Feature/variable renaming #38
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mateusluizfb
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Mar 23, 2021
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| map[&T, set[&T]] dominanceTree = createDominanceTree(flowGraph); | ||
| map[&T, set[&T]] dominanceFrontier = createDominanceFrontier(flowGraph, dominanceTree); | ||
| FlowGraph phiFunctionFlowGraph = insertPhiFunctions(flowGraph, dominanceFrontier); | ||
| result = applyVariableRenaming(phiFunctionFlowGraph); |
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Applies each SSA's stages
mateusluizfb
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| public FlowGraph insertPhiFunctions(FlowGraph flowGraph, map[&T, set[&T]] dominanceFrontier) { | ||
| newFlowGraph = { <origin, destination> | <origin, destination> <- flowGraph }; | ||
| variableList = { getStmtVariable(graphNode) | <graphNode, _> <- flowGraph, isVariable(graphNode) }; | ||
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| for(Variable variable <- variableList) { | ||
| F = {}; // set of basic blocks where φ is added | ||
| W = {}; // set of basic blocks that contain definitions of v | ||
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| for(variableNode <- blocksWithVariable(flowGraph, variable)) { // d ∈ Defs(v) | ||
| B = variableNode; | ||
| W = W + {B}; | ||
| }; | ||
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| while(size(W) != 0) { | ||
| // remove a basic block X from W | ||
| tuple[Node, set[Node]] elements = takeOneFrom(W); | ||
| X = elements[0]; | ||
| W = elements[1]; | ||
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| if(X in dominanceFrontier) { // Avoids NoSuchKey error | ||
| frontierNodes = dominanceFrontier[X]; | ||
| for(Y <- frontierNodes) { // Y : basic block ∈ DF(X ) | ||
| if(size({Y} & F) == 0 && isJoinNode(flowGraph, Y)) { // Y \notin F && Y is a join node | ||
| newFlowGraph = insertPhiFunction(newFlowGraph, Y, variable); // add v←φ(...) at entry of Y | ||
| F = F + {Y}; // F ← F ∪ {Y} | ||
| if(size([Y] & blocksWithVariable(flowGraph, variable)) == 0) { // Y \notin Defs(v) | ||
| W = W + {Y}; // W ←W ∪{Y} | ||
| }; | ||
| }; | ||
| }; | ||
| }; | ||
| }; | ||
| }; | ||
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| return newFlowGraph; | ||
| } |
mateusluizfb
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Mar 23, 2021
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| public FlowGraph applyVariableRenaming(FlowGraph flowGraph) { | ||
| VARIABLE_VERSION_STACK = (); // Stack for each variable that holds the next variable to ve replaced | ||
| VARIABLE_ASSIGNMENT_COUNT = (); // Counts how many assingments have been processed for a given variable | ||
| REPLACED_NODES = {}; // Keep tracking of all nodes replaced in one execution | ||
| LAST_VERSION_REPLACED = (); // Keep tracking of the new version of a given node | ||
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| ADJACENCIES_MATRIX = createAdjacenciesMatrix(flowGraph); // Mainly used to rebuild the renamed flow graph | ||
| IDOM_TREE = createIdomTree(createDominanceTree(flowGraph)); // Used to traverse the flow graph | ||
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| map[Node, list[Node]] newBlockTree = replace(entryNode()); // Start algorithm | ||
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| // Rebuild renamed flowGraph | ||
| FlowGraph newFlowGraph = {}; | ||
| for(fatherNode <- newBlockTree) { | ||
| newFlowGraph = newFlowGraph + { <fatherNode, nodeChild> | nodeChild <- ADJACENCIES_MATRIX[fatherNode]}; | ||
| }; | ||
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| return newFlowGraph; | ||
| } | ||
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| public map[Node, list[Node]] replace(Node X) { | ||
| if((X == exitNode())) return ADJACENCIES_MATRIX; | ||
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| Node oldNode = X; | ||
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| // Deal with all nodes that aren't assigments bug uses a variable in some way | ||
| if(isNonAssignmentStatementToRename(X)) { | ||
| stmtNode(statement) = X; | ||
| Node renamedStatement = stmtNode(replaceImmediateUse(statement)); | ||
| renameNodeOcurrecies(X, renamedStatement); | ||
| X = renamedStatement; | ||
| }; | ||
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| // Deal will all nodes that are an assigment and are not renamed | ||
| if(isOrdinaryAssignment(X) && !isRenamed(X)) { | ||
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| // Replace right hand side variables | ||
| list[Immediate] rightHandNodeImmediates = getRightHandSideImmediates(X); | ||
| for(rightHandSideImmediate <- rightHandNodeImmediates) { | ||
| newAssignStmt = replaceRightVariableVersion(ADJACENCIES_MATRIX, rightHandSideImmediate, X); | ||
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| renameNodeOcurrecies(X, newAssignStmt); | ||
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| X = newAssignStmt; | ||
| }; | ||
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| // Replace left hand side variables | ||
| if(isLeftHandSideVariable(X)) { | ||
| Variable V = getStmtVariable(X); | ||
| Immediate localVariableImmediate = local(V[0]); | ||
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| int assingmentQuantity = returnAssignmentQuantity(localVariableImmediate); | ||
| newAssignStmt = replaceLeftVariableVersion(ADJACENCIES_MATRIX, X, assingmentQuantity); | ||
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| renameNodeOcurrecies(X, newAssignStmt); | ||
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| stackVariableVersion(localVariableImmediate, assingmentQuantity); | ||
| iterateAssignmentQuantity(localVariableImmediate); | ||
| findAndAddPhiFunctionArgs(oldNode, newAssignStmt); // Search variable uses of replaced variable in phi-function and rename it | ||
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| X = newAssignStmt; | ||
| }; | ||
| } | ||
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| for(child <- IDOM_TREE[X]) { | ||
| // We need to check the last version replaced because the renamed version was not beign reflected in the current `for` statement iteration, | ||
| // so we need to check the last version replaced | ||
| nodeToRename = LAST_VERSION_REPLACED[child]? ? LAST_VERSION_REPLACED[child] : child; | ||
| replace(nodeToRename); | ||
| }; | ||
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| if(!ignoreNode(oldNode) && isVariable(oldNode) && !isRenamed(X)) | ||
| popOldNode(oldNode); | ||
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| return ADJACENCIES_MATRIX; | ||
| } |
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This is the largest module and the most messy one, but try to mimic the Cytron's algorithm:
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This reverts commit 6267bbc.
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This is a direct implementation of Cytron's Single Static Assignment Form. The code also uses some ideas and algorithms presented by the SSA book.
The implementation ignores two types of instructions:
invokeStmtassign(fieldRef(_, _), _)The code is composed into five main modules:
lang::jimple::toolkit::ssa::Generatoris responsible to call all the other modules to perform a complete SSA transformation, also validates if the ignored instructions are present;lang::jimple::toolkit::ssa::DominanceFrontieris responsible to create the graph's dominance frontier;lang::jimple::toolkit::ssa::DominanceTreeis responsible to create the graph's dominance tree;lang::jimple::toolkit::ssa::PhiFunctionInsertionit inserts the phi functions in the graph;lang::jimple::toolkit::ssa::VariableRenamingit renames all the variables for different versions;