SSA-CFG: Add pass to simplify negated condtions

When a jumo condition is a boolean negation (`iszero`), we can
remove the negation and swap the zero and non-zero successors.

This commit just adds the pass, but does not run it yet.

Author: blishko

libyul/CMakeLists.txt

@@ -110,6 +110,8 @@ add_library(yul
 	backends/evm/ssa/io/DotExporterBase.h
 	backends/evm/ssa/io/JSONExporter.cpp
 	backends/evm/ssa/io/JSONExporter.h
+	backends/evm/ssa/transform/JumpConditionSimplifier.cpp
+	backends/evm/ssa/transform/JumpConditionSimplifier.h
 	backends/evm/ssa/transform/TrivialPhiEliminator.cpp
 	backends/evm/ssa/transform/TrivialPhiEliminator.h
 	backends/evm/ssa/transform/UnreachableBlockCleaner.cpp

libyul/backends/evm/ssa/transform/JumpConditionSimplifier.cpp

@@ -0,0 +1,51 @@
+/*
+	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/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+
+#include <libyul/backends/evm/ssa/transform/JumpConditionSimplifier.h>
+
+#include <libyul/backends/evm/ssa/SSACFG.h>
+
+namespace solidity::yul::ssa::transform
+{
+void simplifyNegatedJumpConditions(SSACFG& _cfg)
+{
+	auto const maybeIsZero = _cfg.evmDialect.booleanNegationFunctionHandle();
+	if (!maybeIsZero)
+		return;
+	auto const booleanNegationHandle = *maybeIsZero;
+	for (SSACFG::BlockId blockId{0}; blockId.value < _cfg.numBlocks(); ++blockId.value)
+	{
+		auto & block = _cfg.block(blockId);
+		if (!std::holds_alternative<SSACFG::BasicBlock::ConditionalJump>(block.exit))
+			continue;
+		auto & conditionalJump = std::get<SSACFG::BasicBlock::ConditionalJump>(block.exit);
+		auto const condition = conditionalJump.condition;
+		auto const & instruction = _cfg.inst(condition);
+		if (instruction.opcode != InstOpcode::BuiltinCall)
+			continue;
+
+		if (_cfg.builtinPayload(condition).builtin != booleanNegationHandle)
+			continue;
+		yulAssert(instruction.inputs.size() == 1);
+		auto const arg = instruction.inputs.at(0);
+		conditionalJump.condition = arg;
+		std::swap(conditionalJump.zero, conditionalJump.nonZero);
+	}
+}
+}
+

libyul/backends/evm/ssa/transform/JumpConditionSimplifier.h

@@ -0,0 +1,37 @@
+/*
+	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/>.
+*/
+// SPDX-License-Identifier: GPL-3.0
+/**
+ * Removes trivial phis from an SSA CFG.
+ *
+ * A phi is trivial if all its upsilon operands provide the same value (modulo self-references).
+ * Removal may cascade: eliminating one trivial phi can make others trivial.
+ */
+#pragma once
+
+namespace solidity::yul::ssa
+{
+class SSACFG;
+namespace transform
+{
+
+/// Removes unreachable blocks and cleans up references to them.
+void simplifyNegatedJumpConditions(SSACFG & _cfg);
+}
+}
+
+