No cache (#964)

### Changes
- Enable not using a verification result cache, using the new class
`EmptyVerificationResultCache`

### Testing
- Manually tried out using EmptyVerificationResultCache in Dafny, which
reduces memory pressure

Source/Directory.Build.props

@@ -2,7 +2,7 @@
 
   <!-- Target framework and package configuration -->
   <PropertyGroup>
-    <Version>3.3.1</Version>
+    <Version>3.3.2</Version>
     <TargetFramework>net6.0</TargetFramework>
     <GeneratePackageOnBuild>false</GeneratePackageOnBuild>
     <Authors>Boogie</Authors>

Source/ExecutionEngine/Caching/CachedVerificationResultInjector.cs

@@ -0,0 +1,313 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Contracts;
+using System.Linq;
+using VC;
+
+namespace Microsoft.Boogie;
+
+sealed class CachedVerificationResultInjector : StandardVisitor
+{
+  private ExecutionEngineOptions options;
+  readonly Program Program;
+
+  // TODO(wuestholz): We should probably increase the threshold to something like 2 seconds.
+  static readonly double TimeThreshold = -1.0d;
+  Program programInCachedSnapshot;
+  Implementation currentImplementation;
+  int assumptionVariableCount;
+  int temporaryVariableCount;
+
+  public static readonly CachedVerificationResultInjectorStatistics Statistics =
+    new CachedVerificationResultInjectorStatistics();
+
+  int FreshAssumptionVariableName
+  {
+    get { return assumptionVariableCount++; }
+  }
+
+  int FreshTemporaryVariableName
+  {
+    get { return temporaryVariableCount++; }
+  }
+
+  CachedVerificationResultInjector(ExecutionEngineOptions options, Program program)
+  {
+    Program = program;
+    this.options = options;
+  }
+
+  public Implementation Inject(Implementation implementation, Program programInCachedSnapshot)
+  {
+    Contract.Requires(implementation != null && programInCachedSnapshot != null);
+
+    this.programInCachedSnapshot = programInCachedSnapshot;
+    assumptionVariableCount = 0;
+    temporaryVariableCount = 0;
+    currentImplementation = implementation;
+
+    #region Introduce explict assumption about the precondition.
+
+    var oldProc = programInCachedSnapshot.FindProcedure(currentImplementation.Proc.Name);
+    if (oldProc != null
+        && oldProc.DependencyChecksum != currentImplementation.Proc.DependencyChecksum
+        && currentImplementation.ExplicitAssumptionAboutCachedPrecondition == null)
+    {
+      var axioms = new List<Axiom>();
+      var after = new List<Cmd>();
+      Expr assumedExpr = new LiteralExpr(Token.NoToken, false);
+      var canUseSpecs = DependencyCollector.CanExpressOldSpecs(oldProc, Program, true);
+      if (canUseSpecs && oldProc.SignatureEquals(options, currentImplementation.Proc))
+      {
+        var always = Substituter.SubstitutionFromDictionary(currentImplementation.GetImplFormalMap(options), true,
+          currentImplementation.Proc);
+        var forOld = Substituter.SubstitutionFromDictionary(new Dictionary<Variable, Expr>());
+        var clauses = oldProc.Requires.Select(r =>
+          Substituter.FunctionCallReresolvingApply(always, forOld, r.Condition, Program));
+        var conj = Expr.And(clauses, true);
+        assumedExpr = conj != null
+          ? FunctionExtractor.Extract(conj, Program, axioms)
+          : new LiteralExpr(Token.NoToken, true);
+      }
+
+      if (assumedExpr != null)
+      {
+        var lv = new LocalVariable(Token.NoToken,
+          new TypedIdent(Token.NoToken, string.Format("a##cached##{0}", FreshAssumptionVariableName), Type.Bool),
+          new QKeyValue(Token.NoToken, "assumption", new List<object>(), null));
+        currentImplementation.InjectAssumptionVariable(lv, !canUseSpecs);
+        var lhs = new SimpleAssignLhs(Token.NoToken, new IdentifierExpr(Token.NoToken, lv));
+        var rhs = LiteralExpr.And(new IdentifierExpr(Token.NoToken, lv), assumedExpr);
+        var assumed = new AssignCmd(currentImplementation.tok, new List<AssignLhs> {lhs}, new List<Expr> {rhs});
+        assumed.IrrelevantForChecksumComputation = true;
+        currentImplementation.ExplicitAssumptionAboutCachedPrecondition = assumed;
+        after.Add(assumed);
+      }
+
+      if (options.TraceCachingForTesting || options.TraceCachingForBenchmarking) {
+        using var tokTxtWr = new TokenTextWriter("<console>", options.OutputWriter, false, false, options);
+        var loc = currentImplementation.tok != null && currentImplementation.tok != Token.NoToken
+          ? string.Format("{0}({1},{2})", currentImplementation.tok.filename, currentImplementation.tok.line,
