[CodeGen] Do not emit TRAP for `unreachable` after `@llvm.trap` (#94570)

With `--trap-unreachable`, `clang` can emit double `TRAP` instructions
for code that contains a call to `__builtin_trap()`:

```
> cat test.c
void test() { __builtin_trap(); }
> clang test.c --target=x86_64 -mllvm --trap-unreachable -O1 -S -o -
...
test:
...
  ud2
  ud2
...
```

`SimplifyCFGPass` inserts `unreachable` after a call to a `noreturn`
function, and later this instruction causes `TRAP/G_TRAP` to be emitted
in `SelectionDAGBuilder::visitUnreachable()` or
`IRTranslator::translateUnreachable()` if
`TargetOptions.TrapUnreachable` is set.

The patch checks the instruction before `unreachable` and avoids
inserting an additional trap.

0 files changed, 0 insertions, 0 deletions