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This is to support some analyses, like -Wunreachable-code, that will need to recover the original unprunned CFG edges in order to suppress issues that aren't really bugs in practice. There are two important changes here: - AdjacentBlock replaces CFGBlock* for CFG successors/predecessors. This has the size of 2 pointers, instead of 1. This is unlikely to have a significant memory impact on Sema since a single CFG usually exists at one time, but could impact the memory usage of the static analyzer. This could possibly be optimized down to a single pointer with some cleverness. - Predecessors can now contain null predecessors, which means some analyses doing a reverse traversal will need to take into account. This already exists for successors, which contain successor slots for specific branch kinds (e.g., 'if') that expect a fixed number of successors, even if a branch is not reachable. llvm-svn: 202325
77 lines
2.5 KiB
C++
77 lines
2.5 KiB
C++
//==- CFGReachabilityAnalysis.cpp - Basic reachability analysis --*- C++ -*-==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines a flow-sensitive, (mostly) path-insensitive reachability
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// analysis based on Clang's CFGs. Clients can query if a given basic block
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// is reachable within the CFG.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/SmallVector.h"
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#include "clang/Analysis/Analyses/CFGReachabilityAnalysis.h"
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#include "clang/Analysis/CFG.h"
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using namespace clang;
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CFGReverseBlockReachabilityAnalysis::CFGReverseBlockReachabilityAnalysis(const CFG &cfg)
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: analyzed(cfg.getNumBlockIDs(), false) {}
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bool CFGReverseBlockReachabilityAnalysis::isReachable(const CFGBlock *Src,
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const CFGBlock *Dst) {
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const unsigned DstBlockID = Dst->getBlockID();
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// If we haven't analyzed the destination node, run the analysis now
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if (!analyzed[DstBlockID]) {
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mapReachability(Dst);
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analyzed[DstBlockID] = true;
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}
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// Return the cached result
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return reachable[DstBlockID][Src->getBlockID()];
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}
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// Maps reachability to a common node by walking the predecessors of the
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// destination node.
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void CFGReverseBlockReachabilityAnalysis::mapReachability(const CFGBlock *Dst) {
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SmallVector<const CFGBlock *, 11> worklist;
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llvm::BitVector visited(analyzed.size());
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ReachableSet &DstReachability = reachable[Dst->getBlockID()];
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DstReachability.resize(analyzed.size(), false);
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// Start searching from the destination node, since we commonly will perform
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// multiple queries relating to a destination node.
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worklist.push_back(Dst);
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bool firstRun = true;
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while (!worklist.empty()) {
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const CFGBlock *block = worklist.pop_back_val();
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if (visited[block->getBlockID()])
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continue;
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visited[block->getBlockID()] = true;
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// Update reachability information for this node -> Dst
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if (!firstRun) {
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// Don't insert Dst -> Dst unless it was a predecessor of itself
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DstReachability[block->getBlockID()] = true;
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}
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else
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firstRun = false;
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// Add the predecessors to the worklist.
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for (CFGBlock::const_pred_iterator i = block->pred_begin(),
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e = block->pred_end(); i != e; ++i) {
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if (*i)
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worklist.push_back(*i);
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}
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}
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}
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