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1df9859c40
and T->isPointerTy(). Convert most instances of the first form to the second form. Requested by Chris. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96344 91177308-0d34-0410-b5e6-96231b3b80d8
1118 lines
38 KiB
C++
1118 lines
38 KiB
C++
//===------- ABCD.cpp - Removes redundant conditional branches ------------===//
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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 pass removes redundant branch instructions. This algorithm was
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// described by Rastislav Bodik, Rajiv Gupta and Vivek Sarkar in their paper
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// "ABCD: Eliminating Array Bounds Checks on Demand (2000)". The original
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// Algorithm was created to remove array bound checks for strongly typed
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// languages. This implementation expands the idea and removes any conditional
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// branches that can be proved redundant, not only those used in array bound
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// checks. With the SSI representation, each variable has a
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// constraint. By analyzing these constraints we can prove that a branch is
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// redundant. When a branch is proved redundant it means that
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// one direction will always be taken; thus, we can change this branch into an
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// unconditional jump.
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// It is advisable to run SimplifyCFG and Aggressive Dead Code Elimination
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// after ABCD to clean up the code.
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// This implementation was created based on the implementation of the ABCD
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// algorithm implemented for the compiler Jitrino.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "abcd"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Constants.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/SSI.h"
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using namespace llvm;
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STATISTIC(NumBranchTested, "Number of conditional branches analyzed");
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STATISTIC(NumBranchRemoved, "Number of conditional branches removed");
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namespace {
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class ABCD : public FunctionPass {
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public:
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static char ID; // Pass identification, replacement for typeid.
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ABCD() : FunctionPass(&ID) {}
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<SSI>();
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}
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bool runOnFunction(Function &F);
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private:
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/// Keep track of whether we've modified the program yet.
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bool modified;
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enum ProveResult {
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False = 0,
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Reduced = 1,
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True = 2
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};
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typedef ProveResult (*meet_function)(ProveResult, ProveResult);
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static ProveResult max(ProveResult res1, ProveResult res2) {
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return (ProveResult) std::max(res1, res2);
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}
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static ProveResult min(ProveResult res1, ProveResult res2) {
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return (ProveResult) std::min(res1, res2);
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}
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class Bound {
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public:
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Bound(APInt v, bool upper) : value(v), upper_bound(upper) {}
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Bound(const Bound *b, int cnst)
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: value(b->value - cnst), upper_bound(b->upper_bound) {}
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Bound(const Bound *b, const APInt &cnst)
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: value(b->value - cnst), upper_bound(b->upper_bound) {}
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/// Test if Bound is an upper bound
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bool isUpperBound() const { return upper_bound; }
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/// Get the bitwidth of this bound
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int32_t getBitWidth() const { return value.getBitWidth(); }
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/// Creates a Bound incrementing the one received
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static Bound *createIncrement(const Bound *b) {
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return new Bound(b->isUpperBound() ? b->value+1 : b->value-1,
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b->upper_bound);
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}
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/// Creates a Bound decrementing the one received
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static Bound *createDecrement(const Bound *b) {
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return new Bound(b->isUpperBound() ? b->value-1 : b->value+1,
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b->upper_bound);
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}
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/// Test if two bounds are equal
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static bool eq(const Bound *a, const Bound *b) {
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if (!a || !b) return false;
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assert(a->isUpperBound() == b->isUpperBound());
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return a->value == b->value;
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}
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/// Test if val is less than or equal to Bound b
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static bool leq(APInt val, const Bound *b) {
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if (!b) return false;
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return b->isUpperBound() ? val.sle(b->value) : val.sge(b->value);
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}
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/// Test if Bound a is less then or equal to Bound
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static bool leq(const Bound *a, const Bound *b) {
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if (!a || !b) return false;
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assert(a->isUpperBound() == b->isUpperBound());
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return a->isUpperBound() ? a->value.sle(b->value) :
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a->value.sge(b->value);
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}
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/// Test if Bound a is less then Bound b
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static bool lt(const Bound *a, const Bound *b) {
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if (!a || !b) return false;
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assert(a->isUpperBound() == b->isUpperBound());
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return a->isUpperBound() ? a->value.slt(b->value) :
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a->value.sgt(b->value);
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}
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/// Test if Bound b is greater then or equal val
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static bool geq(const Bound *b, APInt val) {
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return leq(val, b);
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}
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/// Test if Bound a is greater then or equal Bound b
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static bool geq(const Bound *a, const Bound *b) {
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return leq(b, a);
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}
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private:
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APInt value;
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bool upper_bound;
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};
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/// This class is used to store results some parts of the graph,
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/// so information does not need to be recalculated. The maximum false,
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/// minimum true and minimum reduced results are stored
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class MemoizedResultChart {
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public:
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MemoizedResultChart()
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: max_false(NULL), min_true(NULL), min_reduced(NULL) {}
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/// Returns the max false
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Bound *getFalse() const { return max_false; }
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/// Returns the min true
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Bound *getTrue() const { return min_true; }
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/// Returns the min reduced
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Bound *getReduced() const { return min_reduced; }
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/// Return the stored result for this bound
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ProveResult getResult(const Bound *bound) const;
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/// Stores a false found
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void addFalse(Bound *bound);
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/// Stores a true found
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void addTrue(Bound *bound);
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/// Stores a Reduced found
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void addReduced(Bound *bound);
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/// Clears redundant reduced
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/// If a min_true is smaller than a min_reduced then the min_reduced
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/// is unnecessary and then removed. It also works for min_reduced
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/// begin smaller than max_false.
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void clearRedundantReduced();
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void clear() {
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delete max_false;
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delete min_true;
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delete min_reduced;
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}
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private:
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Bound *max_false, *min_true, *min_reduced;
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};
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/// This class stores the result found for a node of the graph,
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/// so these results do not need to be recalculated, only searched for.
