mirror of https://github.com/icsharpcode/ILSpy.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
310 lines
14 KiB
310 lines
14 KiB
// Copyright (c) 2014 Daniel Grunwald |
|
// |
|
// Permission is hereby granted, free of charge, to any person obtaining a copy of this |
|
// software and associated documentation files (the "Software"), to deal in the Software |
|
// without restriction, including without limitation the rights to use, copy, modify, merge, |
|
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons |
|
// to whom the Software is furnished to do so, subject to the following conditions: |
|
// |
|
// The above copyright notice and this permission notice shall be included in all copies or |
|
// substantial portions of the Software. |
|
// |
|
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, |
|
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR |
|
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE |
|
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR |
|
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER |
|
// DEALINGS IN THE SOFTWARE. |
|
|
|
using System.Diagnostics; |
|
using System.Linq; |
|
using ICSharpCode.Decompiler.FlowAnalysis; |
|
using ICSharpCode.Decompiler.IL.Transforms; |
|
using ICSharpCode.Decompiler.Util; |
|
|
|
namespace ICSharpCode.Decompiler.IL.ControlFlow |
|
{ |
|
/// <summary> |
|
/// Detects 'if' structure and other non-loop aspects of control flow. |
|
/// </summary> |
|
/// <remarks> |
|
/// Order dependency: should run after loop detection. |
|
/// Blocks should be basic blocks prior to this transform. |
|
/// After this transform, they will be extended basic blocks. |
|
/// </remarks> |
|
public class ConditionDetection : IBlockTransform |
|
{ |
|
BlockTransformContext context; |
|
BlockContainer currentContainer; |
|
|
|
/// <summary> |
|
/// Builds structured control flow for the block associated with the control flow node. |
|
/// </summary> |
|
/// <remarks> |
|
/// After a block was processed, it should use structured control flow |
|
/// and have just a single 'regular' exit point (last branch instruction in the block) |
|
/// </remarks> |
|
public void Run(Block block, BlockTransformContext context) |
|
{ |
|
this.context = context; |
|
this.currentContainer = (BlockContainer)block.Parent; |
|
|
|
// We only embed blocks into this block if they aren't referenced anywhere else, |
|
// so those blocks are dominated by this block. |
|
// BlockILTransform thus guarantees that the blocks being embedded are already |
|
// fully processed. |
|
|
|
var cfgNode = context.ControlFlowNode; |
|
Debug.Assert(cfgNode.UserData == block); |
|
|
|
// Because this transform runs at the beginning of the block transforms, |
|
// we know that `block` is still a (non-extended) basic block. |
|
|
|
// Last instruction is one with unreachable endpoint |
|
// (guaranteed by combination of BlockContainer and Block invariants) |
|
Debug.Assert(block.Instructions.Last().HasFlag(InstructionFlags.EndPointUnreachable)); |
|
|
|
ILInstruction exitInst = block.Instructions.Last(); |
|
|
|
// Previous-to-last instruction might have conditional control flow, |
|
// usually an IfInstruction with a branch: |
|
IfInstruction ifInst = block.Instructions.SecondToLastOrDefault() as IfInstruction; |
|
if (ifInst != null && ifInst.FalseInst.OpCode == OpCode.Nop) { |
|
HandleIfInstruction(cfgNode, block, ifInst, ref exitInst); |
|
} |
|
if (IsUsableBranchToChild(cfgNode, exitInst)) { |
|
// "...; goto usableblock;" |
|
// -> embed target block in this block |
|
