tree 82438dcf4c1c28fe537bf8b0c2f0a4f4a936174f
parent 467fba1fc44ca017e66f0b1e535f9c7ed277c136
author Nikita Popov <npopov@redhat.com> 1657189663 +0200
committer Copybara-Service <copybara-worker@google.com> 1657873489 -0700

[IR] Don't use blockaddresses as callbr arguments

Following some recent discussions, this changes the representation
of callbrs in IR. The current blockaddress arguments are replaced
with `!` label constraints that refer directly to callbr indirect
destinations:

    ; Before:
    %res = callbr i8* asm "", "=r,r,i"(i8* %x, i8* blockaddress(@test8, %foo))
    to label %asm.fallthrough [label %foo]
    ; After:
    %res = callbr i8* asm "", "=r,r,!i"(i8* %x)
    to label %asm.fallthrough [label %foo]

The benefit of this is that we can easily update the successors of
a callbr, without having to worry about also updating blockaddress
references. This should allow us to remove some limitations:

* Allow unrolling/peeling/rotation of callbr, or any other
  clone-based optimizations
  (https://github.com/llvm/llvm-project/issues/41834)
* Allow duplicate successors
  (https://github.com/llvm/llvm-project/issues/45248)

This is just the IR representation change though, I will follow up
with patches to remove limtations in various transformation passes
that are no longer needed.

Differential Revision: https://reviews.llvm.org/D129288

GitOrigin-RevId: 2a721374aef326d4668f750d341c86d1aa1a0309