Miscompilation of a switch case

System information

System:    Kernel: 5.11.0-18-generic x86_64 bits: 64 compiler: gcc v: 10.2.1 Desktop: GNOME 3.38.4 
           tk: GTK 3.24.25 wm: gnome-shell dm: GDM3 Distro: Ubuntu 21.04 (Hirsute Hippo) 
CPU:       Info: 6-Core model: Intel Core i7-8750H bits: 64 type: MT MCP arch: Kaby Lake note: check rev: A L2 cache: 9 MiB 
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 52799 
           Speed: 900 MHz min/max: 800/4100 MHz Core speeds (MHz): 1: 900 2: 900 3: 900 4: 900 5: 900 6: 900 7: 900 8: 901 
           9: 900 10: 900 11: 900 12: 900 
Graphics:  Device-1: Intel CoffeeLake-H GT2 [UHD Graphics 630] vendor: ASUSTeK driver: i915 v: kernel bus ID: 00:02.0 
           chip ID: 8086:3e9b 
           Device-2: NVIDIA GP107M [GeForce GTX 1050 Ti Mobile] vendor: ASUSTeK driver: nvidia v: 460.80 bus ID: 01:00.0 
           chip ID: 10de:1c8c 
           Display: x11 server: X.Org 1.20.11 compositor: gnome-shell driver: loaded: modesetting,nvidia 
           unloaded: fbdev,nouveau,vesa resolution: 1: 1920x1080~120Hz 2: 1920x1080~60Hz s-dpi: 96
           OpenGL: renderer: llvmpipe (LLVM 12.0.0 256 bits) v: 4.5 Mesa 21.1.5 compat-v: 3.1 direct render: Yes 

Describe the issue

The side-effecting instruction of the following switch does not seem to be executed.

#version 450
layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
layout(std430, binding = 0) buffer buffer_0 {
 int ext_0; // 0
 int ext_1; // 5
 int ext_2; // 0
} ;
void main()
{
  ext_0 += ext_1; // ext_0 = 5
  switch(ext_1 ^= ext_0) // ext_0 = 5 ^ 5 = 0
  {
    case 0:
      ext_2 = 1;
      break;
    case 5:
      ext_2 = 2;
      break;
  }
}

At the end of the execution, the shader storage block contains:

5 5 2

I would expect the shader storage block to contain instead:

5 0 1

Reproducing the issue

The shader has been found using a testing tool called Shadertrap. Instructions are given below to reproduce it with that tool. A shader_test is also attached for convenience. shader04.shader_test

1. Get or build Shadertrap:
   1. A build version of Shadertrap for linux can be found on Shadertrap release repository.
   2. To build from source, please refer to Shadertrap repository
2. Ge the shader file shader04.shadertrap
3. Execute the Shadertrap command

bin/shadertrap shader04.shadertrap

4. Collect the buffer results in the execution folder (one file per buffer)