+            currentImplementation.tok.col)
+          : "<unknown location>";
+        options.OutputWriter.WriteLine("Processing implementation {0} (at {1}):", currentImplementation.VerboseName, loc);
+        foreach (var a in axioms)
+        {
+          options.OutputWriter.Write("  >>> added axiom: ");
+          a.Expr.Emit(tokTxtWr);
+          options.OutputWriter.WriteLine();
+        }
+
+        foreach (var b in after)
+        {
+          options.OutputWriter.Write("  >>> added after assuming the current precondition: ");
+          b.Emit(tokTxtWr, 0);
+        }
+      }
+    }
+
+    #endregion
+
+    var result = VisitImplementation(currentImplementation);
+    currentImplementation = null;
+    this.programInCachedSnapshot = null;
+    return result;
+  }
+
+  public static void Inject(ExecutionEngine engine, Program program, 
+    IReadOnlyList<Implementation> implementations, string requestId,
+    string programId, out long[] cachingActionCounts)
+  {
+    var eai = new CachedVerificationResultInjector(engine.Options, program);
+
+    cachingActionCounts = new long[Enum.GetNames(typeof(VC.ConditionGeneration.CachingAction)).Length];
+    var run = new CachedVerificationResultInjectorRun
+    {
+      Start = DateTime.UtcNow, ImplementationCount = implementations.Count(),
+      CachingActionCounts = cachingActionCounts
+    };
+    foreach (var impl in implementations)
+    {
+      var vr = engine.Cache.Lookup(impl, engine.Options.RunDiagnosticsOnTimeout, out var priority);
+      if (vr != null && vr.ProgramId == programId)
+      {
+        if (priority == Priority.LOW)
+        {
+          run.LowPriorityImplementationCount++;
+        }
+        else if (priority == Priority.MEDIUM)
+        {
+          run.MediumPriorityImplementationCount++;
+        }
+        else if (priority == Priority.HIGH)
+        {
+          run.HighPriorityImplementationCount++;
+        }
+        else if (priority == Priority.SKIP)
+        {
+          run.SkippedImplementationCount++;
+        }
+
+        if (priority == Priority.LOW || priority == Priority.MEDIUM || engine.Options.VerifySnapshots >= 3)
+        {
+          if (TimeThreshold < vr.End.Subtract(vr.Start).TotalMilliseconds)
+          {
+            eai.SetErrorAndAssertionChecksumsInCachedSnapshot(impl, vr);
+            if (vr.ProgramId != null)
+            {
+              var p = engine.Cache.CachedProgram(vr.ProgramId);
+              if (p != null)
+              {
+                eai.Inject(impl, p);
+                run.TransformedImplementationCount++;
+              }
+            }
+          }
+        }
+      }
+    }
+
+    run.End = DateTime.UtcNow;
+    Statistics.AddRun(requestId, run);
+  }
+
+  private void SetErrorAndAssertionChecksumsInCachedSnapshot(Implementation implementation,
+    ImplementationRunResult result)
+  {
+    if (result.VcOutcome == VcOutcome.Errors && result.Errors != null &&
+        result.Errors.Count < options.ErrorLimit)
+    {
+      implementation.SetErrorChecksumToCachedError(result.Errors.Select(cex =>
+        new Tuple<byte[], byte[], object>(cex.Checksum, cex.SugaredCmdChecksum, cex)));
+      implementation.AssertionChecksumsInCachedSnapshot = result.AssertionChecksums;
+    }
+    else if (result.VcOutcome == VcOutcome.Correct)
+    {
+      implementation.SetErrorChecksumToCachedError(new List<Tuple<byte[], byte[], object>>());
+      implementation.AssertionChecksumsInCachedSnapshot = result.AssertionChecksums;
+    }
+  }
+
+  public override Cmd VisitCallCmd(CallCmd node)
+  {
+    var result = base.VisitCallCmd(node);
+
+    var oldProc = programInCachedSnapshot.FindProcedure(node.Proc.Name);
+    if (oldProc != null
+        && oldProc.DependencyChecksum != node.Proc.DependencyChecksum
+        && node.AssignedAssumptionVariable == null)
+    {
+      var before = new List<Cmd>();
+      var beforePreconditionCheck = new List<Cmd>();
+      var after = new List<Cmd>();
+      var axioms = new List<Axiom>();
+      Expr assumedExpr = new LiteralExpr(Token.NoToken, false);
+      // TODO(wuestholz): Try out two alternatives: only do this for low priority implementations or not at all.
+      var canUseSpecs = DependencyCollector.CanExpressOldSpecs(oldProc, Program);
+      if (canUseSpecs && oldProc.SignatureEquals(options, node.Proc))
+      {
+        var desugaring = node.GetDesugaring(options);
+        Contract.Assert(desugaring != null);
+        var precond = node.CheckedPrecondition(oldProc, Program, e => FunctionExtractor.Extract(e, Program, axioms));