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class MemoizedResult {
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public:
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/// Test if there is true result stored from b to a
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/// that is less then the bound
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bool hasTrue(Value *b, const Bound *bound) const {
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Bound *trueBound = map.lookup(b).getTrue();
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return trueBound && Bound::leq(trueBound, bound);
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}
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/// Test if there is false result stored from b to a
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/// that is less then the bound
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bool hasFalse(Value *b, const Bound *bound) const {
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Bound *falseBound = map.lookup(b).getFalse();
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return falseBound && Bound::leq(falseBound, bound);
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}
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/// Test if there is reduced result stored from b to a
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/// that is less then the bound
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bool hasReduced(Value *b, const Bound *bound) const {
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Bound *reducedBound = map.lookup(b).getReduced();
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return reducedBound && Bound::leq(reducedBound, bound);
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}
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/// Returns the stored bound for b
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ProveResult getBoundResult(Value *b, Bound *bound) {
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return map[b].getResult(bound);
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}
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/// Clears the map
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void clear() {
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DenseMapIterator<Value*, MemoizedResultChart> begin = map.begin();
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DenseMapIterator<Value*, MemoizedResultChart> end = map.end();
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for (; begin != end; ++begin) {
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begin->second.clear();
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}
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map.clear();
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}
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/// Stores the bound found
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void updateBound(Value *b, Bound *bound, const ProveResult res);
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private:
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// Maps a nod in the graph with its results found.
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DenseMap<Value*, MemoizedResultChart> map;
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};
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/// This class represents an edge in the inequality graph used by the
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/// ABCD algorithm. An edge connects node v to node u with a value c if
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/// we could infer a constraint v <= u + c in the source program.
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class Edge {
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public:
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Edge(Value *V, APInt val, bool upper)
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: vertex(V), value(val), upper_bound(upper) {}
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Value *getVertex() const { return vertex; }
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const APInt &getValue() const { return value; }
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bool isUpperBound() const { return upper_bound; }
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private:
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Value *vertex;
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APInt value;
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bool upper_bound;
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};
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/// Weighted and Directed graph to represent constraints.
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/// There is one type of constraint, a <= b + X, which will generate an
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/// edge from b to a with weight X.
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class InequalityGraph {
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public:
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/// Adds an edge from V_from to V_to with weight value
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void addEdge(Value *V_from, Value *V_to, APInt value, bool upper);
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/// Test if there is a node V
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bool hasNode(Value *V) const { return graph.count(V); }
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/// Test if there is any edge from V in the upper direction
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bool hasEdge(Value *V, bool upper) const;
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/// Returns all edges pointed by vertex V
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SmallPtrSet<Edge *, 16> getEdges(Value *V) const {
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return graph.lookup(V);
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}
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/// Prints the graph in dot format.
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/// Blue edges represent upper bound and Red lower bound.
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void printGraph(raw_ostream &OS, Function &F) const {
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printHeader(OS, F);
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printBody(OS);
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printFooter(OS);
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}
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/// Clear the graph
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void clear() {
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graph.clear();
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}
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private:
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DenseMap<Value *, SmallPtrSet<Edge *, 16> > graph;
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/// Adds a Node to the graph.
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DenseMap<Value *, SmallPtrSet<Edge *, 16> >::iterator addNode(Value *V) {
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SmallPtrSet<Edge *, 16> p;
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return graph.insert(std::make_pair(V, p)).first;
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}
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/// Prints the header of the dot file
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void printHeader(raw_ostream &OS, Function &F) const;
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/// Prints the footer of the dot file
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void printFooter(raw_ostream &OS) const {
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OS << "}\n";
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}
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/// Prints the body of the dot file
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void printBody(raw_ostream &OS) const;
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/// Prints vertex source to the dot file
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void printVertex(raw_ostream &OS, Value *source) const;
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/// Prints the edge to the dot file
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void printEdge(raw_ostream &OS, Value *source, Edge *edge) const;
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void printName(raw_ostream &OS, Value *info) const;
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};
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/// Iterates through all BasicBlocks, if the Terminator Instruction
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/// uses an Comparator Instruction, all operands of this comparator
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/// are sent to be transformed to SSI. Only Instruction operands are
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/// transformed.
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void createSSI(Function &F);
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/// Creates the graphs for this function.
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/// It will look for all comparators used in branches, and create them.
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/// These comparators will create constraints for any instruction as an
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/// operand.
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void executeABCD(Function &F);
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/// Seeks redundancies in the comparator instruction CI.
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/// If the ABCD algorithm can prove that the comparator CI always
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/// takes one way, then the Terminator Instruction TI is substituted from
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/// a conditional branch to a unconditional one.
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/// This code basically receives a comparator, and verifies which kind of
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/// instruction it is. Depending on the kind of instruction, we use different
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/// strategies to prove its redundancy.
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void seekRedundancy(ICmpInst *ICI, TerminatorInst *TI);
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/// Substitutes Terminator Instruction TI, that is a conditional branch,
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/// with one unconditional branch. Succ_edge determines if the new
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/// unconditional edge will be the first or second edge of the former TI
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/// instruction.
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void removeRedundancy(TerminatorInst *TI, bool Succ_edge);
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/// When an conditional branch is removed, the BasicBlock that is no longer
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/// reachable will have problems in phi functions. This method fixes these
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/// phis removing the former BasicBlock from the list of incoming BasicBlocks
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/// of all phis. In case the phi remains with no predecessor it will be
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/// marked to be removed later.
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void fixPhi(BasicBlock *BB, BasicBlock *Succ);
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/// Removes phis that have no predecessor
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void removePhis();
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/// Creates constraints for Instructions.
