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84354d97d5
Identified by Pedro Giffuni in PR27636. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287489 91177308-0d34-0410-b5e6-96231b3b80d8
209 lines
7.8 KiB
C++
209 lines
7.8 KiB
C++
//===- ListReducer.h - Trim down list while retaining property --*- 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 class is to be used as a base class for operations that want to zero in
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// on a subset of the input which still causes the bug we are tracking.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TOOLS_BUGPOINT_LISTREDUCER_H
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#define LLVM_TOOLS_BUGPOINT_LISTREDUCER_H
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#include "llvm/Support/Error.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <cstdlib>
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#include <vector>
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namespace llvm {
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extern bool BugpointIsInterrupted;
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template <typename ElTy> struct ListReducer {
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enum TestResult {
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NoFailure, // No failure of the predicate was detected
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KeepSuffix, // The suffix alone satisfies the predicate
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KeepPrefix // The prefix alone satisfies the predicate
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};
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virtual ~ListReducer() {}
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/// This virtual function should be overriden by subclasses to implement the
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/// test desired. The testcase is only required to test to see if the Kept
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/// list still satisfies the property, but if it is going to check the prefix
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/// anyway, it can.
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virtual Expected<TestResult> doTest(std::vector<ElTy> &Prefix,
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std::vector<ElTy> &Kept) = 0;
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/// This function attempts to reduce the length of the specified list while
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/// still maintaining the "test" property. This is the core of the "work"
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/// that bugpoint does.
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Expected<bool> reduceList(std::vector<ElTy> &TheList) {
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std::vector<ElTy> empty;
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std::srand(0x6e5ea738); // Seed the random number generator
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Expected<TestResult> Result = doTest(TheList, empty);
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if (Error E = Result.takeError())
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return std::move(E);
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switch (*Result) {
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case KeepPrefix:
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if (TheList.size() == 1) // we are done, it's the base case and it fails
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return true;
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else
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break; // there's definitely an error, but we need to narrow it down
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case KeepSuffix:
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// cannot be reached!
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llvm_unreachable("bugpoint ListReducer internal error: "
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"selected empty set.");
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case NoFailure:
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return false; // there is no failure with the full set of passes/funcs!
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}
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// Maximal number of allowed splitting iterations,
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// before the elements are randomly shuffled.
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const unsigned MaxIterationsWithoutProgress = 3;
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// Maximal number of allowed single-element trim iterations. We add a
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// threshold here as single-element reductions may otherwise take a
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// very long time to complete.
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const unsigned MaxTrimIterationsWithoutBackJump = 3;
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bool ShufflingEnabled = true;
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Backjump:
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unsigned MidTop = TheList.size();
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unsigned MaxIterations = MaxIterationsWithoutProgress;
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unsigned NumOfIterationsWithoutProgress = 0;
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while (MidTop > 1) { // Binary split reduction loop
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// Halt if the user presses ctrl-c.
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if (BugpointIsInterrupted) {
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errs() << "\n\n*** Reduction Interrupted, cleaning up...\n\n";
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return true;
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}
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// If the loop doesn't make satisfying progress, try shuffling.
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// The purpose of shuffling is to avoid the heavy tails of the
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// distribution (improving the speed of convergence).
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if (ShufflingEnabled && NumOfIterationsWithoutProgress > MaxIterations) {
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std::vector<ElTy> ShuffledList(TheList);
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std::random_shuffle(ShuffledList.begin(), ShuffledList.end());
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errs() << "\n\n*** Testing shuffled set...\n\n";
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// Check that random shuffle doesn't lose the bug
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Expected<TestResult> Result = doTest(ShuffledList, empty);
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// TODO: Previously, this error was ignored and we treated it as if
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// shuffling hid the bug. This should really either be consumeError if
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// that behaviour was sensible, or we should propagate the error.
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assert(!Result.takeError() && "Shuffling caused internal error?");
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if (*Result == KeepPrefix) {
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// If the bug is still here, use the shuffled list.
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TheList.swap(ShuffledList);
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MidTop = TheList.size();
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// Must increase the shuffling treshold to avoid the small
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// probability of infinite looping without making progress.
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MaxIterations += 2;
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errs() << "\n\n*** Shuffling does not hide the bug...\n\n";
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} else {
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ShufflingEnabled = false; // Disable shuffling further on
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errs() << "\n\n*** Shuffling hides the bug...\n\n";
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}
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NumOfIterationsWithoutProgress = 0;
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}
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unsigned Mid = MidTop / 2;
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std::vector<ElTy> Prefix(TheList.begin(), TheList.begin() + Mid);
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std::vector<ElTy> Suffix(TheList.begin() + Mid, TheList.end());
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Expected<TestResult> Result = doTest(Prefix, Suffix);
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if (Error E = Result.takeError())
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return std::move(E);
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switch (*Result) {
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case KeepSuffix:
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// The property still holds. We can just drop the prefix elements, and
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// shorten the list to the "kept" elements.
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TheList.swap(Suffix);
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MidTop = TheList.size();
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// Reset progress treshold and progress counter
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MaxIterations = MaxIterationsWithoutProgress;
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NumOfIterationsWithoutProgress = 0;
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break;
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case KeepPrefix:
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// The predicate still holds, shorten the list to the prefix elements.
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TheList.swap(Prefix);
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MidTop = TheList.size();
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// Reset progress treshold and progress counter
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MaxIterations = MaxIterationsWithoutProgress;
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NumOfIterationsWithoutProgress = 0;
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break;
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case NoFailure:
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// Otherwise the property doesn't hold. Some of the elements we removed
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// must be necessary to maintain the property.
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MidTop = Mid;
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NumOfIterationsWithoutProgress++;
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break;
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}
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}
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// Probability of backjumping from the trimming loop back to the binary
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// split reduction loop.
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const int BackjumpProbability = 10;
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// Okay, we trimmed as much off the top and the bottom of the list as we
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// could. If there is more than two elements in the list, try deleting
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// interior elements and testing that.
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//
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if (TheList.size() > 2) {
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bool Changed = true;
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std::vector<ElTy> EmptyList;
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unsigned TrimIterations = 0;
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while (Changed) { // Trimming loop.
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Changed = false;
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// If the binary split reduction loop made an unfortunate sequence of
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// splits, the trimming loop might be left off with a huge number of
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// remaining elements (large search space). Backjumping out of that
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// search space and attempting a different split can significantly
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// improve the convergence speed.
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if (std::rand() % 100 < BackjumpProbability)
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goto Backjump;
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for (unsigned i = 1; i < TheList.size() - 1; ++i) {
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// Check interior elts
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if (BugpointIsInterrupted) {
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errs() << "\n\n*** Reduction Interrupted, cleaning up...\n\n";
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return true;
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}
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std::vector<ElTy> TestList(TheList);
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TestList.erase(TestList.begin() + i);
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Expected<TestResult> Result = doTest(EmptyList, TestList);
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if (Error E = Result.takeError())
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return std::move(E);
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if (*Result == KeepSuffix) {
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// We can trim down the list!
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TheList.swap(TestList);
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--i; // Don't skip an element of the list
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Changed = true;
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}
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}
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if (TrimIterations >= MaxTrimIterationsWithoutBackJump)
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break;
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TrimIterations++;
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}
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}
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return true; // there are some failure and we've narrowed them down
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}
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};
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} // End llvm namespace
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#endif
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