[XamlC] remove unused variables (#620)

1 files changed, 34 insertions, 1 deletions

diff --git a/Xamarin.Forms.Build.Tasks/MethodBodyExtensions.cs b/Xamarin.Forms.Build.Tasks/MethodBodyExtensions.cs
index 380cb59c..7db321f3 100644
--- a/Xamarin.Forms.Build.Tasks/MethodBodyExtensions.cs
+++ b/Xamarin.Forms.Build.Tasks/MethodBodyExtensions.cs
@@ -1,6 +1,8 @@
 using Mono.Cecil.Cil;
 using Mono.Cecil.Rocks;
 using System;
+using System.Linq;
+using System.Collections.Generic;
 
 namespace Xamarin.Forms.Build.Tasks
 {
@@ -13,6 +15,7 @@ namespace Xamarin.Forms.Build.Tasks
 
 			self.OptimizeLongs();
 			self.OptimizeStLdLoc();
+			self.RemoveUnusedLocals();
 			self.OptimizeMacros();
 		}
 
@@ -25,7 +28,6 @@ namespace Xamarin.Forms.Build.Tasks
 		//this can be removed if/when https://github.com/jbevain/cecil/pull/307 is released in a nuget we consume
 		static void OptimizeLongs(this MethodBody self)
 		{
-			var method = self.Method;
 			for (var i = 0; i < self.Instructions.Count; i++) {
 				var instruction = self.Instructions[i];
 				if (instruction.OpCode.Code != Code.Ldc_I8)
@@ -56,5 +58,36 @@ namespace Xamarin.Forms.Build.Tasks
 				ExpandMacro(next, OpCodes.Stloc, vardef);
 			}
 		}
+
+		static void RemoveUnusedLocals(this MethodBody self)
+		{
+			//Count ldloc for each variable
+			var ldlocUsed = new List<VariableDefinition>();
+			foreach (var instruction in self.Instructions) {
+				if (instruction.OpCode.Code != Code.Ldloc)
+					continue;
+				var varDef = (VariableDefinition)instruction.Operand;
+				if (!ldlocUsed.Contains(varDef))
+					ldlocUsed.Add(varDef);
+			}
+
+			foreach (var varDef in self.Variables.ToArray()) {
+				if (ldlocUsed.Contains(varDef))
+					continue;
+
+				//find the Stloc instruction
+				var instruction = (from instr in self.Instructions where instr.OpCode.Code == Code.Stloc && instr.Operand == varDef select instr).First();
+
+				//remove dup/stloc
+				if (instruction.Previous.OpCode.Code != Code.Dup)
+					break;
+
+				self.Instructions.Remove(instruction.Previous);
+				self.Instructions.Remove(instruction);
+
+				//and remove the variable
+				self.Variables.Remove(varDef);
+			}
+		}
 	}
 }
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