context.Step("Inline target block of unconditional branch", exitInst); |
|
var targetBlock = ((Branch)exitInst).TargetBlock; |
|
Debug.Assert(exitInst == block.Instructions.Last()); |
|
block.Instructions.RemoveAt(block.Instructions.Count - 1); |
|
block.Instructions.AddRange(targetBlock.Instructions); |
|
targetBlock.Remove(); |
|
} |
|
} |
|
|
|
private void HandleIfInstruction(ControlFlowNode cfgNode, Block block, IfInstruction ifInst, ref ILInstruction exitInst) |
|
{ |
|
if (ShouldSwapIfTargets(ifInst.TrueInst, exitInst)) { |
|
// "if (c) goto lateBlock; goto earlierBlock;" |
|
// -> "if (!c)" goto earlierBlock; goto lateBlock; |
|
// This reordering should make the if structure correspond more closely to the original C# source code |
|
context.Step("Negate if", ifInst); |
|
block.Instructions[block.Instructions.Count - 1] = ifInst.TrueInst; |
|
ifInst.TrueInst = exitInst; |
|
exitInst = block.Instructions.Last(); |
|
ifInst.Condition = Comp.LogicNot(ifInst.Condition); |
|
} |
|
|
|
ILInstruction trueExitInst; |
|
if (IsUsableBranchToChild(cfgNode, ifInst.TrueInst)) { |
|
// "if (...) goto targetBlock; exitInst;" |
|
// -> "if (...) { targetBlock } exitInst;" |
|
context.Step("Inline block as then-branch", ifInst); |
|
var targetBlock = ((Branch)ifInst.TrueInst).TargetBlock; |
|
// The targetBlock was already processed, we can embed it into the if statement: |
|
targetBlock.Remove(); |
|
ifInst.TrueInst = targetBlock; |
|
ILInstruction nestedCondition, nestedTrueInst; |
|
while (targetBlock.Instructions.Count > 0 |
|
&& targetBlock.Instructions[0].MatchIfInstruction(out nestedCondition, out nestedTrueInst)) |
|
{ |
|
nestedTrueInst = UnpackBlockContainingOnlyBranch(nestedTrueInst); |
|
if (DetectExitPoints.CompatibleExitInstruction(exitInst, nestedTrueInst)) { |
|
// "if (...) { if (nestedCondition) goto exitPoint; ... } goto exitPoint;" |
|
// -> "if (... && !nestedCondition) { ... } goto exitPoint;" |
|
context.Step("Combine 'if (cond1 && !cond2)' in then-branch", ifInst); |
|
ifInst.Condition = IfInstruction.LogicAnd(ifInst.Condition, Comp.LogicNot(nestedCondition)); |
|
targetBlock.Instructions.RemoveAt(0); |
|
// Update targetBlock label now that we've removed the first instruction |
|
if (targetBlock.Instructions.FirstOrDefault()?.ILRange.IsEmpty == false) { |
|
int offset = targetBlock.Instructions[0].ILRange.Start; |
|
targetBlock.ILRange = new Interval(offset, offset); |
|
} |
|
continue; // try to find more nested conditions |
|
} |
|
if (nestedTrueInst is Block nestedTrueBlock |
|
&& DetectExitPoints.CompatibleExitInstruction(exitInst, nestedTrueBlock.Instructions.Last()) |
|
&& targetBlock.HasFlag(InstructionFlags.EndPointUnreachable)) |
|
{ |
|
// "if (...) { if (nestedCondition) { trueInst...; goto exitPoint; } falseInst...; } goto exitPoint;" |
|
// -> "if (...) { if (!nestedCondition) { falseInst...; } trueInst... } goto exitPoint;" |
|
// (only if end-point of 'falseInst...' is unreachable) |
|
context.Step("Invert nested condition to reduce number of gotos", ifInst); |
|
var nestedIfInst = (IfInstruction)targetBlock.Instructions[0]; |
|
nestedIfInst.Condition = Comp.LogicNot(nestedCondition); |
|
nestedTrueBlock.Instructions.RemoveAt(nestedTrueBlock.Instructions.Count - 1); // remove nested goto exitPoint; |
|
// remove falseInsts from outer block |
|
var falseInsts = targetBlock.Instructions.Skip(1).ToArray(); |
|
targetBlock.Instructions.RemoveRange(1, targetBlock.Instructions.Count - 1); |
|
// add trueInsts to outer block |
|
targetBlock.Instructions.AddRange(nestedTrueBlock.Instructions); |
|
