From 44bb5861cb2e8ee60ca4d251c8dbfb25c500f029 Mon Sep 17 00:00:00 2001
From: Dongbo Wang <dongbow@microsoft.com>
Date: Fri, 21 Aug 2020 10:28:16 -0700
Subject: [PATCH] Avoid multiple enumerations of an `IEnumerable<Expression>`
 instance in `Compiler.cs` (#13491)

---
 .../engine/parser/Compiler.cs                 | 32 ++++++++++++++++---
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/src/System.Management.Automation/engine/parser/Compiler.cs b/src/System.Management.Automation/engine/parser/Compiler.cs
index 3a25e8c5d9..642bd1e1dc 100644
--- a/src/System.Management.Automation/engine/parser/Compiler.cs
+++ b/src/System.Management.Automation/engine/parser/Compiler.cs
@@ -949,9 +949,20 @@ namespace System.Management.Automation.Language
             return result;
         }
 
-        private IEnumerable<Expression> CompileInvocationArguments(IEnumerable<ExpressionAst> arguments)
+        private IEnumerable<Expression> CompileInvocationArguments(IReadOnlyList<ExpressionAst> arguments)
         {
-            return arguments == null ? Array.Empty<Expression>() : arguments.Select(CompileExpressionOperand);
+            if (arguments is null || arguments.Count == 0)
+            {
+                return Array.Empty<Expression>();
+            }
+
+            var result = new Expression[arguments.Count];
+            for (int i = 0; i < result.Length; i++)
+            {
+                result[i] = CompileExpressionOperand(arguments[i]);
+            }
+
+            return result;
         }
 
         internal Expression ReduceAssignment(ISupportsAssignment left, TokenKind tokenKind, Expression right)
@@ -6669,9 +6680,20 @@ namespace System.Management.Automation.Language
                 return _argExprTemps;
             }
 
-            return InvokeMemberExpressionAst.Arguments == null
-               ? Array.Empty<Expression>()
-               : InvokeMemberExpressionAst.Arguments.Select(compiler.Compile).ToArray();
+            ReadOnlyCollection<ExpressionAst> arguments = InvokeMemberExpressionAst.Arguments;
+
+            if (arguments is null || arguments.Count == 0)
+            {
+                return Array.Empty<Expression>();
+            }
+
+            var result = new Expression[arguments.Count];
+            for (int i = 0; i < result.Length; i++)
+            {
+                result[i] = compiler.Compile(arguments[i]);
+            }
+
+            return result;
         }
 
         public Expression GetValue(Compiler compiler, List<Expression> exprs, List<ParameterExpression> temps)