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/// If the constraint for this instruction has already been created
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/// nothing is done.
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void createConstraintInstruction(Instruction *I);
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/// Creates constraints for Binary Operators.
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/// It will create constraints only for addition and subtraction,
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/// the other binary operations are not treated by ABCD.
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/// For additions in the form a = b + X and a = X + b, where X is a constant,
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/// the constraint a <= b + X can be obtained. For this constraint, an edge
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/// a->b with weight X is added to the lower bound graph, and an edge
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/// b->a with weight -X is added to the upper bound graph.
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/// Only subtractions in the format a = b - X is used by ABCD.
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/// Edges are created using the same semantic as addition.
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void createConstraintBinaryOperator(BinaryOperator *BO);
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/// Creates constraints for Comparator Instructions.
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/// Only comparators that have any of the following operators
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/// are used to create constraints: >=, >, <=, <. And only if
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/// at least one operand is an Instruction. In a Comparator Instruction
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/// a op b, there will be 4 sigma functions a_t, a_f, b_t and b_f. Where
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/// t and f represent sigma for operands in true and false branches. The
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/// following constraints can be obtained. a_t <= a, a_f <= a, b_t <= b and
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/// b_f <= b. There are two more constraints that depend on the operator.
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/// For the operator <= : a_t <= b_t and b_f <= a_f-1
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/// For the operator < : a_t <= b_t-1 and b_f <= a_f
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/// For the operator >= : b_t <= a_t and a_f <= b_f-1
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/// For the operator > : b_t <= a_t-1 and a_f <= b_f
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void createConstraintCmpInst(ICmpInst *ICI, TerminatorInst *TI);
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/// Creates constraints for PHI nodes.
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/// In a PHI node a = phi(b,c) we can create the constraint
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/// a<= max(b,c). With this constraint there will be the edges,
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/// b->a and c->a with weight 0 in the lower bound graph, and the edges
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/// a->b and a->c with weight 0 in the upper bound graph.
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void createConstraintPHINode(PHINode *PN);
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/// Given a binary operator, we are only interest in the case
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/// that one operand is an Instruction and the other is a ConstantInt. In
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/// this case the method returns true, otherwise false. It also obtains the
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/// Instruction and ConstantInt from the BinaryOperator and returns it.
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bool createBinaryOperatorInfo(BinaryOperator *BO, Instruction **I1,
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Instruction **I2, ConstantInt **C1,
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ConstantInt **C2);
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/// This method creates a constraint between a Sigma and an Instruction.
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/// These constraints are created as soon as we find a comparator that uses a
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/// SSI variable.
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void createConstraintSigInst(Instruction *I_op, BasicBlock *BB_succ_t,
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BasicBlock *BB_succ_f, PHINode **SIG_op_t,
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PHINode **SIG_op_f);
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/// If PN_op1 and PN_o2 are different from NULL, create a constraint
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/// PN_op2 -> PN_op1 with value. In case any of them is NULL, replace
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/// with the respective V_op#, if V_op# is a ConstantInt.
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void createConstraintSigSig(PHINode *SIG_op1, PHINode *SIG_op2,
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ConstantInt *V_op1, ConstantInt *V_op2,
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APInt value);
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/// Returns the sigma representing the Instruction I in BasicBlock BB.
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/// Returns NULL in case there is no sigma for this Instruction in this
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/// Basic Block. This methods assume that sigmas are the first instructions
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/// in a block, and that there can be only two sigmas in a block. So it will
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/// only look on the first two instructions of BasicBlock BB.
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PHINode *findSigma(BasicBlock *BB, Instruction *I);
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/// Original ABCD algorithm to prove redundant checks.
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/// This implementation works on any kind of inequality branch.
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bool demandProve(Value *a, Value *b, int c, bool upper_bound);
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/// Prove that distance between b and a is <= bound
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ProveResult prove(Value *a, Value *b, Bound *bound, unsigned level);
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/// Updates the distance value for a and b
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void updateMemDistance(Value *a, Value *b, Bound *bound, unsigned level,
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meet_function meet);
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InequalityGraph inequality_graph;
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MemoizedResult mem_result;
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DenseMap<Value*, Bound*> active;
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SmallPtrSet<Value*, 16> created;
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SmallVector<PHINode *, 16> phis_to_remove;
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};
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} // end anonymous namespace.
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char ABCD::ID = 0;
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static RegisterPass<ABCD> X("abcd", "ABCD: Eliminating Array Bounds Checks on Demand");
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bool ABCD::runOnFunction(Function &F) {
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modified = false;
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createSSI(F);
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executeABCD(F);
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DEBUG(inequality_graph.printGraph(dbgs(), F));
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removePhis();
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inequality_graph.clear();
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mem_result.clear();
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active.clear();
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created.clear();
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phis_to_remove.clear();
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return modified;
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}
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/// Iterates through all BasicBlocks, if the Terminator Instruction
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/// uses an Comparator Instruction, all operands of this comparator
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/// are sent to be transformed to SSI. Only Instruction operands are
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/// transformed.
