Adjustments from code review

Two adjustments for things that arose during code review:

(1) Now using static local functions instead of non-static ones.

(2) Removed InstructionHelpers class and reverted to straightforward
    ways of checking for instruction types.

Author: alexthornton1

src/coverlet.core/Extensions/InstructionExtensions.cs

@@ -451,7 +451,7 @@ private static bool SkipGeneratedBranchesForAwaitForeach(List<Instruction> instr
             // if GetResult() returned true.
 
 
-            bool CheckForAsyncEnumerator(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool CheckForAsyncEnumerator(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // We're looking for the following pattern, which checks whether a
                 // compiler-generated field of type IAsyncEnumerator<> is null.
@@ -467,7 +467,8 @@ bool CheckForAsyncEnumerator(List<Instruction> instructions, Instruction instruc
                 }
 
                 if (currentIndex >= 2 &&
-                    instructions[currentIndex - 2].IsLdarg(0) &&
+                    (instructions[currentIndex - 2].OpCode == OpCodes.Ldarg ||
+                     instructions[currentIndex - 2].OpCode == OpCodes.Ldarg_0) &&
                     instructions[currentIndex - 1].OpCode == OpCodes.Ldfld &&
                     instructions[currentIndex - 1].Operand is FieldDefinition field &&
                     IsCompilerGenerated(field) && field.FieldType.FullName.StartsWith("System.Collections.Generic.IAsyncEnumerator"))
@@ -479,7 +480,7 @@ bool CheckForAsyncEnumerator(List<Instruction> instructions, Instruction instruc
             }
 
 
-            bool CheckIfExceptionThrown(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool CheckIfExceptionThrown(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // Here, we want to find a pattern where we're checking whether a
                 // compiler-generated field of type Object is null.  To narrow our
@@ -537,7 +538,7 @@ instructions[j].Operand is MethodReference callRef &&
             }
 
 
-            bool CheckThrownExceptionType(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool CheckThrownExceptionType(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // In this case, we're looking for a branch generated by the compiler to
                 // check whether a previously-thrown exception has (at least) the type
@@ -567,7 +568,12 @@ bool CheckThrownExceptionType(List<Instruction> instructions, Instruction instru
                     if (instructions[i].OpCode == OpCodes.Isinst &&
                         instructions[i].Operand is TypeReference typeRef &&
                         typeRef.FullName == "System.Exception" &&
-                        instructions[i - 1].IsLdloc())
+                        (instructions[i - 1].OpCode == OpCodes.Ldloc ||
+                         instructions[i - 1].OpCode == OpCodes.Ldloc_S ||
+                         instructions[i - 1].OpCode == OpCodes.Ldloc_0 ||
+                         instructions[i - 1].OpCode == OpCodes.Ldloc_1 ||
+                         instructions[i - 1].OpCode == OpCodes.Ldloc_2 ||
+                         instructions[i - 1].OpCode == OpCodes.Ldloc_3))
                     {
                         return true;
                     }
@@ -585,7 +591,7 @@ private static bool SkipGeneratedBranchesForAwaitUsing(List<Instruction> instruc
                    CheckForCleanup(instructions, instruction, currentIndex);
 
 
-            bool CheckForSkipDisposal(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool CheckForSkipDisposal(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // The async state machine generated for an "await using" contains a branch
                 // that checks whether the call to DisposeAsync() needs to be skipped.
@@ -654,9 +660,18 @@ instructions[i].Operand is FieldDefinition reloadedField &&
                         }
                     }
                 }
-                else if (instructions[currentIndex - 1].IsLdloc(out int localVariableIndex) &&
-                         instructions[currentIndex + 1].IsLdloc(out int reloadedLocalVariableIndex) &&
-                         localVariableIndex == reloadedLocalVariableIndex &&
+                else if ((instructions[currentIndex - 1].OpCode == OpCodes.Ldloc ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_S ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_0 ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_1 ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_2 ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_3) &&
+                         (instructions[currentIndex + 1].OpCode == OpCodes.Ldloc ||
+                          instructions[currentIndex + 1].OpCode == OpCodes.Ldloc_S ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_0 ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_1 ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_2 ||
+                          instructions[currentIndex - 1].OpCode == OpCodes.Ldloc_3) &&
                          instructions[currentIndex + 2].OpCode == OpCodes.Callvirt &&
                          instructions[currentIndex + 2].Operand is MethodReference method &&
                          method.DeclaringType.FullName == "System.IAsyncDisposable" &&
@@ -686,7 +701,7 @@ instructions[i].Operand is FieldDefinition reloadedField &&
             }
 
 
-            bool CheckForCleanup(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool CheckForCleanup(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // The pattern we're looking for here is this:
                 //
@@ -721,7 +736,8 @@ bool CheckForCleanup(List<Instruction> instructions, Instruction instruction, in
                 }
 
                 if (currentIndex >= 1 &&
-                    instructions[currentIndex - 1].IsLdc_I4(1))
+                    (instructions[currentIndex - 1].OpCode == OpCodes.Ldc_I4 ||
+                     instructions[currentIndex - 1].OpCode == OpCodes.Ldc_I4_1))
                 {
                     int minLoadFieldIndex = Math.Max(1, currentIndex - 5);
 
@@ -770,7 +786,7 @@ private static bool SkipGeneratedBranchesForAsyncIterator(List<Instruction> inst
                    DisposeCheck(instructions, instruction, currentIndex);
 
 
-            bool CheckForStateSwitch(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool CheckForStateSwitch(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // The pattern we're looking for here is this one:
                 //
@@ -813,7 +829,7 @@ instructions[i].Operand is FieldDefinition field &&
             }
 
 
-            bool DisposeCheck(List<Instruction> instructions, Instruction instruction, int currentIndex)
+            static bool DisposeCheck(List<Instruction> instructions, Instruction instruction, int currentIndex)
             {
                 // Within the compiler-generated async iterator, there are at least a
                 // couple of places where we find this pattern, in which the async