[Loops] Detect simple for loops in ILAst as well.

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -316,18 +316,30 @@ namespace ICSharpCode.Decompiler.CSharp
 					blockStatement = ConvertAsBlock(loop.Body);
 					if (!loop.Body.HasFlag(InstructionFlags.EndPointUnreachable))
 						blockStatement.Add(new BreakStatement());
+					Statement iterator = null;
+					if (loop.IncrementBlock == null) {
+						// increment check is done by DetectLoop
+						var statement = blockStatement.Last();
+						while (statement is ContinueStatement)
+							statement = (Statement)statement.PrevSibling;
+						iterator = statement.Detach();
+					}
 					var forBody = ConvertBlockContainer(blockStatement, container, loop.AdditionalBlocks, true);
 					var forStmt = new ForStatement() {
 						Condition = conditionExpr,
 						EmbeddedStatement = forBody
 					};
-					for (int i = 0; i < loop.IncrementBlock.Instructions.Count - 1; i++) {
-						forStmt.Iterators.Add(Convert(loop.IncrementBlock.Instructions[i]));
-					}
-					if (loop.IncrementBlock.IncomingEdgeCount > continueCount)
-						forBody.Add(new LabelStatement { Label = loop.IncrementBlock.Label });
 					if (forBody.LastOrDefault() is ContinueStatement continueStmt2)
 						continueStmt2.Remove();
+					if (loop.IncrementBlock != null) {
+						for (int i = 0; i < loop.IncrementBlock.Instructions.Count - 1; i++) {
+							forStmt.Iterators.Add(Convert(loop.IncrementBlock.Instructions[i]));
+						}
+						if (loop.IncrementBlock.IncomingEdgeCount > continueCount)
+							forBody.Add(new LabelStatement { Label = loop.IncrementBlock.Label });
+					} else if (iterator != null) {
+						forStmt.Iterators.Add(iterator.Detach());
+					}
 					return forStmt;
 				default:
 				case LoopKind.While:

ICSharpCode.Decompiler/IL/DetectedLoop.cs

@@ -34,6 +34,7 @@ namespace ICSharpCode.Decompiler.IL
 		public Block ContinueJumpTarget { get; private set; } // jumps to this block are "continue;" jumps
 		public ILInstruction Body { get; private set; }       // null in case of DoWhile
 		public Block[] AdditionalBlocks { get; private set; } // blocks to be merged into the loop body
+		public ILVariable IncrementTarget { get; private set; } // null, except in case of For
 
 		private DetectedLoop(BlockContainer container)
 		{
@@ -106,7 +107,20 @@ namespace ICSharpCode.Decompiler.IL
 				if (IncrementBlock != null) {
 					// for-loop
 					Kind = LoopKind.For;
+					if (IncrementBlock.Instructions[0] is StLoc increment)
+						IncrementTarget = increment.Variable;
 					AdditionalBlocks = Container.Blocks.Skip(1).Where(b => b != IncrementBlock).ToArray();
+				} else if (trueInst is Block block) {
+					var variable = GetVariableFromCondition(conditionInst);
+					var last = block.Instructions.LastOrDefault();
+					var secondToLast = block.Instructions.SecondToLastOrDefault();
+					if (variable != null && last != null && secondToLast != null && last.MatchBranch(Container.EntryPoint) && MatchIncrement(secondToLast, variable)) {
+						Kind = LoopKind.For;
+						IncrementTarget = variable;
+						AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
+					} else {
+						AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
+					}
 				} else {
 					AdditionalBlocks = Container.Blocks.Skip(1).ToArray();
 				}
@@ -126,5 +140,23 @@ namespace ICSharpCode.Decompiler.IL
 			}
 			return this;
 		}
+
+		static ILVariable GetVariableFromCondition(ILInstruction conditionInst)
+		{
+			var ldLocs = conditionInst.Children.OfType<LdLoc>().ToArray();
+			if (ldLocs.Length == 1)
+				return ldLocs[0].Variable;
+			else
+				return null;
+		}
+
+		static bool MatchIncrement(ILInstruction inst, ILVariable variable)
+		{
+			if (!inst.MatchStLoc(variable, out var value))
+				return false;
+			if (!value.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out var left, out var right))
+				return false;
+			return left.MatchLdLoc(variable) && right.MatchLdcI(out var val) && val == 1;
+		}
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -147,22 +147,9 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				foreach (BlockContainer possibleLoop in methodBody.Descendants.OfType<BlockContainer>().Reverse()) {
 					if (possibleLoop.EntryPoint.IncomingEdgeCount == 1) continue;
 					var loop = DetectedLoop.DetectLoop(possibleLoop);
-					if (loop.Kind != LoopKind.For) continue;
-					var condition = loop.Conditions?[0];
-					while (condition is LogicNot not)
-						condition = not.Argument;
-					if (condition is Comp comp) {
-						switch (comp.Kind) {
-							case ComparisonKind.GreaterThan:
-							case ComparisonKind.GreaterThanOrEqual:
-							case ComparisonKind.LessThan:
-							case ComparisonKind.LessThanOrEqual:
-								if (comp.Left.MatchLdLoc(variable)) {
-									isLoopCounter = true;
-								}
-								break;
-						}
-					}
+					if (loop.Kind != LoopKind.For || loop.IncrementTarget == null) continue;
+					if (loop.IncrementTarget == variable)
+						isLoopCounter = true;
 				}
 				if (isLoopCounter) {
 					// For loop variables, use i,j,k,l,m,n