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void ABCD::createSSI(Function &F) {
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SSI *ssi = &getAnalysis<SSI>();
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SmallVector<Instruction *, 16> Insts;
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for (Function::iterator begin = F.begin(), end = F.end();
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begin != end; ++begin) {
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BasicBlock *BB = begin;
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TerminatorInst *TI = BB->getTerminator();
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if (TI->getNumOperands() == 0)
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continue;
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if (ICmpInst *ICI = dyn_cast<ICmpInst>(TI->getOperand(0))) {
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if (Instruction *I = dyn_cast<Instruction>(ICI->getOperand(0))) {
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modified = true; // XXX: but yet createSSI might do nothing
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Insts.push_back(I);
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}
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if (Instruction *I = dyn_cast<Instruction>(ICI->getOperand(1))) {
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modified = true;
|
|
Insts.push_back(I);
|
|
}
|
|
}
|
|
}
|
|
ssi->createSSI(Insts);
|
|
}
|
|
|
|
/// Creates the graphs for this function.
|
|
/// It will look for all comparators used in branches, and create them.
|
|
/// These comparators will create constraints for any instruction as an
|
|
/// operand.
|
|
void ABCD::executeABCD(Function &F) {
|
|
for (Function::iterator begin = F.begin(), end = F.end();
|
|
begin != end; ++begin) {
|
|
BasicBlock *BB = begin;
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
if (TI->getNumOperands() == 0)
|
|
continue;
|
|
|
|
ICmpInst *ICI = dyn_cast<ICmpInst>(TI->getOperand(0));
|
|
if (!ICI || !ICI->getOperand(0)->getType()->isIntegerTy())
|
|
continue;
|
|
|
|
createConstraintCmpInst(ICI, TI);
|
|
seekRedundancy(ICI, TI);
|
|
}
|
|
}
|
|
|
|
/// Seeks redundancies in the comparator instruction CI.
|
|
/// If the ABCD algorithm can prove that the comparator CI always
|
|
/// takes one way, then the Terminator Instruction TI is substituted from
|
|
/// a conditional branch to a unconditional one.
|
|
/// This code basically receives a comparator, and verifies which kind of
|
|
/// instruction it is. Depending on the kind of instruction, we use different
|
|
/// strategies to prove its redundancy.
|
|
void ABCD::seekRedundancy(ICmpInst *ICI, TerminatorInst *TI) {
|
|
CmpInst::Predicate Pred = ICI->getPredicate();
|
|
|
|
Value *source, *dest;
|
|
int distance1, distance2;
|
|
bool upper;
|
|
|
|
switch(Pred) {
|
|
case CmpInst::ICMP_SGT: // signed greater than
|
|
upper = false;
|
|
distance1 = 1;
|
|
distance2 = 0;
|
|
break;
|
|
|
|
case CmpInst::ICMP_SGE: // signed greater or equal
|
|
upper = false;
|
|
distance1 = 0;
|
|
distance2 = -1;
|
|
break;
|
|
|
|
case CmpInst::ICMP_SLT: // signed less than
|
|
upper = true;
|
|
distance1 = -1;
|
|
distance2 = 0;
|
|
break;
|
|
|
|
case CmpInst::ICMP_SLE: // signed less or equal
|
|
upper = true;
|
|
distance1 = 0;
|
|
distance2 = 1;
|
|
break;
|
|
|
|
default:
|
|
return;
|
|
}
|
|
|
|
++NumBranchTested;
|
|
source = ICI->getOperand(0);
|
|
dest = ICI->getOperand(1);
|
|
if (demandProve(dest, source, distance1, upper)) {
|
|
removeRedundancy(TI, true);
|
|
} else if (demandProve(dest, source, distance2, !upper)) {
|
|
removeRedundancy(TI, false);
|
|
}
|
|
}
|
|
|
|
/// Substitutes Terminator Instruction TI, that is a conditional branch,
|
|
/// with one unconditional branch. Succ_edge determines if the new
|
|
/// unconditional edge will be the first or second edge of the former TI
|
|
/// instruction.
|
|
void ABCD::removeRedundancy(TerminatorInst *TI, bool Succ_edge) {
|
|
BasicBlock *Succ;
|
|
if (Succ_edge) {
|
|
Succ = TI->getSuccessor(0);
|
|
fixPhi(TI->getParent(), TI->getSuccessor(1));
|
|
} else {
|
|
Succ = TI->getSuccessor(1);
|
|
fixPhi(TI->getParent(), TI->getSuccessor(0));
|
|
}
|
|
|
|
BranchInst::Create(Succ, TI);
|
|
TI->eraseFromParent(); // XXX: invoke
|
|
++NumBranchRemoved;
|
|
modified = true;
|
|
}
|
|
|
|
/// When an conditional branch is removed, the BasicBlock that is no longer
|
|
/// reachable will have problems in phi functions. This method fixes these
|
|
/// phis removing the former BasicBlock from the list of incoming BasicBlocks
|
|
/// of all phis. In case the phi remains with no predecessor it will be
|
|
/// marked to be removed later.
|
|
void ABCD::fixPhi(BasicBlock *BB, BasicBlock *Succ) {
|
|
BasicBlock::iterator begin = Succ->begin();
|
|
while (PHINode *PN = dyn_cast<PHINode>(begin++)) {
|
|
PN->removeIncomingValue(BB, false);
|
|
if (PN->getNumIncomingValues() == 0)
|
|
phis_to_remove.push_back(PN);
|
|
}
|
|
}
|
|
|
|
/// Removes phis that have no predecessor
|
|
void ABCD::removePhis() {
|
|
for (unsigned i = 0, e = phis_to_remove.size(); i != e; ++i) {
|
|
PHINode *PN = phis_to_remove[i];
|
|
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
|
|
PN->eraseFromParent();
|
|
}
|
|
}
|
|
|
|
/// Creates constraints for Instructions.
|
|
/// If the constraint for this instruction has already been created
|
|
/// nothing is done.
|
|
void ABCD::createConstraintInstruction(Instruction *I) {
|
|
// Test if this instruction has not been created before
|
|
if (created.insert(I)) {
|
|
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
|
|
createConstraintBinaryOperator(BO);
|
|
} else if (PHINode *PN = dyn_cast<PHINode>(I)) {
|
|
createConstraintPHINode(PN);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Creates constraints for Binary Operators.
|
|
/// It will create constraints only for addition and subtraction,
|
|
/// the other binary operations are not treated by ABCD.