// add falseInsts to inner block |
|
nestedTrueBlock.Instructions.ReplaceList(falseInsts); |
|
nestedIfInst.Condition.AcceptVisitor(new ExpressionTransforms { context = new StatementTransformContext(context) }); |
|
} |
|
break; |
|
} |
|
|
|
trueExitInst = targetBlock.Instructions.LastOrDefault(); |
|
if (DetectExitPoints.CompatibleExitInstruction(exitInst, trueExitInst)) { |
|
// "if (...) { ...; goto exitPoint } goto exitPoint;" |
|
// -> "if (...) { ... } goto exitPoint;" |
|
context.Step("Remove redundant 'goto exitPoint;' in then-branch", ifInst); |
|
targetBlock.Instructions.RemoveAt(targetBlock.Instructions.Count - 1); |
|
trueExitInst = null; |
|
if (targetBlock.Instructions.Count == 1 && targetBlock.Instructions[0].MatchIfInstruction(out nestedCondition, out nestedTrueInst)) { |
|
// "if (...) { if (nestedCondition) nestedTrueInst; } exitInst;" |
|
// --> "if (... && nestedCondition) nestedTrueInst; } exitInst" |
|
context.Step("Combine if conditions into logic.and (in then-branch)", ifInst); |
|
ifInst.Condition = IfInstruction.LogicAnd(ifInst.Condition, nestedCondition); |
|
ifInst.TrueInst = nestedTrueInst; |
|
trueExitInst = (nestedTrueInst as Block)?.Instructions.LastOrDefault(); |
|
} |
|
} |
|
} else { |
|
trueExitInst = ifInst.TrueInst; |
|
} |
|
if (IsUsableBranchToChild(cfgNode, exitInst)) { |
|
var targetBlock = ((Branch)exitInst).TargetBlock; |
|
var falseExitInst = targetBlock.Instructions.LastOrDefault(); |
|
if (DetectExitPoints.CompatibleExitInstruction(trueExitInst, falseExitInst)) { |
|
// if (...) { ...; goto exitPoint; } goto nextBlock; nextBlock: ...; goto exitPoint; |
|
// -> if (...) { ... } else { ... } goto exitPoint; |
|
|
|
// the else block is not empty or nop-only: |
|
if (targetBlock.Children.Any(inst => !(inst is Nop) && inst != falseExitInst)) { |
|
context.Step("Inline block as else-branch", ifInst); |
|
targetBlock.Instructions.RemoveAt(targetBlock.Instructions.Count - 1); |
|
targetBlock.Remove(); |
|
ifInst.FalseInst = targetBlock; |
|
} else { |
|
// the else block is empty or nop-only and can be safely removed: |
|
context.Step("Remove empty else-branch", ifInst); |
|
targetBlock.Instructions.RemoveAt(targetBlock.Instructions.Count - 1); |
|
targetBlock.Remove(); |
|
} |
|
exitInst = block.Instructions[block.Instructions.Count - 1] = falseExitInst; |
|
Block trueBlock = ifInst.TrueInst as Block; |
|
if (trueBlock != null) { |
|
Debug.Assert(trueExitInst == trueBlock.Instructions.Last()); |
|
trueBlock.Instructions.RemoveAt(trueBlock.Instructions.Count - 1); |
|
} else { |
|
Debug.Assert(trueExitInst == ifInst.TrueInst); |
|
ifInst.TrueInst = new Nop { ILRange = ifInst.TrueInst.ILRange }; |
|
} |
|
} |
|
} |
|
if (IsEmpty(ifInst.TrueInst)) { |
|
// prefer empty true-branch to empty-else branch |
|
context.Step("Swap empty then-branch with else-branch", ifInst); |
|
var oldTrue = ifInst.TrueInst; |
|
ifInst.TrueInst = ifInst.FalseInst; |
|
ifInst.FalseInst = new Nop { ILRange = oldTrue.ILRange }; |
|
ifInst.Condition = Comp.LogicNot(ifInst.Condition); |
|
|
|
// After swapping, it's possible that we can introduce a short-circuit operator: |
|
Block trueBlock = ifInst.TrueInst as Block; |
|
ILInstruction nestedCondition, nestedTrueInst; |
|
if (trueBlock != null && trueBlock.Instructions.Count == 1 |
|
&& trueBlock.FinalInstruction is Nop |
|
&& trueBlock.Instructions[0].MatchIfInstruction(out nestedCondition, out nestedTrueInst)) { |
|
// if (cond) if (nestedCond) nestedTrueInst |
|
// ==> if (cond && nestedCond) nestedTrueInst |
|
context.Step("Combine if conditions into logic.and (after branch swapping)", ifInst); |
