8 files changed, 171 insertions, 2 deletions
diff --git a/libdevcore/CommonData.h b/libdevcore/CommonData.h
index 98136b44..f208c425 100644
--- a/libdevcore/CommonData.h
+++ b/libdevcore/CommonData.h
@@ -239,9 +239,10 @@ bool contains(T const& _t, V const& _v)
 /// on the current element and after that. The actual replacement takes
 /// place at the end, but already visited elements might be invalidated.
 /// If nothing is replaced, no copy is performed.
-template <class T>
-void iterateReplacing(std::vector<T>& _vector, std::function<boost::optional<std::vector<T>>(T&)> _f)
+template <typename T, typename F>
+void iterateReplacing(std::vector<T>& _vector, const F& _f)
 {
+	// Concept: _f must be Callable, must accept param T&, must return optional<vector<T>>
 	bool useModified = false;
 	std::vector<T> modifiedVector;
 	for (size_t i = 0; i < _vector.size(); ++i)
diff --git a/libyul/optimiser/BlockFlattener.cpp b/libyul/optimiser/BlockFlattener.cpp
new file mode 100644
index 00000000..04f3ad7f
--- /dev/null
+++ b/libyul/optimiser/BlockFlattener.cpp
@@ -0,0 +1,41 @@
+/*
+	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/BlockFlattener.h>
+#include <libsolidity/inlineasm/AsmData.h>
+#include <libdevcore/Visitor.h>
+#include <libdevcore/CommonData.h>
+#include <functional>
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+
+void BlockFlattener::operator()(Block& _block)
+{
+	ASTModifier::operator()(_block);
+
+	iterateReplacing(
+		_block.statements,
+		[](Statement& _s) -> boost::optional<vector<Statement>>
+		{
+			if (_s.type() == typeid(Block))
+				return std::move(boost::get<Block>(_s).statements);
+			else
+				return {};
+		}
+	);
+}
diff --git a/libyul/optimiser/BlockFlattener.h b/libyul/optimiser/BlockFlattener.h
new file mode 100644
index 00000000..88c49dda
--- /dev/null
+++ b/libyul/optimiser/BlockFlattener.h
@@ -0,0 +1,34 @@
+/*
+	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
+{
+
+class BlockFlattener: public ASTModifier
+{
+public:
+	using ASTModifier::operator();
+	void operator()(Block& _block) override;
+};
+
+}
+}
diff --git a/test/libyul/YulOptimizerTest.cpp b/test/libyul/YulOptimizerTest.cpp
index 8b37830f..ea8e4b5e 100644
--- a/test/libyul/YulOptimizerTest.cpp
+++ b/test/libyul/YulOptimizerTest.cpp
@@ -21,6 +21,7 @@
 
 #include <test/Options.h>
 
+#include <libyul/optimiser/BlockFlattener.h>
 #include <libyul/optimiser/Disambiguator.h>
 #include <libyul/optimiser/CommonSubexpressionEliminator.h>
 #include <libyul/optimiser/NameCollector.h>
@@ -93,6 +94,11 @@ bool YulOptimizerTest::run(ostream& _stream, string const& _linePrefix, bool con
 
 	if (m_optimizerStep == "disambiguator")
 		disambiguate();
+	else if (m_optimizerStep == "blockFlattener")
+	{
+		disambiguate();
+		BlockFlattener{}(*m_ast);
+	}
 	else if (m_optimizerStep == "commonSubexpressionEliminator")
 	{
 		disambiguate();
diff --git a/test/libyul/yulOptimizerTests/blockFlattener/basic.yul b/test/libyul/yulOptimizerTests/blockFlattener/basic.yul
new file mode 100644
index 00000000..adcaedd0
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/blockFlattener/basic.yul
@@ -0,0 +1,20 @@
+{
+  let _1 := mload(0)
+  let f_a := mload(1)
+  let f_r
+  {
+    f_a := mload(f_a)
+    f_r := add(f_a, calldatasize())
+  }
+  let z := mload(2)
+}
+// ----
+// blockFlattener
+// {
+//     let _1 := mload(0)
+//     let f_a := mload(1)
+//     let f_r
+//     f_a := mload(f_a)
+//     f_r := add(f_a, calldatasize())
+//     let z := mload(2)
+// }
diff --git a/test/libyul/yulOptimizerTests/blockFlattener/for_stmt.yul b/test/libyul/yulOptimizerTests/blockFlattener/for_stmt.yul
new file mode 100644
index 00000000..07bd5c18
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/blockFlattener/for_stmt.yul
@@ -0,0 +1,19 @@
+{
+    for { let a := 1 } iszero(eq(a, 10)) { a := add(a, 1) } {
+        a := add(a, 1)
+    }
+}
+// ----
+// blockFlattener
+// {
+//     for {
+//         let a := 1
+//     }
+//     iszero(eq(a, 10))
+//     {
+//         a := add(a, 1)
+//     }
+//     {
+//         a := add(a, 1)
+//     }
+// }
diff --git a/test/libyul/yulOptimizerTests/blockFlattener/if_stmt.yul b/test/libyul/yulOptimizerTests/blockFlattener/if_stmt.yul
new file mode 100644
index 00000000..4d6ccf0e
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/blockFlattener/if_stmt.yul
@@ -0,0 +1,20 @@
+{
+  if add(mload(7), sload(mload(3)))
+  {
+    let y := add(mload(3), 3)
+	{
+      y := add(y, 7)
+	}
+  }
+  let t := add(3, 9)
+}
+// ----
+// blockFlattener
+// {
+//     if add(mload(7), sload(mload(3)))
+//     {
+//         let y := add(mload(3), 3)
+//         y := add(y, 7)
+//     }
+//     let t := add(3, 9)
+// }
diff --git a/test/libyul/yulOptimizerTests/blockFlattener/many_nested_blocks.yul b/test/libyul/yulOptimizerTests/blockFlattener/many_nested_blocks.yul
new file mode 100644
index 00000000..ae2a066b
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/blockFlattener/many_nested_blocks.yul
@@ -0,0 +1,28 @@
+{
+  let a := 3
+  let b := 4
+  {
+    a := add(b, 3)
+    let c := 5
+    {
+      b := add(b, 4)
+      {
+        c := add(a, 5)
+	  }
+      b := add(a, b)
+    }
+    a := add(a, c)
+  }
+}
+// ----
+// blockFlattener
+// {
+//     let a := 3
+//     let b := 4
+//     a := add(b, 3)
+//     let c := 5
+//     b := add(b, 4)
+//     c := add(a, 5)
+//     b := add(a, b)
+//     a := add(a, c)
+// }