|
|
/// For additions in the form a = b + X and a = X + b, where X is a constant,
|
|
/// the constraint a <= b + X can be obtained. For this constraint, an edge
|
|
/// a->b with weight X is added to the lower bound graph, and an edge
|
|
/// b->a with weight -X is added to the upper bound graph.
|
|
/// Only subtractions in the format a = b - X is used by ABCD.
|
|
/// Edges are created using the same semantic as addition.
|
|
void ABCD::createConstraintBinaryOperator(BinaryOperator *BO) {
|
|
Instruction *I1 = NULL, *I2 = NULL;
|
|
ConstantInt *CI1 = NULL, *CI2 = NULL;
|
|
|
|
// Test if an operand is an Instruction and the other is a Constant
|
|
if (!createBinaryOperatorInfo(BO, &I1, &I2, &CI1, &CI2))
|
|
return;
|
|
|
|
Instruction *I = 0;
|
|
APInt value;
|
|
|
|
switch (BO->getOpcode()) {
|
|
case Instruction::Add:
|
|
if (I1) {
|
|
I = I1;
|
|
value = CI2->getValue();
|
|
} else if (I2) {
|
|
I = I2;
|
|
value = CI1->getValue();
|
|
}
|
|
break;
|
|
|
|
case Instruction::Sub:
|
|
// Instructions like a = X-b, where X is a constant are not represented
|
|
// in the graph.
|
|
if (!I1)
|
|
return;
|
|
|
|
I = I1;
|
|
value = -CI2->getValue();
|
|
break;
|
|
|
|
default:
|
|
return;
|
|
}
|
|
|
|
inequality_graph.addEdge(I, BO, value, true);
|
|
inequality_graph.addEdge(BO, I, -value, false);
|
|
createConstraintInstruction(I);
|
|
}
|
|
|
|
/// Given a binary operator, we are only interest in the case
|
|
/// that one operand is an Instruction and the other is a ConstantInt. In
|
|
/// this case the method returns true, otherwise false. It also obtains the
|
|
/// Instruction and ConstantInt from the BinaryOperator and returns it.
|
|
bool ABCD::createBinaryOperatorInfo(BinaryOperator *BO, Instruction **I1,
|
|
Instruction **I2, ConstantInt **C1,
|
|
ConstantInt **C2) {
|
|
Value *op1 = BO->getOperand(0);
|
|
Value *op2 = BO->getOperand(1);
|
|
|
|
if ((*I1 = dyn_cast<Instruction>(op1))) {
|
|
if ((*C2 = dyn_cast<ConstantInt>(op2)))
|
|
return true; // First is Instruction and second ConstantInt
|
|
|
|
return false; // Both are Instruction
|
|
} else {
|
|
if ((*C1 = dyn_cast<ConstantInt>(op1)) &&
|
|
(*I2 = dyn_cast<Instruction>(op2)))
|
|
return true; // First is ConstantInt and second Instruction
|
|
|
|
return false; // Both are not Instruction
|
|
}
|
|
}
|
|
|
|
/// Creates constraints for Comparator Instructions.
|
|
/// Only comparators that have any of the following operators
|
|
/// are used to create constraints: >=, >, <=, <. And only if
|
|
/// at least one operand is an Instruction. In a Comparator Instruction
|
|
/// a op b, there will be 4 sigma functions a_t, a_f, b_t and b_f. Where
|
|
/// t and f represent sigma for operands in true and false branches. The
|
|
/// following constraints can be obtained. a_t <= a, a_f <= a, b_t <= b and
|
|
/// b_f <= b. There are two more constraints that depend on the operator.
|
|
/// For the operator <= : a_t <= b_t and b_f <= a_f-1
|
|
/// For the operator < : a_t <= b_t-1 and b_f <= a_f
|
|
/// For the operator >= : b_t <= a_t and a_f <= b_f-1
|
|
/// For the operator > : b_t <= a_t-1 and a_f <= b_f
|
|
void ABCD::createConstraintCmpInst(ICmpInst *ICI, TerminatorInst *TI) {
|
|
Value *V_op1 = ICI->getOperand(0);
|
|
Value *V_op2 = ICI->getOperand(1);
|
|
|
|
if (!V_op1->getType()->isIntegerTy())
|
|
return;
|
|
|
|
Instruction *I_op1 = dyn_cast<Instruction>(V_op1);
|
|
Instruction *I_op2 = dyn_cast<Instruction>(V_op2);
|
|
|
|
// Test if at least one operand is an Instruction
|
|
if (!I_op1 && !I_op2)
|
|
return;
|
|
|
|
BasicBlock *BB_succ_t = TI->getSuccessor(0);
|
|
BasicBlock *BB_succ_f = TI->getSuccessor(1);
|
|
|
|
PHINode *SIG_op1_t = NULL, *SIG_op1_f = NULL,
|
|
*SIG_op2_t = NULL, *SIG_op2_f = NULL;
|
|
|
|
createConstraintSigInst(I_op1, BB_succ_t, BB_succ_f, &SIG_op1_t, &SIG_op1_f);
|
|
createConstraintSigInst(I_op2, BB_succ_t, BB_succ_f, &SIG_op2_t, &SIG_op2_f);
|
|
|
|
int32_t width = cast<IntegerType>(V_op1->getType())->getBitWidth();
|
|
APInt MinusOne = APInt::getAllOnesValue(width);
|
|
APInt Zero = APInt::getNullValue(width);
|
|
|
|
CmpInst::Predicate Pred = ICI->getPredicate();
|
|
ConstantInt *CI1 = dyn_cast<ConstantInt>(V_op1);
|
|
ConstantInt *CI2 = dyn_cast<ConstantInt>(V_op2);
|
|
switch (Pred) {
|
|
case CmpInst::ICMP_SGT: // signed greater than
|
|
createConstraintSigSig(SIG_op2_t, SIG_op1_t, CI2, CI1, MinusOne);
|
|
createConstraintSigSig(SIG_op1_f, SIG_op2_f, CI1, CI2, Zero);
|
|
break;
|
|
|
|
case CmpInst::ICMP_SGE: // signed greater or equal
|
|
createConstraintSigSig(SIG_op2_t, SIG_op1_t, CI2, CI1, Zero);
|
|
createConstraintSigSig(SIG_op1_f, SIG_op2_f, CI1, CI2, MinusOne);
|
|
break;
|
|
|
|
case CmpInst::ICMP_SLT: // signed less than
|
|
createConstraintSigSig(SIG_op1_t, SIG_op2_t, CI1, CI2, MinusOne);
|
|
createConstraintSigSig(SIG_op2_f, SIG_op1_f, CI2, CI1, Zero);
|
|
break;
|
|
|
|
case CmpInst::ICMP_SLE: // signed less or equal
|
|
createConstraintSigSig(SIG_op1_t, SIG_op2_t, CI1, CI2, Zero);
|
|
createConstraintSigSig(SIG_op2_f, SIG_op1_f, CI2, CI1, MinusOne);
|
|
break;
|
|
|
|
default:
|
|
break;
|
|
}
|
|
|
|
if (I_op1)
|
|
createConstraintInstruction(I_op1);
|
|
if (I_op2)
|
|
createConstraintInstruction(I_op2);
|
|
}
|
|
|
|
/// Creates constraints for PHI nodes.
