[yul] Implements EVM codegen for break/continue plus respective tests & ChangeLog entry.

Author: christianparpart

Changelog.md

@@ -4,6 +4,7 @@ Language Features:
 
 
 Compiler Features:
+ * Yul: Adds break and continue keywords to for-loop syntax.
 
 
 Bugfixes:

libyul/backends/evm/EVMCodeTransform.cpp

@@ -634,14 +634,34 @@ void CodeTransform::operator()(ForLoop const& _forLoop)
 	checkStackHeight(&_forLoop);
 }
 
-void CodeTransform::operator()(Break const&)
+int CodeTransform::appendPopUntil(int _targetDepth)
 {
-	yulAssert(false, "Code generation for break statement in Yul is not implemented yet.");
+	int const stackDiffAfter = m_assembly.stackHeight() - _targetDepth;
+	for (int i = 0; i < stackDiffAfter; ++i)
+		m_assembly.appendInstruction(solidity::Instruction::POP);
+	return stackDiffAfter;
+}
+
+void CodeTransform::operator()(Break const& _break)
+{
+	yulAssert(!m_context->forLoopStack.empty(), "Invalid break-statement. Requires surrounding for-loop in code generation.");
+	m_assembly.setSourceLocation(_break.location);
+
+	Context::JumpInfo const& jump = m_context->forLoopStack.top().done;
+	m_assembly.appendJumpTo(jump.label, appendPopUntil(jump.targetStackHeight));
+
+	checkStackHeight(&_break);
 }
 
-void CodeTransform::operator()(Continue const&)
+void CodeTransform::operator()(Continue const& _continue)
 {
-	yulAssert(false, "Code generation for continue statement in Yul is not implemented yet.");
+	yulAssert(!m_context->forLoopStack.empty(), "Invalid continue-statement. Requires surrounding for-loop in code generation.");
+	m_assembly.setSourceLocation(_continue.location);
+
+	Context::JumpInfo const& jump = m_context->forLoopStack.top().post;
+	m_assembly.appendJumpTo(jump.label, appendPopUntil(jump.targetStackHeight));
+
+	checkStackHeight(&_continue);
 }
 
 void CodeTransform::operator()(Block const& _block)

libyul/backends/evm/EVMCodeTransform.h

@@ -217,6 +217,10 @@ class CodeTransform: public boost::static_visitor<>
 	/// and corrects the stack height to the target stack height.
 	void stackError(StackTooDeepError _error, int _targetStackSize);
 
+	/// Ensures stack height is down to @p _targetDepth by appending POP instructions to the output assembly.
+	/// Returns the number of POP statements that have been appended.
+	int appendPopUntil(int _targetDepth);
+
 	AbstractAssembly& m_assembly;
 	AsmAnalysisInfo& m_info;
 	Scope* m_scope = nullptr;

test/libsolidity/semanticTests/for_loop_break.sol

@@ -0,0 +1,13 @@
+contract C {
+    function f() public returns (uint i) {
+        assembly {
+            for {} lt(i, 10) { i := add(i, 1) }
+            {
+                if eq(i, 6) { break }
+                i := add(i, 1)
+            }
+        }
+    }
+}
+// ----
+// f() -> 6

test/libsolidity/semanticTests/for_loop_continue.sol

@@ -0,0 +1,13 @@
+contract C {
+    function f() public returns (uint k) {
+        assembly {
+            for {let i := 0} lt(i, 10) { i := add(i, 1) }
+            {
+                if eq(mod(i, 2), 0) { continue }
+                k := add(k, 1)
+            }
+        }
+    }
+}
+// ----
+// f() -> 5