[BranchFolding][SEH] Add test to check block merge bug

Author: HaohaiWen

llvm/test/CodeGen/X86/branchfolding-landingpad-cfg.mir

@@ -49,3 +49,44 @@ body:             |
   bb.6:
     RET 0
 ...
+---
+name:            foo
+body:             |
+  ; CHECK-LABEL: name: foo
+  ; CHECK: bb.0:
+  ; CHECK-NEXT:   successors: %bb.3(0x7ffff800), %bb.1(0x00000800)
+  ; CHECK-NEXT:   liveins: $rcx
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   renamable $eax = MOV32rm renamable $rcx, 1, $noreg, 0, $noreg
+  ; CHECK-NEXT:   TEST32rr renamable $eax, renamable $eax, implicit-def $eflags
+  ; CHECK-NEXT:   JCC_1 %bb.3, 15, implicit $eflags
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1:
+  ; CHECK-NEXT:   successors:
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.2 (machine-block-address-taken, landing-pad, ehfunclet-entry):
+  ; CHECK-NEXT:   CLEANUPRET
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.3:
+  ; CHECK-NEXT:   INT 3
+  ; CHECK-NEXT:   RET 0
+  bb.0:
+    successors: %bb.1(0x7ffff800), %bb.2(0x00000800)
+    liveins: $rcx
+
+    renamable $eax = MOV32rm renamable $rcx, 1, $noreg, 0, $noreg
+    TEST32rr renamable $eax, renamable $eax, implicit-def $eflags
+    JCC_1 %bb.2, 14, implicit killed $eflags
+    JMP_1 %bb.1
+
+  bb.1:
+    successors: %bb.3(0x80000000)
+    INT 3
+
+  bb.2:
+    RET 0
+
+  bb.3 (machine-block-address-taken, landing-pad, ehfunclet-entry):
+    CLEANUPRET
+...