[NFC][AMDGPU] Pre-commit a test case of checking register coalescer on v_pk_mov_b32 (#127715)

This PR serves as a preliminary step, adding a test case for register coalescer on v_pk_mov_b32. It is intended to demonstrate the code changes introduced in an upcoming PR.

Author: shiltian

llvm/test/CodeGen/AMDGPU/vgpr-remat-v_pk_mov_b32.mir

@@ -0,0 +1,49 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx942 -run-pass=register-coalescer -o - %s | FileCheck %s
+
+---
+name: test_remat_v_pk_mov_b32
+tracksRegLiveness: true
+body: |
+  ; CHECK-LABEL: name: test_remat_v_pk_mov_b32
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.2(0x40000000), %bb.1(0x40000000)
+  ; CHECK-NEXT:   liveins: $sgpr0
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[V_PK_MOV_B32_:%[0-9]+]]:vreg_64_align2 = V_PK_MOV_B32 8, 0, 8, 0, 0, 0, 0, 0, 0, implicit $exec
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:vreg_64_align2 = COPY [[V_PK_MOV_B32_]]
+  ; CHECK-NEXT:   [[COPY1:%[0-9]+]]:vreg_64_align2 = COPY [[V_PK_MOV_B32_]]
+  ; CHECK-NEXT:   [[COPY2:%[0-9]+]]:sreg_64 = COPY $sgpr0
+  ; CHECK-NEXT:   $exec = S_MOV_B64_term [[COPY2]]
+  ; CHECK-NEXT:   S_CBRANCH_EXECZ %bb.2, implicit $exec
+  ; CHECK-NEXT:   S_BRANCH %bb.1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors: %bb.2(0x80000000)
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:vreg_64_align2 = V_PK_ADD_F32 8, [[COPY]], 8, [[COPY]], 11, 0, 0, 0, 0, implicit $mode, implicit $exec
+  ; CHECK-NEXT:   [[COPY1:%[0-9]+]]:vreg_64_align2 = V_PK_ADD_F32 8, [[COPY1]], 8, [[COPY1]], 11, 0, 0, 0, 0, implicit $mode, implicit $exec
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2:
+  ; CHECK-NEXT:   S_NOP 0, implicit [[COPY]]
+  ; CHECK-NEXT:   S_NOP 0, implicit [[COPY1]]
+  ; CHECK-NEXT:   S_ENDPGM 0, implicit [[V_PK_MOV_B32_]]
+  bb.0:
+    liveins: $sgpr0
+    %0:vreg_64_align2 = V_PK_MOV_B32 8, 0, 8, 0, 0, 0, 0, 0, 0, implicit $exec
+    %1:vreg_64_align2 = COPY %0:vreg_64_align2
+    %2:vreg_64_align2 = COPY %0:vreg_64_align2
+    %3:sreg_64 = COPY $sgpr0
+    $exec = S_MOV_B64_term %3:sreg_64
+    S_CBRANCH_EXECZ %bb.2, implicit $exec
+    S_BRANCH %bb.1
+
+  bb.1:
+    %1:vreg_64_align2 = V_PK_ADD_F32 8, %1, 8, %1, 11, 0, 0, 0, 0, implicit $mode, implicit $exec
+    %2:vreg_64_align2 = V_PK_ADD_F32 8, %2, 8, %2, 11, 0, 0, 0, 0, implicit $mode, implicit $exec
+
+  bb.2:
+    S_NOP 0, implicit %1
+    S_NOP 0, implicit %2
+    S_ENDPGM 0, implicit %0
+...