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CPP: Speed up OverflowStatic.ql #318

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Merged
merged 2 commits into from
Oct 26, 2018
Merged

CPP: Speed up OverflowStatic.ql #318

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6fc5ff5
CPP: Speed up getBufferSize.
geoffw0 Oct 12, 2018
a9b5553
CPP: Speed up phi_node > frontier_phi_node > ssa_defn recursion.
geoffw0 Oct 12, 2018
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10 changes: 6 additions & 4 deletions cpp/ql/src/semmle/code/cpp/commons/Buffer.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -81,19 +81,21 @@ int getBufferSize(Expr bufferExpr, Element why) {
// buffer is a fixed size dynamic allocation
isFixedSizeAllocationExpr(bufferExpr, result) and
why = bufferExpr
) or (
) or exists(DataFlow::ExprNode bufferExprNode |
// dataflow (all sources must be the same size)
bufferExprNode = DataFlow::exprNode(bufferExpr) and

result = min(Expr def |
DataFlow::localFlowStep(DataFlow::exprNode(def), DataFlow::exprNode(bufferExpr)) |
DataFlow::localFlowStep(DataFlow::exprNode(def), bufferExprNode) |
getBufferSize(def, _)
) and result = max(Expr def |
DataFlow::localFlowStep(DataFlow::exprNode(def), DataFlow::exprNode(bufferExpr)) |
DataFlow::localFlowStep(DataFlow::exprNode(def), bufferExprNode) |
getBufferSize(def, _)
) and

// find reason
exists(Expr def |
DataFlow::localFlowStep(DataFlow::exprNode(def), DataFlow::exprNode(bufferExpr)) |
DataFlow::localFlowStep(DataFlow::exprNode(def), bufferExprNode) |
why = def or
exists(getBufferSize(def, why))
)
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8 changes: 7 additions & 1 deletion cpp/ql/src/semmle/code/cpp/controlflow/SSAUtils.qll
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Expand Up @@ -124,11 +124,17 @@ cached library class SSAHelper extends int {
* Modern Compiler Implementation by Andrew Appel.
*/
private predicate frontier_phi_node(LocalScopeVariable v, BasicBlock b) {
exists(BasicBlock x | dominanceFrontier(x, b) and ssa_defn(v, _, x, _))
exists(BasicBlock x | dominanceFrontier(x, b) and ssa_defn_rec(v, x))
/* We can also eliminate those nodes where the variable is not live on any incoming edge */
and live_at_start_of_bb(v, b)
}

private predicate ssa_defn_rec(LocalScopeVariable v, BasicBlock b) {
phi_node(v, b)
or
variableUpdate(v, _, b, _)
}

/**
* Holds if `v` is defined, for the purpose of SSA, at `node`, which is at
* position `index` in block `b`. This includes definitions from phi nodes.
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