|
|
/// In a PHI node a = phi(b,c) we can create the constraint
|
|
/// a<= max(b,c). With this constraint there will be the edges,
|
|
/// b->a and c->a with weight 0 in the lower bound graph, and the edges
|
|
/// a->b and a->c with weight 0 in the upper bound graph.
|
|
void ABCD::createConstraintPHINode(PHINode *PN) {
|
|
// FIXME: We really want to disallow sigma nodes, but I don't know the best
|
|
// way to detect the other than this.
|
|
if (PN->getNumOperands() == 2) return;
|
|
|
|
int32_t width = cast<IntegerType>(PN->getType())->getBitWidth();
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
Value *V = PN->getIncomingValue(i);
|
|
if (Instruction *I = dyn_cast<Instruction>(V)) {
|
|
createConstraintInstruction(I);
|
|
}
|
|
inequality_graph.addEdge(V, PN, APInt(width, 0), true);
|
|
inequality_graph.addEdge(V, PN, APInt(width, 0), false);
|
|
}
|
|
}
|
|
|
|
/// This method creates a constraint between a Sigma and an Instruction.
|
|
/// These constraints are created as soon as we find a comparator that uses a
|
|
/// SSI variable.
|
|
void ABCD::createConstraintSigInst(Instruction *I_op, BasicBlock *BB_succ_t,
|
|
BasicBlock *BB_succ_f, PHINode **SIG_op_t,
|
|
PHINode **SIG_op_f) {
|
|
*SIG_op_t = findSigma(BB_succ_t, I_op);
|
|
*SIG_op_f = findSigma(BB_succ_f, I_op);
|
|
|
|
if (*SIG_op_t) {
|
|
int32_t width = cast<IntegerType>((*SIG_op_t)->getType())->getBitWidth();
|
|
inequality_graph.addEdge(I_op, *SIG_op_t, APInt(width, 0), true);
|
|
inequality_graph.addEdge(*SIG_op_t, I_op, APInt(width, 0), false);
|
|
}
|
|
if (*SIG_op_f) {
|
|
int32_t width = cast<IntegerType>((*SIG_op_f)->getType())->getBitWidth();
|
|
inequality_graph.addEdge(I_op, *SIG_op_f, APInt(width, 0), true);
|
|
inequality_graph.addEdge(*SIG_op_f, I_op, APInt(width, 0), false);
|
|
}
|
|
}
|
|
|
|
/// If PN_op1 and PN_o2 are different from NULL, create a constraint
|
|
/// PN_op2 -> PN_op1 with value. In case any of them is NULL, replace
|
|
/// with the respective V_op#, if V_op# is a ConstantInt.
|
|
void ABCD::createConstraintSigSig(PHINode *SIG_op1, PHINode *SIG_op2,
|
|
ConstantInt *V_op1, ConstantInt *V_op2,
|
|
APInt value) {
|
|
if (SIG_op1 && SIG_op2) {
|
|
inequality_graph.addEdge(SIG_op2, SIG_op1, value, true);
|
|
inequality_graph.addEdge(SIG_op1, SIG_op2, -value, false);
|
|
} else if (SIG_op1 && V_op2) {
|
|
inequality_graph.addEdge(V_op2, SIG_op1, value, true);
|
|
inequality_graph.addEdge(SIG_op1, V_op2, -value, false);
|
|
} else if (SIG_op2 && V_op1) {
|
|
inequality_graph.addEdge(SIG_op2, V_op1, value, true);
|
|
inequality_graph.addEdge(V_op1, SIG_op2, -value, false);
|
|
}
|
|
}
|
|
|
|
/// Returns the sigma representing the Instruction I in BasicBlock BB.
|
|
/// Returns NULL in case there is no sigma for this Instruction in this
|
|
/// Basic Block. This methods assume that sigmas are the first instructions
|
|
/// in a block, and that there can be only two sigmas in a block. So it will
|
|
/// only look on the first two instructions of BasicBlock BB.
|
|
PHINode *ABCD::findSigma(BasicBlock *BB, Instruction *I) {
|
|
// BB has more than one predecessor, BB cannot have sigmas.