|
ifInst.Condition = IfInstruction.LogicAnd(ifInst.Condition, nestedCondition); |
|
ifInst.TrueInst = nestedTrueInst; |
|
} |
|
} else if (ifInst.FalseInst.OpCode != OpCode.Nop && ifInst.FalseInst.ILRange.Start < ifInst.TrueInst.ILRange.Start) { |
|
// swap true and false branches of if/else construct, |
|
// to bring them in the same order as the IL code |
|
context.Step("Swap then-branch with else-branch", ifInst); |
|
var oldTrue = ifInst.TrueInst; |
|
ifInst.TrueInst = ifInst.FalseInst; |
|
ifInst.FalseInst = oldTrue; |
|
ifInst.Condition = Comp.LogicNot(ifInst.Condition); |
|
} |
|
} |
|
|
|
static bool IsEmpty(ILInstruction inst) |
|
{ |
|
var block = inst as Block; |
|
return block != null && block.Instructions.Count == 0 && block.FinalInstruction is Nop |
|
|| inst is Nop; |
|
} |
|
|
|
private ILInstruction UnpackBlockContainingOnlyBranch(ILInstruction inst) |
|
{ |
|
Block block = inst as Block; |
|
if (block != null && block.Instructions.Count == 1 && block.FinalInstruction is Nop && IsBranchOrLeave(block.Instructions[0])) |
|
return block.Instructions.Single(); |
|
else |
|
return inst; |
|
} |
|
|
|
bool ShouldSwapIfTargets(ILInstruction inst1, ILInstruction inst2) |
|
{ |
|
Block block1 = null, block2 = null; |
|
if (inst1.MatchBranch(out block1) && inst2.MatchBranch(out block2)) { |
|
// prefer arranging stuff in IL order |
|
return block1.ILRange.Start > block2.ILRange.Start; |
|
} |
|
BlockContainer container1, container2; |
|
if (inst1.MatchLeave(out container1) && container1.Parent is TryInstruction) { |
|
// 'leave tryBlock' is considered to have a later target than |
|
// any branch within the container, and also a later target |
|
// than a return instruction. |
|
// This is necessary to avoid "goto" statements in the |
|
// ExceptionHandling.ConditionalReturnInThrow test. |
|
if (!inst2.MatchLeave(out container2)) |
|
container2 = block2?.Parent as BlockContainer; |
|
return container2 == null || container2.IsDescendantOf(container1); |
|
} |
|
if (inst1.MatchBranch(out block1) && inst2.MatchLeave(out container2) |
|
&& block1.IncomingEdgeCount > 1) |
|
{ |
|
// if (..) goto x; leave c; |
|
// Unless x can be inlined, it's better to swap the order if the 'leave' |
|
// has a chance to turn into a 'break;' or 'return;' |
|
if (container2.Parent is ILFunction) { |
|
return true; // return |
|
} |
|
if (container2.EntryPoint.IncomingEdgeCount > 1) { |
|
// break |
|
return BlockContainer.FindClosestContainer(inst2) == container2; |
|
} |
|
} |
|
return false; |
|
} |
|
|
|
/// <summary> |
|
/// Gets whether <c>potentialBranchInstruction</c> is a branch to a block |
|
/// that is dominated by <c>cfgNode</c>. |
|
/// If this function returns true, we replace the branch instruction with the block itself. |
|
/// </summary> |
|
bool IsUsableBranchToChild(ControlFlowNode cfgNode, ILInstruction potentialBranchInstruction) |
|
{ |
|
Branch br = potentialBranchInstruction as Branch; |
|
if (br == null) |
|
return false; |
|
var targetBlock = br.TargetBlock; |
|
return targetBlock.Parent == currentContainer |
|
&& targetBlock.IncomingEdgeCount == 1 && targetBlock.FinalInstruction.OpCode == OpCode.Nop |
|
&& cfgNode.Dominates(context.ControlFlowGraph.GetNode(targetBlock)); |
|
} |
|
|
|
private bool IsBranchOrLeave(ILInstruction inst) |
|
{ |
|
switch (inst) { |
|
case Branch branch: |
|
return true; |
|
case Leave leave: |
|
// only void returns are supported as 'exit points' |
|
return leave.Value.MatchNop(); |
|
default: |
|
return false; |
|
} |
|
} |
|
} |
|
}
|
|
|