diff options
Diffstat (limited to 'libjulia')
| -rw-r--r-- | libjulia/optimiser/CommonSubexpressionEliminator.cpp | 30 | ||||
| -rw-r--r-- | libjulia/optimiser/README.md | 14 |
2 files changed, 40 insertions, 4 deletions
diff --git a/libjulia/optimiser/CommonSubexpressionEliminator.cpp b/libjulia/optimiser/CommonSubexpressionEliminator.cpp index 3122280b..458b3437 100644 --- a/libjulia/optimiser/CommonSubexpressionEliminator.cpp +++ b/libjulia/optimiser/CommonSubexpressionEliminator.cpp @@ -33,9 +33,31 @@ using namespace dev::julia; void CommonSubexpressionEliminator::visit(Expression& _e) { - // Single exception for substitution: We do not substitute one variable for another. - if (_e.type() != typeid(Identifier)) - // TODO this search rather inefficient. + // We visit the inner expression first to first simplify inner expressions, + // which hopefully allows more matches. + // Note that the DataFlowAnalyzer itself only has code for visiting Statements, + // so this basically invokes the AST walker directly and thus post-visiting + // is also fine with regards to data flow analysis. + DataFlowAnalyzer::visit(_e); + + if (_e.type() == typeid(Identifier)) + { + Identifier& identifier = boost::get<Identifier>(_e); + string const& name = identifier.name; + if (m_value.count(name)) + { + assertThrow(m_value.at(name), OptimizerException, ""); + if (m_value.at(name)->type() == typeid(Identifier)) + { + string const& value = boost::get<Identifier>(*m_value.at(name)).name; + if (inScope(value)) + _e = Identifier{locationOf(_e), value}; + } + } + } + else + { + // TODO this search is rather inefficient. for (auto const& var: m_value) { assertThrow(var.second, OptimizerException, ""); @@ -45,5 +67,5 @@ void CommonSubexpressionEliminator::visit(Expression& _e) break; } } - DataFlowAnalyzer::visit(_e); + } } diff --git a/libjulia/optimiser/README.md b/libjulia/optimiser/README.md index 4a50d5ca..faef818b 100644 --- a/libjulia/optimiser/README.md +++ b/libjulia/optimiser/README.md @@ -97,6 +97,20 @@ of any function call or opcode execution, the transformation is not performed. Note that the component will not move the assigned value of a variable assignment or a variable that is referenced more than once. +## Common Subexpression Eliminator + +This step replaces a subexpression by the value of a pre-existing variable +that currently has the same value (only if the value is movable), based +on a syntactic comparison. + +This can be used to compute a local value numbering, especially if the +expression splitter is used before. + +The expression simplifier will be able to perform better replacements +if the common subexpression eliminator was run right before it. + +Prerequisites: Disambiguator + ## Full Function Inliner ## Rematerialisation |