[Yul] Implements a pass to rewrite for-loop's pre block into the parent's Block.

libyul/optimiser/ForLoopInitRewriter.cpp

@@ -0,0 +1,43 @@
+/*
+	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 <http://www.gnu.org/licenses/>.
+*/
+#include <libyul/optimiser/ForLoopInitRewriter.h>
+#include <libsolidity/inlineasm/AsmData.h>
+#include <libdevcore/CommonData.h>
+#include <functional>
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+
+void ForLoopInitRewriter::operator()(Block& _block)
+{
+	iterateReplacing(
+		_block.statements,
+		[](Statement& _stmt) -> boost::optional<vector<Statement>>
+		{
+			if (_stmt.type() == typeid(ForLoop))
+			{
+				auto& forLoop = boost::get<ForLoop>(_stmt);
+				vector<Statement> rewrite;
+				swap(rewrite, forLoop.pre.statements);
+				rewrite.emplace_back(move(forLoop));
+				return rewrite;
+			}
+			return {};
+		}
+	);
+}

libyul/optimiser/ForLoopInitRewriter.h

@@ -0,0 +1,39 @@
+/*
+	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 <http://www.gnu.org/licenses/>.
+*/
+#pragma once
+
+#include <libyul/optimiser/ASTWalker.h>
+
+namespace dev
+{
+namespace yul
+{
+
+/**
+ * Rewrites ForLoop by moving the pre statement block in front of the ForLoop.
+ * Requirements:
+ * - The Disambiguator must be run upfront.
+ */
+class ForLoopInitRewriter: public ASTModifier
+{
+public:
+	using ASTModifier::operator();
+	void operator()(Block& _block) override;
+};
+
+}
+}

libyul/optimiser/Suite.cpp

@@ -27,6 +27,7 @@
 #include <libyul/optimiser/ExpressionJoiner.h>
 #include <libyul/optimiser/ExpressionInliner.h>
 #include <libyul/optimiser/FullInliner.h>
+#include <libyul/optimiser/ForLoopInitRewriter.h>
 #include <libyul/optimiser/Rematerialiser.h>
 #include <libyul/optimiser/UnusedPruner.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
@@ -58,6 +59,7 @@ void OptimiserSuite::run(
 
 	(FunctionHoister{})(ast);
 	(FunctionGrouper{})(ast);
+	(ForLoopInitRewriter{})(ast);
 
 	NameDispenser dispenser{ast};
 

test/libyul/YulOptimizerTest.cpp

@@ -31,6 +31,7 @@
 #include <libyul/optimiser/FunctionHoister.h>
 #include <libyul/optimiser/ExpressionInliner.h>
 #include <libyul/optimiser/FullInliner.h>
+#include <libyul/optimiser/ForLoopInitRewriter.h>
 #include <libyul/optimiser/MainFunction.h>
 #include <libyul/optimiser/Rematerialiser.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
@@ -108,6 +109,11 @@ bool YulOptimizerTest::run(ostream& _stream, string const& _linePrefix, bool con
 		disambiguate();
 		VarDeclPropagator{}(*m_ast);
 	}
+	else if (m_optimizerStep == "forLoopInitRewriter")
+	{
+		disambiguate();
+		ForLoopInitRewriter{}(*m_ast);
+	}
 	else if (m_optimizerStep == "commonSubexpressionEliminator")
 	{
 		disambiguate();

test/libyul/yulOptimizerTests/forLoopInitRewriter/complex_pre.yul

@@ -0,0 +1,23 @@
+{
+  let random := 42
+  for { let a := 1
+	    let b := 1 } iszero(eq(a, 10)) { a := add(a, b) } {
+    a := add(a, 1)
+  }
+}
+// ----
+// forLoopInitRewriter
+// {
+//     let random := 42
+//     let a := 1
+//     let b := 1
+//     for {
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, b)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }

test/libyul/yulOptimizerTests/forLoopInitRewriter/empty_pre.yul

@@ -0,0 +1,20 @@
+{
+  let a := 1
+  for {} iszero(eq(a, 10)) { a := add(a, 1) } {
+    a := add(a, 1)
+  }
+}
+// ----
+// forLoopInitRewriter
+// {
+//     let a := 1
+//     for {
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, 1)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }

test/libyul/yulOptimizerTests/forLoopInitRewriter/simple.yul

@@ -0,0 +1,21 @@
+{
+  let random := 42
+  for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+    a := add(a, 1)
+  }
+}
+// ----
+// forLoopInitRewriter
+// {
+//     let random := 42
+//     let a := 1
+//     for {
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, 1)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }

test/tools/yulopti.cpp

@@ -38,6 +38,7 @@
 #include <libyul/optimiser/FunctionHoister.h>
 #include <libyul/optimiser/ExpressionInliner.h>
 #include <libyul/optimiser/FullInliner.h>
+#include <libyul/optimiser/ForLoopInitRewriter.h>
 #include <libyul/optimiser/MainFunction.h>
 #include <libyul/optimiser/Rematerialiser.h>
 #include <libyul/optimiser/ExpressionSimplifier.h>
@@ -123,7 +124,7 @@ public:
 			}
 			cout << "(q)quit/(f)flatten/(c)se/propagate var(d)ecls/(x)plit/(j)oin/(g)rouper/(h)oister/" << endl;
 			cout << "  (e)xpr inline/(i)nline/(s)implify/(u)nusedprune/ss(a) transform/" << endl;
-			cout << "  (r)edundant assign elim./re(m)aterializer? ";
+			cout << "  (r)edundant assign elim./re(m)aterializer/f(o)r-loop-pre-rewriter? ";
 			cout.flush();
 			int option = readStandardInputChar();
 			cout << ' ' << char(option) << endl;
@@ -134,6 +135,9 @@ public:
 			case 'f':
 				BlockFlattener{}(*m_ast);
 				break;
+			case 'o':
+				ForLoopInitRewriter{}(*m_ast);
+				break;
 			case 'c':
 				(CommonSubexpressionEliminator{})(*m_ast);
 				break;