+        if (precond != null)
+        {
+          var assume = new AssumeCmd(node.tok, precond,
+            new QKeyValue(Token.NoToken, "precondition_previous_snapshot", new List<object>(), null));
+          assume.IrrelevantForChecksumComputation = true;
+          beforePreconditionCheck.Add(assume);
+        }
+
+        var unmods = node.UnmodifiedBefore(oldProc);
+        var eqs = new List<Expr>();
+        foreach (var unmod in unmods)
+        {
+          var oldUnmod = new LocalVariable(Token.NoToken,
+            new TypedIdent(Token.NoToken, string.Format("{0}##old##{1}", unmod.Name, FreshTemporaryVariableName),
+              unmod.Type));
+          var lhs = new SimpleAssignLhs(Token.NoToken, new IdentifierExpr(Token.NoToken, oldUnmod));
+          var rhs = new IdentifierExpr(Token.NoToken, unmod.Decl);
+          var cmd = new AssignCmd(Token.NoToken, new List<AssignLhs> {lhs}, new List<Expr> {rhs});
+          cmd.IrrelevantForChecksumComputation = true;
+          before.Add(cmd);
+          var eq = LiteralExpr.Eq(new IdentifierExpr(Token.NoToken, oldUnmod),
+            new IdentifierExpr(Token.NoToken, unmod.Decl));
+          eq.Type = Type.Bool;
+          eq.TypeParameters = SimpleTypeParamInstantiation.EMPTY;
+          eqs.Add(eq);
+        }
+
+        var mods = node.ModifiedBefore(oldProc);
+        var oldSubst = new Dictionary<Variable, Expr>();
+        foreach (var mod in mods)
+        {
+          var oldMod = new LocalVariable(Token.NoToken,
+            new TypedIdent(Token.NoToken, string.Format("{0}##old##{1}", mod.Name, FreshTemporaryVariableName),
+              mod.Type));
+          oldSubst[mod.Decl] = new IdentifierExpr(Token.NoToken, oldMod);
+          var lhs = new SimpleAssignLhs(Token.NoToken, new IdentifierExpr(Token.NoToken, oldMod));
+          var rhs = new IdentifierExpr(Token.NoToken, mod.Decl);
+          var cmd = new AssignCmd(Token.NoToken, new List<AssignLhs> {lhs}, new List<Expr> {rhs});
+          cmd.IrrelevantForChecksumComputation = true;
+          before.Add(cmd);
+        }
+
+        assumedExpr = node.Postcondition(oldProc, eqs, oldSubst, Program,
+          e => FunctionExtractor.Extract(e, Program, axioms));
+        if (assumedExpr == null)
+        {
+          assumedExpr = new LiteralExpr(Token.NoToken, true);
+        }
+      }
+
+      if (assumedExpr != null)
+      {
+        var lv = new LocalVariable(Token.NoToken,
+          new TypedIdent(Token.NoToken, string.Format("a##cached##{0}", FreshAssumptionVariableName), Type.Bool),
+          new QKeyValue(Token.NoToken, "assumption", new List<object>(), null));
+        node.AssignedAssumptionVariable = lv;
+        currentImplementation.InjectAssumptionVariable(lv, !canUseSpecs);
+        var lhs = new SimpleAssignLhs(Token.NoToken, new IdentifierExpr(Token.NoToken, lv));
+        var rhs = LiteralExpr.And(new IdentifierExpr(Token.NoToken, lv), assumedExpr);
+        var assumed = new AssignCmd(node.tok, new List<AssignLhs> {lhs}, new List<Expr> {rhs});
+        assumed.IrrelevantForChecksumComputation = true;
+        after.Add(assumed);
+      }
+
+      node.ExtendDesugaring(options, before, beforePreconditionCheck, after);
+      if (options.TraceCachingForTesting || options.TraceCachingForBenchmarking) {
+        using var tokTxtWr = new TokenTextWriter("<console>", options.OutputWriter, false, false, options);
+        var loc = node.tok != null && node.tok != Token.NoToken
+          ? $"{node.tok.filename}({node.tok.line},{node.tok.col})"
+          : "<unknown location>";
+        options.OutputWriter.WriteLine("Processing call to procedure {0} in implementation {1} (at {2}):", node.Proc.VerboseName,
+          currentImplementation.VerboseName, loc);
+        foreach (var a in axioms)
+        {
+          options.OutputWriter.Write("  >>> added axiom: ");
+          a.Expr.Emit(tokTxtWr);
+          options.OutputWriter.WriteLine();
+        }
+
+        foreach (var b in before)
+        {
+          options.OutputWriter.Write("  >>> added before: ");
+          b.Emit(tokTxtWr, 0);
+        }
+
+        foreach (var b in beforePreconditionCheck)
+        {
+          options.OutputWriter.Write("  >>> added before precondition check: ");
+          b.Emit(tokTxtWr, 0);
+        }
+
+        foreach (var a in after)
+        {
+          options.OutputWriter.Write("  >>> added after: ");
+          a.Emit(tokTxtWr, 0);
+        }
+      }
+    }
+
+    return result;
+  }
+}

