[YulOpt] Implement loop-invariant code motion

test/libyul/YulOptimizerTest.cpp

@@ -41,6 +41,7 @@
 #include <libyul/optimiser/ForLoopConditionOutOfBody.h>
 #include <libyul/optimiser/ForLoopInitRewriter.h>
 #include <libyul/optimiser/LoadResolver.h>
+#include <libyul/optimiser/LoopInvariantCodeMotion.h>
 #include <libyul/optimiser/MainFunction.h>
 #include <libyul/optimiser/NameDisplacer.h>
 #include <libyul/optimiser/Rematerialiser.h>
@@ -279,6 +280,12 @@ TestCase::TestResult YulOptimizerTest::run(ostream& _stream, string const& _line
 		ExpressionJoiner::run(*m_context, *m_ast);
 		ExpressionJoiner::run(*m_context, *m_ast);
 	}
+	else if (m_optimizerStep == "loopInvariantCodeMotion")
+	{
+		disambiguate();
+		ForLoopInitRewriter::run(*m_context, *m_ast);
+		LoopInvariantCodeMotion::run(*m_context, *m_ast);
+	}
 	else if (m_optimizerStep == "controlFlowSimplifier")
 	{
 		disambiguate();

test/libyul/yulOptimizerTests/fullSuite/abi_example1.yul

@@ -483,7 +483,7 @@
 //         let _5 := 0xffffffffffffffff
 //         if gt(offset, _5) { revert(_1, _1) }
 //         let value2 := abi_decode_t_array$_t_uint256_$dyn_memory_ptr(add(_4, offset), _3)
-//         let offset_1 := calldataload(add(_4, 96))
+//         let offset_1 := calldataload(add(_4, 0x60))
 //         if gt(offset_1, _5) { revert(_1, _1) }
 //         let value3 := abi_decode_t_array$_t_array$_t_uint256_$2_memory_$dyn_memory_ptr(add(_4, offset_1), _3)
 //         sstore(calldataload(_4), calldataload(add(_4, 0x20)))

test/libyul/yulOptimizerTests/fullSuite/aztec.yul

@@ -311,7 +311,7 @@
 //             }
 //             b := add(b, _5)
 //         }
-//         if lt(m, n) { validatePairing(0x64) }
+//         if lt(m, n) { validatePairing(100) }
 //         if iszero(eq(mod(keccak256(0x2a0, add(b, not(671))), _2), challenge))
 //         {
 //             mstore(0, 404)

test/libyul/yulOptimizerTests/fullSuite/clear_after_if_continue.yul

@@ -12,7 +12,7 @@
 // {
 //     {
 //         let y := mload(0x20)
-//         for { } and(y, 8) { if y { revert(0, 0) } }
+//         for { } iszero(iszero(and(y, 8))) { if y { revert(0, 0) } }
 //         {
 //             if y { continue }
 //             sstore(1, 0)

test/libyul/yulOptimizerTests/fullSuite/loopInvariantCodeMotion.yul

@@ -0,0 +1,34 @@
+{
+    sstore(0, array_sum(calldataload(0)))
+
+    function array_sum(x) -> sum {
+        let length := calldataload(x)
+        for { let i := 0 } lt(i, length) { i := add(i, 1) } {
+            sum := add(sum, array_load(x, i))
+        }
+    }
+    function array_load(x, i) -> v {
+        let len := calldataload(x)
+        if iszero(lt(i, len)) { revert(0, 0) }
+        let data := add(x, 0x20)
+        v := calldataload(add(data, mul(i, 0x20)))
+        // this is just to have some additional code that
+        // can be moved out of the loop.
+        v := add(v, calldataload(7))
+    }
+}
+// ====
+// step: fullSuite
+// ----
+// {
+//     {
+//         let _1 := calldataload(0)
+//         let sum := 0
+//         let i := sum
+//         for { } lt(i, calldataload(_1)) { i := add(i, 1) }
+//         {
+//             sum := add(sum, add(calldataload(add(add(_1, mul(i, 0x20)), 0x20)), calldataload(7)))
+//         }
+//         sstore(0, sum)
+//     }
+// }

