[X86] Fix checks for illegal physreg COPY instructions

[foad]

Summary

D105263 changed this test to not expect a MachineVerifier error on this
instruction:

; FP16 reg is sub_reg of xmm
%0:_(s16) = COPY $xmm0

D107082 changed the behaviour back again so that this instruction did
cause an error, but the test was not updated to expect the error.

[pengfei]

LGTM. Maybe update the description with more background.

The test case was indeed passed with D105263 but then failed since D107082 https://godbolt.org/z/x4nq5bcWo
D107082 changed the stack size of FR16(X) from 16 to 32 to workaround spill/reload problems. But seems it affects the COPY verification here.

llvm/test/MachineVerifier/test_copy_physregs_x86.mir

-#RUN: not --crash llc -march=x86-64 -run-pass=none -verify-machineinstrs -o /dev/null %s 2>&1 | FileCheck %s
+# RUN: not --crash llc -march=x86-64 -run-pass=none -verify-machineinstrs -o /dev/null %s 2>&1 | FileCheck %s -implicit-check-not="Bad machine code"
 # REQUIRES: x86-registered-target
 
 # These copies have mismatched type sizes that are allowed because the
 # register class is defined to directly include the narrower type.
 ---
 name:            test_valid_copies
 tracksRegLiveness: true
 body:             |

 
 ---
 name:            test_invalid_copies
 tracksRegLiveness: true
 body:             |
   bb.0:
     liveins: $xmm0, $xmm1, $xmm2, $xmm3
 
-    ; FP16 reg is sub_reg of xmm
+    ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: %0:_(s16) = COPY $xmm0
     %0:_(s16) = COPY $xmm0
 
     ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: %1:_(<4 x s16>) = COPY $xmm1
     %1:_(<4 x s16>) = COPY $xmm1
 
     ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: %2:_(s256) = COPY $xmm2
     %2:_(s256) = COPY $xmm2
 
     ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: %3:_(<8 x s32>) = COPY $xmm3
     %3:_(<8 x s32>) = COPY $xmm3
 
-    ; FP16 reg is sub_reg of xmm
+    ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: $xmm0 = COPY %0:_(s16)
     $xmm0 = COPY %0
 
     ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: $xmm1 = COPY %1:_(<4 x s16>)
     $xmm1 = COPY %1
 
     ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: $xmm2 = COPY %2:_(s256)
     $xmm2 = COPY %2
 
     ; CHECK: *** Bad machine code: Copy Instruction is illegal with mismatching sizes ***
+    ; CHECK: - instruction: $xmm3 = COPY %3:_(<8 x s32>)
     $xmm3 = COPY %3
 ...