|
|
if (I == NULL || BB->getSinglePredecessor() == NULL)
|
|
return NULL;
|
|
|
|
BasicBlock::iterator begin = BB->begin();
|
|
BasicBlock::iterator end = BB->end();
|
|
|
|
for (unsigned i = 0; i < 2 && begin != end; ++i, ++begin) {
|
|
Instruction *I_succ = begin;
|
|
if (PHINode *PN = dyn_cast<PHINode>(I_succ))
|
|
if (PN->getIncomingValue(0) == I)
|
|
return PN;
|
|
}
|
|
|
|
return NULL;
|
|
}
|
|
|
|
/// Original ABCD algorithm to prove redundant checks.
|
|
/// This implementation works on any kind of inequality branch.
|
|
bool ABCD::demandProve(Value *a, Value *b, int c, bool upper_bound) {
|
|
int32_t width = cast<IntegerType>(a->getType())->getBitWidth();
|
|
Bound *bound = new Bound(APInt(width, c), upper_bound);
|
|
|
|
mem_result.clear();
|
|
active.clear();
|
|
|
|
ProveResult res = prove(a, b, bound, 0);
|
|
return res != False;
|
|
}
|
|
|
|
/// Prove that distance between b and a is <= bound
|
|
ABCD::ProveResult ABCD::prove(Value *a, Value *b, Bound *bound,
|
|
unsigned level) {
|
|
// if (C[b-a<=e] == True for some e <= bound
|
|
// Same or stronger difference was already proven
|
|
if (mem_result.hasTrue(b, bound))
|
|
return True;
|
|
|
|
// if (C[b-a<=e] == False for some e >= bound
|
|
// Same or weaker difference was already disproved
|
|
if (mem_result.hasFalse(b, bound))
|
|
return False;
|
|
|
|
// if (C[b-a<=e] == Reduced for some e <= bound
|
|
// b is on a cycle that was reduced for same or stronger difference
|
|
if (mem_result.hasReduced(b, bound))
|
|
return Reduced;
|
|
|
|
// traversal reached the source vertex
|
|
if (a == b && Bound::geq(bound, APInt(bound->getBitWidth(), 0, true)))
|
|
return True;
|
|
|
|
// if b has no predecessor then fail
|
|
if (!inequality_graph.hasEdge(b, bound->isUpperBound()))
|
|
return False;
|
|
|
|
// a cycle was encountered
|
|
if (active.count(b)) {
|
|
if (Bound::leq(active.lookup(b), bound))
|
|
return Reduced; // a "harmless" cycle
|
|
|
|
return False; // an amplifying cycle
|
|
}
|
|
|
|
active[b] = bound;
|
|
PHINode *PN = dyn_cast<PHINode>(b);
|
|
|
|
// Test if a Value is a Phi. If it is a PHINode with more than 1 incoming
|
|
// value, then it is a phi, if it has 1 incoming value it is a sigma.
|
|
if (PN && PN->getNumIncomingValues() > 1)
|
|
updateMemDistance(a, b, bound, level, min);
|
|
else
|
|
updateMemDistance(a, b, bound, level, max);
|
|
|
|
active.erase(b);
|
|
|
|
ABCD::ProveResult res = mem_result.getBoundResult(b, bound);
|
|
return res;
|
|
}
|
|
|
|
/// Updates the distance value for a and b
|
|
void ABCD::updateMemDistance(Value *a, Value *b, Bound *bound, unsigned level,
|
|
meet_function meet) {
|
|
ABCD::ProveResult res = (meet == max) ? False : True;
|
|
|
|
SmallPtrSet<Edge *, 16> Edges = inequality_graph.getEdges(b);
|
|
SmallPtrSet<Edge *, 16>::iterator begin = Edges.begin(), end = Edges.end();
|
|
|
|
for (; begin != end ; ++begin) {
|
|
if (((res >= Reduced) && (meet == max)) ||
|
|
((res == False) && (meet == min))) {
|
|
break;
|
|
}
|
|
Edge *in = *begin;
|
|
if (in->isUpperBound() == bound->isUpperBound()) {
|
|
Value *succ = in->getVertex();
|
|
res = meet(res, prove(a, succ, new Bound(bound, in->getValue()),
|
|
level+1));
|
|
}
|
|
}
|
|
|
|
mem_result.updateBound(b, bound, res);
|
|
}
|
|
|
|
/// Return the stored result for this bound
|
|
ABCD::ProveResult ABCD::MemoizedResultChart::getResult(const Bound *bound)const{
|
|
if (max_false && Bound::leq(bound, max_false))
|
|
return False;
|
|
if (min_true && Bound::leq(min_true, bound))
|
|
return True;
|
|
if (min_reduced && Bound::leq(min_reduced, bound))
|
|
return Reduced;
|
|
return False;
|
|
}
|
|
|
|
/// Stores a false found
|
|
void ABCD::MemoizedResultChart::addFalse(Bound *bound) {
|
|
if (!max_false || Bound::leq(max_false, bound))
|
|
max_false = bound;
|
|
|
|
if (Bound::eq(max_false, min_reduced))
|
|
min_reduced = Bound::createIncrement(min_reduced);
|
|
if (Bound::eq(max_false, min_true))
|
|
min_true = Bound::createIncrement(min_true);
|
|
if (Bound::eq(min_reduced, min_true))
|
|
min_reduced = NULL;
|
|
clearRedundantReduced();
|
|
}
|
|
|
|
/// Stores a true found
|
|
void ABCD::MemoizedResultChart::addTrue(Bound *bound) {
|
|
if (!min_true || Bound::leq(bound, min_true))
|
|
min_true = bound;
|
|
|
|
if (Bound::eq(min_true, min_reduced))
|
|
min_reduced = Bound::createDecrement(min_reduced);
|
|
if (Bound::eq(min_true, max_false))
|
|
max_false = Bound::createDecrement(max_false);
|
|
if (Bound::eq(max_false, min_reduced))
|
|
min_reduced = NULL;
|
|
clearRedundantReduced();
|
|
}
|
|
|
|
/// Stores a Reduced found
|
|
void ABCD::MemoizedResultChart::addReduced(Bound *bound) {
|
|
if (!min_reduced || Bound::leq(bound, min_reduced))
|
|
min_reduced = bound;
|
|
|
|
if (Bound::eq(min_reduced, min_true))
|
|
min_true = Bound::createIncrement(min_true);
|
|
if (Bound::eq(min_reduced, max_false))
|
|
max_false = Bound::createDecrement(max_false);
|
|
}
|
|
|
|
/// Clears redundant reduced
|
|
/// If a min_true is smaller than a min_reduced then the min_reduced
|
|
/// is unnecessary and then removed. It also works for min_reduced
|
|
/// begin smaller than max_false.
