1 0x3 PUSH1 0x3 JUMP " // f(3, 4)
+ "JUMPDEST SWAP1 POP " // assignment to x
+ "POP " // remove x
+ "PUSH1 0x34 PUSH1 0xF JUMP " // g()
+ "JUMPDEST PUSH1 0x3A PUSH1 0xF JUMP " // g()
+ "JUMPDEST SWAP2 POP SWAP2 POP " // assignments
+ "POP POP " // removal of y and z
+ "PUSH1 0x7 POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(reuse_slots_function)
+{
+ string in = R"({
+ function f() -> x, y, z, t {}
+ let a, b, c, d := f() let x1 := 2 let y1 := 3 mstore(x1, a) mstore(y1, c)
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x11 JUMP "
+ "JUMPDEST PUSH1 0x0 PUSH1 0x0 PUSH1 0x0 PUSH1 0x0 SWAP1 SWAP2 SWAP3 SWAP4 JUMP "
+ "JUMPDEST PUSH1 0x17 PUSH1 0x3 JUMP "
+ // Stack: a b c d
+ "JUMPDEST POP " // d is unused
+ // Stack: a b c
+ "PUSH1 0x2 SWAP2 POP " // x1 reuses b's slot
+ "PUSH1 0x3 "
+ // Stack: a x1 c y1
+ "DUP4 DUP4 MSTORE "
+ "DUP2 DUP2 MSTORE "
+ "POP POP POP POP "
+ );
+}
+
+BOOST_AUTO_TEST_CASE(reuse_slots_function_with_gaps)
+{
+ string in = R"({
+ // Only x3 is actually used, the slots of
+ // x1 and x2 will be reused right away.
+ let x1 := 5 let x2 := 6 let x3 := 7
+ mstore(x1, x2)
+ function f() -> x, y, z, t {}
+ let a, b, c, d := f() mstore(x3, a) mstore(c, d)
+ })";
+ BOOST_CHECK_EQUAL(assemble(in),
+ "PUSH1 0x5 PUSH1 0x6 PUSH1 0x7 "
+ "DUP2 DUP4 MSTORE "
+ "PUSH1 0x1A JUMP " // jump across function
+ "JUMPDEST PUSH1 0x0 PUSH1 0x0 PUSH1 0x0 PUSH1 0x0 SWAP1 SWAP2 SWAP3 SWAP4 JUMP "
+ "JUMPDEST PUSH1 0x20 PUSH1 0xC JUMP "
+ // stack: x1 x2 x3 a b c d
+ "JUMPDEST SWAP6 POP " // move d into x1
+ // stack: d x2 x3 a b c
+ "SWAP4 POP "
+ // stack: d c x3 a b
+ "POP "
+ // stack: d c x3 a
+ "DUP1 DUP3 MSTORE "
+ "POP POP "
+ // stack: d c
+ "DUP2 DUP2 MSTORE "
+ "POP POP "
+ );
+}
+
+
+BOOST_AUTO_TEST_SUITE_END()
+
+}
+}
+}