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-rw-r--r--libjulia/optimiser/UnusedPruner.cpp7
-rw-r--r--libjulia/optimiser/UnusedPruner.h2
2 files changed, 9 insertions, 0 deletions
diff --git a/libjulia/optimiser/UnusedPruner.cpp b/libjulia/optimiser/UnusedPruner.cpp
index 50f4d9f1..50038431 100644
--- a/libjulia/optimiser/UnusedPruner.cpp
+++ b/libjulia/optimiser/UnusedPruner.cpp
@@ -55,6 +55,11 @@ void UnusedPruner::operator()(Block& _block)
else if (statement.type() == typeid(VariableDeclaration))
{
VariableDeclaration& varDecl = boost::get<VariableDeclaration>(statement);
+ // Multi-variable declarations are special. We can only remove it
+ // if all vairables are unused and the right-hand-side is either
+ // movable or it return a single value. In the latter case, we
+ // replace `let a := f()` by `pop(f())` (in pure IULIA, this will be
+ // `drop(f())`).
if (boost::algorithm::none_of(
varDecl.variables,
[=](TypedName const& _typedName) { return used(_typedName.name); }
@@ -68,6 +73,8 @@ void UnusedPruner::operator()(Block& _block)
statement = Block{std::move(varDecl.location), {}};
}
else if (varDecl.variables.size() == 1)
+ // In pure IULIA, this should be replaced by a function call to `drop`
+ // instead of `pop`.
statement = ExpressionStatement{varDecl.location, FunctionalInstruction{
varDecl.location,
solidity::Instruction::POP,
diff --git a/libjulia/optimiser/UnusedPruner.h b/libjulia/optimiser/UnusedPruner.h
index 8b521232..73e8de7c 100644
--- a/libjulia/optimiser/UnusedPruner.h
+++ b/libjulia/optimiser/UnusedPruner.h
@@ -49,8 +49,10 @@ public:
using ASTModifier::operator();
virtual void operator()(Block& _block) override;
+ // @returns true iff the code changed in the previous run.
bool shouldRunAgain() const { return m_shouldRunAgain; }
+ // Run the pruner until the code does not change anymore.
static void runUntilStabilised(Block& _ast);
private: