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//-----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation. All Rights Reserved.
//
//-----------------------------------------------------------------------------
using Microsoft.Contracts;
using System.Collections.Generic;
using Cci = System.Compiler;
using Bpl = Microsoft.Boogie;
namespace Microsoft.Boogie
{
public class LoopUnroll {
public static List<Block!>! UnrollLoops(Block! start, int unrollMaxDepth)
requires 0 <= unrollMaxDepth;
{
Dictionary<Block,GraphNode!> gd = new Dictionary<Block,GraphNode!>();
Cci.HashSet/*Block*/! beingVisited = new Cci.HashSet/*Block*/();
GraphNode gStart = GraphNode.ComputeGraphInfo(null, start, gd, beingVisited);
LoopUnroll lu = new LoopUnroll(gd, unrollMaxDepth, null);
lu.Visit(gStart);
lu.newBlockSeqGlobal.Reverse();
return lu.newBlockSeqGlobal;
}
class GraphNode {
public readonly Block! Block;
public readonly CmdSeq! Body;
bool isCutPoint; // is set during ComputeGraphInfo
public bool IsCutPoint { get { return isCutPoint; } }
[Rep] public readonly List<GraphNode!>! ForwardEdges = new List<GraphNode!>();
[Rep] public readonly List<GraphNode!>! BackEdges = new List<GraphNode!>();
invariant isCutPoint <==> BackEdges.Count != 0;
GraphNode(Block! b, CmdSeq! body) {
this.Block = b;
this.Body = body;
}
static CmdSeq! GetOptimizedBody(CmdSeq! cmds) {
int n = 0;
foreach (Cmd c in cmds) {
n++;
PredicateCmd pc = c as PredicateCmd;
if (pc != null && pc.Expr is LiteralExpr && ((LiteralExpr)pc.Expr).IsFalse) {
// return a sequence consisting of the commands seen so far
Cmd[] s = new Cmd[n];
for (int i = 0; i < n; i++) {
s[i] = cmds[i];
}
return new CmdSeq(s);
}
}
return cmds;
}
public static GraphNode! ComputeGraphInfo(GraphNode from, Block! b, Dictionary<Block,GraphNode!>! gd, Cci.HashSet/*Block*/! beingVisited) {
GraphNode g;
if (gd.TryGetValue(b, out g)) {
assume from != null;
assert g != null;
if (beingVisited.Contains(b)) {
// it's a cut point
g.isCutPoint = true;
from.BackEdges.Add(g);
} else {
from.ForwardEdges.Add(g);
}
} else {
CmdSeq body = GetOptimizedBody(b.Cmds);
g = new GraphNode(b, body);
gd.Add(b, g);
if (from != null) {
from.ForwardEdges.Add(g);
}
if (body != b.Cmds) {
// the body was optimized -- there is no way through this block
} else {
beingVisited.Add(b);
GotoCmd gcmd = b.TransferCmd as GotoCmd;
if (gcmd != null) {
assume gcmd.labelTargets != null;
foreach (Block! succ in gcmd.labelTargets) {
ComputeGraphInfo(g, succ, gd, beingVisited);
}
}
beingVisited.Remove(b);
}
}
return g;
}
}
List<Block!>! newBlockSeqGlobal;
readonly int c;
readonly LoopUnroll next;
Dictionary<Block,int>! visitsRemaining = new Dictionary</*cut-point-*/Block,int>();
Dictionary<Block,Block!>! newBlocks = new Dictionary<Block,Block!>();
private LoopUnroll(Dictionary<Block,GraphNode!>! gd, int unrollMaxDepth, List<Block!> newBlockSeqGlobal)
requires 0 <= unrollMaxDepth;
{
if (newBlockSeqGlobal == null) {
newBlockSeqGlobal = new List<Block!>();
}
this.newBlockSeqGlobal = newBlockSeqGlobal;
this.c = unrollMaxDepth;
if (unrollMaxDepth != 0) {
next = new LoopUnroll(gd, unrollMaxDepth - 1, newBlockSeqGlobal);
}
}
Block! Visit(GraphNode! node) {
Block orig = node.Block;
Block nw;
if (newBlocks.TryGetValue(orig, out nw)) {
assert nw != null;
} else {
CmdSeq body;
TransferCmd tcmd;
assert orig.TransferCmd != null;
if (next == null && node.IsCutPoint) {
// as the body, use the assert/assume commands that make up the loop invariant
body = new CmdSeq();
foreach (Cmd! c in node.Body) {
if (c is PredicateCmd || c is CommentCmd) {
body.Add(c);
} else {
break;
}
}
body.Add(new AssumeCmd(orig.tok, Bpl.Expr.False));
tcmd = new ReturnCmd(orig.TransferCmd.tok);
} else {
body = node.Body;
BlockSeq newSuccs = new BlockSeq();
foreach (GraphNode succ in node.ForwardEdges) {
Block s = Visit(succ);
newSuccs.Add(s);
}
assert next == null ==> node.BackEdges.Count == 0; // follows from if-else test above and the GraphNode invariant
foreach (GraphNode succ in node.BackEdges) {
assert next != null; // since if we get here, node.BackEdges.Count != 0
Block s = next.Visit(succ);
newSuccs.Add(s);
}
if (newSuccs.Length == 0) {
tcmd = new ReturnCmd(orig.TransferCmd.tok);
} else {
tcmd = new GotoCmd(orig.TransferCmd.tok, newSuccs);
}
}
nw = new Block(orig.tok, orig.Label + "#" + this.c, body, tcmd);
newBlocks.Add(orig, nw);
newBlockSeqGlobal.Add(nw);
}
return nw;
}
}
}
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