Drop dso_local, comment the test

Author: s-barannikov

llvm/test/CodeGen/X86/sjlj-unwind-clobber.ll

@@ -1,8 +1,17 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
 ; RUN: llc -mtriple=x86_64 -exception-model=sjlj -o - %s | FileCheck %s
 
-declare dso_local i32 @__gxx_personality_sj0(...)
-declare dso_local preserve_allcc void @foo(ptr)
+declare i32 @__gxx_personality_sj0(...)
+declare preserve_allcc void @foo(ptr)
+
+; Check that register allocator splits live ranges of loop invariant virtual
+; registers as they don't survive the unwind edge of an invoke.
+; The argument of `foo` (passed in %rdi) and the address of the jump table
+; (base register of `jmpq`) are loop invariant. They survive the call to `foo`,
+; but are clobbered by the unwinder when `foo` throws an exception, and so
+; their live ranges must be split around the unwind edge `callq foo` -> LBB0_3.
+; This is achieved by recalculating their values before each use rather than
+; once before the loop as was the case before register allocation.
 
 define void @test() personality ptr @__gxx_personality_sj0 {
 ; CHECK-LABEL: test:
@@ -15,7 +24,8 @@ define void @test() personality ptr @__gxx_personality_sj0 {
 ; CHECK-NEXT:    pushq %r12
 ; CHECK-NEXT:    pushq %rbx
 ; CHECK-NEXT:    subq $104, %rsp
-; CHECK-NEXT:    movq $__gxx_personality_sj0, -104(%rbp)
+; CHECK-NEXT:    movq __gxx_personality_sj0@GOTPCREL(%rip), %rax
+; CHECK-NEXT:    movq %rax, -104(%rbp)
 ; CHECK-NEXT:    movq $GCC_except_table0, -96(%rbp)
 ; CHECK-NEXT:    movq %rbp, -88(%rbp)
 ; CHECK-NEXT:    movq %rsp, -72(%rbp)
@@ -28,7 +38,7 @@ define void @test() personality ptr @__gxx_personality_sj0 {
 ; CHECK-NEXT:    movl $1, -128(%rbp)
 ; CHECK-NEXT:  .Ltmp0:
 ; CHECK-NEXT:    movq %rcx, %rdi
-; CHECK-NEXT:    callq foo
+; CHECK-NEXT:    callq foo@PLT
 ; CHECK-NEXT:  .Ltmp1:
 ; CHECK-NEXT:    jmp .LBB0_2
 ; CHECK-NEXT:  .LBB0_3: # in Loop: Header=BB0_1 Depth=1