Source/ExecutionEngine/Caching/CachedVerificationResultInjectorRun.cs

@@ -0,0 +1,24 @@
+using System;
+
+namespace Microsoft.Boogie;
+
+struct CachedVerificationResultInjectorRun
+{
+  public DateTime Start { get; internal set; }
+
+  public DateTime End { get; internal set; }
+
+  public int TransformedImplementationCount { get; internal set; }
+
+  public int ImplementationCount { get; internal set; }
+
+  public int SkippedImplementationCount { get; set; }
+
+  public int LowPriorityImplementationCount { get; set; }
+
+  public int MediumPriorityImplementationCount { get; set; }
+
+  public int HighPriorityImplementationCount { get; set; }
+
+  public long[] CachingActionCounts { get; set; }
+}

Source/ExecutionEngine/Caching/CachedVerificationResultInjectorStatistics.cs

@@ -0,0 +1,35 @@
+using System.Collections.Concurrent;
+using System.IO;
+using System.Linq;
+
+namespace Microsoft.Boogie;
+
+sealed class CachedVerificationResultInjectorStatistics
+{
+  ConcurrentDictionary<string, CachedVerificationResultInjectorRun> runs =
+    new ConcurrentDictionary<string, CachedVerificationResultInjectorRun>();
+
+  public bool AddRun(string requestId, CachedVerificationResultInjectorRun run)
+  {
+    return runs.TryAdd(requestId, run);
+  }
+
+  public string Output(bool printTime = false)
+  {
+    var wr = new StringWriter();
+    if (runs.Any())
+    {
+      wr.WriteLine("Cached verification result injector statistics as CSV:");
+      wr.WriteLine("Request ID, Transformed, Low, Medium, High, Skipped{0}", printTime ? ", Time (ms)" : "");
+      foreach (var kv in runs.OrderBy(kv => ExecutionEngine.AutoRequestId(kv.Key)))
+      {
+        var t = printTime ? string.Format(", {0,8:F0}", kv.Value.End.Subtract(kv.Value.Start).TotalMilliseconds) : "";
+        wr.WriteLine("{0,-19}, {1,3}, {2,3}, {3,3}, {4,3}, {5,3}{6}", kv.Key, kv.Value.TransformedImplementationCount,
+          kv.Value.LowPriorityImplementationCount, kv.Value.MediumPriorityImplementationCount,
+          kv.Value.HighPriorityImplementationCount, kv.Value.SkippedImplementationCount, t);
+      }
+    }
+
+    return wr.ToString();
+  }
+}