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//===- ListReducer.h - Trim down list while retaining property --*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This class is to be used as a base class for operations that want to zero in
// on a subset of the input which still causes the bug we are tracking.
//
//===----------------------------------------------------------------------===//
#ifndef BUGPOINT_LIST_REDUCER_H
#define BUGPOINT_LIST_REDUCER_H
#include <vector>
#include <iostream>
#include <cstdlib>
#include <algorithm>
namespace llvm {
extern bool BugpointIsInterrupted;
template<typename ElTy>
struct ListReducer {
enum TestResult {
NoFailure, // No failure of the predicate was detected
KeepSuffix, // The suffix alone satisfies the predicate
KeepPrefix // The prefix alone satisfies the predicate
};
virtual ~ListReducer() {}
// doTest - This virtual function should be overriden by subclasses to
// implement the test desired. The testcase is only required to test to see
// if the Kept list still satisfies the property, but if it is going to check
// the prefix anyway, it can.
//
virtual TestResult doTest(std::vector<ElTy> &Prefix,
std::vector<ElTy> &Kept) = 0;
// reduceList - This function attempts to reduce the length of the specified
// list while still maintaining the "test" property. This is the core of the
// "work" that bugpoint does.
//
bool reduceList(std::vector<ElTy> &TheList) {
std::vector<ElTy> empty;
std::srand(0x6e5ea738); // Seed the random number generator
switch (doTest(TheList, empty)) {
case KeepPrefix:
if (TheList.size() == 1) // we are done, it's the base case and it fails
return true;
else
break; // there's definitely an error, but we need to narrow it down
case KeepSuffix:
// cannot be reached!
std::cerr << "bugpoint ListReducer internal error: selected empty set.\n";
abort();
case NoFailure:
return false; // there is no failure with the full set of passes/funcs!
}
// Maximal number of allowed splitting iterations,
// before the elements are randomly shuffled.
const unsigned MaxIterationsWithoutProgress = 3;
bool ShufflingEnabled = true;
Backjump:
unsigned MidTop = TheList.size();
unsigned MaxIterations = MaxIterationsWithoutProgress;
unsigned NumOfIterationsWithoutProgress = 0;
while (MidTop > 1) { // Binary split reduction loop
// Halt if the user presses ctrl-c.
if (BugpointIsInterrupted) {
std::cerr << "\n\n*** Reduction Interrupted, cleaning up...\n\n";
return true;
}
// If the loop doesn't make satisfying progress, try shuffling.
// The purpose of shuffling is to avoid the heavy tails of the
// distribution (improving the speed of convergence).
if (ShufflingEnabled &&
NumOfIterationsWithoutProgress > MaxIterations) {
std::vector<ElTy> ShuffledList(TheList);
std::random_shuffle(ShuffledList.begin(), ShuffledList.end());
std::cerr << "\n\n*** Testing shuffled set...\n\n";
// Check that random shuffle doesn't loose the bug
if (doTest(ShuffledList, empty) == KeepPrefix) {
// If the bug is still here, use the shuffled list.
TheList.swap(ShuffledList);
MidTop = TheList.size();
// Must increase the shuffling treshold to avoid the small
// probability of inifinite looping without making progress.
MaxIterations += 2;
std::cerr << "\n\n*** Shuffling does not hide the bug...\n\n";
} else {
ShufflingEnabled = false; // Disable shuffling further on
std::cerr << "\n\n*** Shuffling hides the bug...\n\n";
}
NumOfIterationsWithoutProgress = 0;
}
unsigned Mid = MidTop / 2;
std::vector<ElTy> Prefix(TheList.begin(), TheList.begin()+Mid);
std::vector<ElTy> Suffix(TheList.begin()+Mid, TheList.end());
switch (doTest(Prefix, Suffix)) {
case KeepSuffix:
// The property still holds. We can just drop the prefix elements, and
// shorten the list to the "kept" elements.
TheList.swap(Suffix);
MidTop = TheList.size();
// Reset progress treshold and progress counter
MaxIterations = MaxIterationsWithoutProgress;
NumOfIterationsWithoutProgress = 0;
break;
case KeepPrefix:
// The predicate still holds, shorten the list to the prefix elements.
TheList.swap(Prefix);
MidTop = TheList.size();
// Reset progress treshold and progress counter
MaxIterations = MaxIterationsWithoutProgress;
NumOfIterationsWithoutProgress = 0;
break;
case NoFailure:
// Otherwise the property doesn't hold. Some of the elements we removed
// must be necessary to maintain the property.
MidTop = Mid;
NumOfIterationsWithoutProgress++;
break;
}
}
// Probability of backjumping from the trimming loop back to the binary
// split reduction loop.
const int BackjumpProbability = 10;
// Okay, we trimmed as much off the top and the bottom of the list as we
// could. If there is more than two elements in the list, try deleting
// interior elements and testing that.
//
if (TheList.size() > 2) {
bool Changed = true;
std::vector<ElTy> EmptyList;
while (Changed) { // Trimming loop.
Changed = false;
// If the binary split reduction loop made an unfortunate sequence of
// splits, the trimming loop might be left off with a huge number of
// remaining elements (large search space). Backjumping out of that
// search space and attempting a different split can significantly
// improve the convergence speed.
if (std::rand() % 100 < BackjumpProbability)
goto Backjump;
for (unsigned i = 1; i < TheList.size()-1; ++i) { // Check interior elts
if (BugpointIsInterrupted) {
std::cerr << "\n\n*** Reduction Interrupted, cleaning up...\n\n";
return true;
}
std::vector<ElTy> TestList(TheList);
TestList.erase(TestList.begin()+i);
if (doTest(EmptyList, TestList) == KeepSuffix) {
// We can trim down the list!
TheList.swap(TestList);
--i; // Don't skip an element of the list
Changed = true;
}
}
// This can take a long time if left uncontrolled. For now, don't
// iterate.
break;
}
}
return true; // there are some failure and we've narrowed them down
}
};
} // End llvm namespace
#endif
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