Blend animation and recalculate some bones' rotation?

Character has a idle animation and a shoot animation and some run animations.

Animator has 2 layer, Base is for moving, Shoot is for shooting.
Shoot layer has a upper body mask because shoot animation is for upper body.

When character stand and shoot, looks fine.



But when character run and shoot, gun strange rotate down.

Shoot animation is made for idle animation, not for run animation.
Notice upper body(3 spine bones), idle animation and run animation are different at this part.
Because two arms are spine's child, so when spine rotate, two arms have to rotate.
Different spine rotation will affect arms' blend result.
Because idle animation and run animation have different spines rotation, when blend run animation and shoot animation, strange things happen, in this case, gun rotate down instead of rotate up.

Then I got a idea, fix two arms' rotation.
1. Set animator parameter to make character back to idle state
2. Animator.Update()
3. Record two arms' rotation
4. Set animator parameter to make character restore to run state
5. Animator.Update()
6. Rewrite two arms rotation using recorded two arms' data
And here's result

This is the result I want.
But the problem is that animator need to update 2 times, which lead to a seriously performance problem.

Is there any way to reduce computation and increase performance base on my method?
Or is there any other method to get the result I want?

Thanks in advance!
Project(Unity 5.6.5f1):
http://www.mediafire.com/file/7tiazd8s5bd499s/RunShootProblem%282%29.rar/file

Code:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class PlayerBehaviour : MonoBehaviour
6. {
7.     public bool EnableBoneFix;
8.  
9.     Animator animator;
10.  
11.     Transform leftShoulder;
12.     Transform leftUpperArm;
13.     Transform leftLowerArm;
14.     Transform leftHand;
15.     Transform rightShoulder;
16.     Transform rightUpperArm;
17.     Transform rightLowerArm;
18.     Transform rightHand;
19.  
20.     void Start()
21.     {
22.         animator = GetComponent<Animator>();
23.  
24.         leftShoulder = animator.GetBoneTransform(HumanBodyBones.LeftShoulder);
25.         leftUpperArm = animator.GetBoneTransform(HumanBodyBones.LeftUpperArm);
26.         leftLowerArm = animator.GetBoneTransform(HumanBodyBones.LeftLowerArm);
27.         leftHand = animator.GetBoneTransform(HumanBodyBones.LeftHand);
28.         rightShoulder = animator.GetBoneTransform(HumanBodyBones.RightShoulder);
29.         rightUpperArm = animator.GetBoneTransform(HumanBodyBones.RightUpperArm);
30.         rightLowerArm = animator.GetBoneTransform(HumanBodyBones.RightLowerArm);
31.         rightHand = animator.GetBoneTransform(HumanBodyBones.RightHand);
32.     }
33.    
34.     void Update()
35.     {
36.         animator.SetFloat("hor", Input.GetAxis("Horizontal"));
37.         animator.SetFloat("ver", Input.GetAxis("Vertical"));
38.        
39.         if (Input.GetButtonDown("Fire1"))
40.             animator.SetTrigger("Shoot");
41.     }
42.  
43.     void LateUpdate()
44.     {
45.         if (EnableBoneFix)
46.         {
47.             //Restore to idle state
48.             float hor = animator.GetFloat("hor");
49.             float ver = animator.GetFloat("ver");
50.             animator.SetFloat("hor", 0);
51.             animator.SetFloat("ver", 0);
52.             animator.Update(0);
53.  
54.             //Record two arms' rotation
55.             Quaternion idleLeftShoulderRotation = leftShoulder.rotation;
56.             Quaternion idleLeftUpperArmRotation = leftUpperArm.rotation;
57.             Quaternion idleLeftLowerArmRotation = leftLowerArm.rotation;
58.             Quaternion idleLeftHandRotation = leftHand.rotation;
59.             Quaternion idleRightShoulderRotation = rightShoulder.rotation;
60.             Quaternion idleRightUpperArmRotation = rightUpperArm.rotation;
61.             Quaternion idleRightLowerArmRotation = rightLowerArm.rotation;
62.             Quaternion idleRightHandRotation = rightHand.rotation;
63.  
64.             //Restore back to run state
65.             animator.SetFloat("hor", hor);
66.             animator.SetFloat("ver", ver);
67.             animator.Update(0);
68.  
69.             //Make two arms acts like idle state
70.             leftShoulder.rotation = idleLeftShoulderRotation;
71.             leftUpperArm.rotation = idleLeftUpperArmRotation;
72.             leftLowerArm.rotation = idleLeftLowerArmRotation;
73.             leftHand.rotation = idleLeftHandRotation;
74.             rightShoulder.rotation = idleRightShoulderRotation;
75.             rightUpperArm.rotation = idleRightUpperArmRotation;
76.             rightLowerArm.rotation = idleRightLowerArmRotation;
77.             rightHand.rotation = idleRightHandRotation;
78.         }
79.     }
80. }
81.  

 

have you got any ideas?

 

Anyone figure this out? I think it may have something to do with the base layer affecting the initial rotation of the bones and therefore the layered animation but not sure how to get around this