|
|
void ABCD::MemoizedResultChart::clearRedundantReduced() {
|
|
if (min_true && min_reduced && Bound::lt(min_true, min_reduced))
|
|
min_reduced = NULL;
|
|
if (max_false && min_reduced && Bound::lt(min_reduced, max_false))
|
|
min_reduced = NULL;
|
|
}
|
|
|
|
/// Stores the bound found
|
|
void ABCD::MemoizedResult::updateBound(Value *b, Bound *bound,
|
|
const ProveResult res) {
|
|
if (res == False) {
|
|
map[b].addFalse(bound);
|
|
} else if (res == True) {
|
|
map[b].addTrue(bound);
|
|
} else {
|
|
map[b].addReduced(bound);
|
|
}
|
|
}
|
|
|
|
/// Adds an edge from V_from to V_to with weight value
|
|
void ABCD::InequalityGraph::addEdge(Value *V_to, Value *V_from,
|
|
APInt value, bool upper) {
|
|
assert(V_from->getType() == V_to->getType());
|
|
assert(cast<IntegerType>(V_from->getType())->getBitWidth() ==
|
|
value.getBitWidth());
|
|
|
|
DenseMap<Value *, SmallPtrSet<Edge *, 16> >::iterator from;
|
|
from = addNode(V_from);
|
|
from->second.insert(new Edge(V_to, value, upper));
|
|
}
|
|
|
|
/// Test if there is any edge from V in the upper direction
|
|
bool ABCD::InequalityGraph::hasEdge(Value *V, bool upper) const {
|
|
SmallPtrSet<Edge *, 16> it = graph.lookup(V);
|
|
|
|
SmallPtrSet<Edge *, 16>::iterator begin = it.begin();
|
|
SmallPtrSet<Edge *, 16>::iterator end = it.end();
|
|
for (; begin != end; ++begin) {
|
|
if ((*begin)->isUpperBound() == upper) {
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// Prints the header of the dot file
|
|
void ABCD::InequalityGraph::printHeader(raw_ostream &OS, Function &F) const {
|
|
OS << "digraph dotgraph {\n";
|
|
OS << "label=\"Inequality Graph for \'";
|
|
OS << F.getNameStr() << "\' function\";\n";
|
|
OS << "node [shape=record,fontname=\"Times-Roman\",fontsize=14];\n";
|
|
}
|
|
|
|
/// Prints the body of the dot file
|
|
void ABCD::InequalityGraph::printBody(raw_ostream &OS) const {
|
|
DenseMap<Value *, SmallPtrSet<Edge *, 16> >::const_iterator begin =
|
|
graph.begin(), end = graph.end();
|
|
|
|
for (; begin != end ; ++begin) {
|
|
SmallPtrSet<Edge *, 16>::iterator begin_par =
|
|
begin->second.begin(), end_par = begin->second.end();
|
|
Value *source = begin->first;
|
|
|
|
printVertex(OS, source);
|
|
|
|
for (; begin_par != end_par ; ++begin_par) {
|
|
Edge *edge = *begin_par;
|
|
printEdge(OS, source, edge);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Prints vertex source to the dot file
|
|
///
|
|
void ABCD::InequalityGraph::printVertex(raw_ostream &OS, Value *source) const {
|
|
OS << "\"";
|
|
printName(OS, source);
|
|
OS << "\"";
|
|
OS << " [label=\"{";
|
|
printName(OS, source);
|
|
OS << "}\"];\n";
|
|
}
|
|
|
|
/// Prints the edge to the dot file
|
|
void ABCD::InequalityGraph::printEdge(raw_ostream &OS, Value *source,
|
|
Edge *edge) const {
|
|
Value *dest = edge->getVertex();
|
|
APInt value = edge->getValue();
|
|
bool upper = edge->isUpperBound();
|
|
|
|
OS << "\"";
|
|
printName(OS, source);
|
|
OS << "\"";
|
|
OS << " -> ";
|
|
OS << "\"";
|
|
printName(OS, dest);
|
|
OS << "\"";
|
|
OS << " [label=\"" << value << "\"";
|
|
if (upper) {
|
|
OS << "color=\"blue\"";
|
|
} else {
|
|
OS << "color=\"red\"";
|
|
}
|
|
OS << "];\n";
|
|
}
|
|
|
|
void ABCD::InequalityGraph::printName(raw_ostream &OS, Value *info) const {
|
|
if (ConstantInt *CI = dyn_cast<ConstantInt>(info)) {
|
|
OS << *CI;
|
|
} else {
|
|
if (!info->hasName()) {
|
|
info->setName("V");
|
|
}
|
|
OS << info->getNameStr();
|
|
}
|
|
}
|
|
|
|
/// createABCDPass - The public interface to this file...
|
|
FunctionPass *llvm::createABCDPass() {
|
|
return new ABCD();
|
|
}
|