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/dependOnVarInLoop.yul

@@ -0,0 +1,23 @@
+{
+  let b := 1
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    let c := mload(3)    // c cannot be moved because non-movable
+    let not_inv := add(b, c) // no_inv cannot be moved because its value depends on c
+    a := add(a, 1)
+    mstore(a, not_inv)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 1
+//     let a := 1
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         let c := mload(3)
+//         let not_inv := add(b, c)
+//         a := add(a, 1)
+//         mstore(a, not_inv)
+//     }
+// }

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/multi.yul

@@ -0,0 +1,26 @@
+{
+  let b := 1
+  // tests if c, d, and inv can be moved outside in single pass
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    let c := b
+    let d := mul(c, 2)
+    let inv := add(c, d)
+    a := add(a, 1)
+    mstore(a, inv)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 1
+//     let a := 1
+//     let c := b
+//     let d := mul(c, 2)
+//     let inv := add(c, d)
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         a := add(a, 1)
+//         mstore(a, inv)
+//     }
+// }

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/non-ssavar.yul

@@ -0,0 +1,23 @@
+{
+  let b := 1
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    let not_inv := add(b, 42)
+    not_inv := add(not_inv, 1)
+    a := add(a, 1)
+    mstore(a, not_inv)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 1
+//     let a := 1
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         let not_inv := add(b, 42)
+//         not_inv := add(not_inv, 1)
+//         a := add(a, 1)
+//         mstore(a, not_inv)
+//     }
+// }

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/nonMovable.yul

@@ -0,0 +1,21 @@
+{
+  let b := 0
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    let inv := mload(b)
+    a := add(a, 1)
+    mstore(a, inv)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 0
+//     let a := 1
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         let inv := mload(b)
+//         a := add(a, 1)
+//         mstore(a, inv)
+//     }
+// }

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/recursive.yul

@@ -0,0 +1,25 @@
+{
+  let b := 1
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    for { let a2 := 1 } iszero(eq(a2, 10)) { a2 := add(a2, 1) } {
+      let inv := add(b, 42)
+      mstore(a, inv)
+    }
+    a := add(a, 1)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 1
+//     let a := 1
+//     let inv := add(b, 42)
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         let a2 := 1
+//         for { } iszero(eq(a2, 10)) { a2 := add(a2, 1) }
+//         { mstore(a, inv) }
+//         a := add(a, 1)
+//     }
+// }

test/libyul/yulOptimizerTests/loopInvariantCodeMotion/simple.yul

@@ -0,0 +1,21 @@
+{
+  let b := 1
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    let inv := add(b, 42)
+    a := add(a, 1)
+    mstore(a, inv)
+  }
+}
+// ====
+// step: loopInvariantCodeMotion
+// ----
+// {
+//     let b := 1
+//     let a := 1
+//     let inv := add(b, 42)
+//     for { } iszero(eq(a, 10)) { a := add(a, 1) }
+//     {
+//         a := add(a, 1)
+//         mstore(a, inv)
+//     }
+// }

test/tools/yulopti.cpp

@@ -62,6 +62,7 @@
 #include <libyul/optimiser/VarDeclInitializer.h>
 #include <libyul/optimiser/VarNameCleaner.h>
 #include <libyul/optimiser/LoadResolver.h>
+#include <libyul/optimiser/LoopInvariantCodeMotion.h>
 
 #include <libyul/backends/evm/EVMDialect.h>
 
@@ -142,7 +143,7 @@ public:
 			cout << "  (r)edundant assign elim./re(m)aterializer/f(o)r-loop-init-rewriter/for-loop-condition-(I)nto-body/" << endl;
 			cout << "  for-loop-condition-(O)ut-of-body/s(t)ructural simplifier/equi(v)alent function combiner/ssa re(V)erser/" << endl;
 			cout << "  co(n)trol flow simplifier/stack com(p)ressor/(D)ead code eliminator/(L)oad resolver/" << endl;
-			cout << "  (C)onditional simplifier?" << endl;
+			cout << "  (C)onditional simplifier/loop-invariant code (M)otion?" << endl;
 			cout.flush();
 			int option = readStandardInputChar();
 			cout << ' ' << char(option) << endl;
@@ -237,6 +238,9 @@ public:
 			case 'L':
 				LoadResolver::run(context, *m_ast);
 				break;
+			case 'M':
+				LoopInvariantCodeMotion::run(context, *m_ast);
+				break;
 			default:
 				cout << "Unknown option." << endl;
 			}