[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

1 files changed, 1 insertions, 1 deletions

diff --git a/polly/test/ScopDetect/callbr.ll b/polly/test/ScopDetect/callbr.ll
index 1981f0127e87..f226818a4ca1 100644
--- a/polly/test/ScopDetect/callbr.ll
+++ b/polly/test/ScopDetect/callbr.ll
@@ -12,7 +12,7 @@ target triple = "x86_64-unknown-linux-gnu"
 
 define void @func(i32 %n, double* noalias nonnull %A) {
 entry:
-  callbr void asm sideeffect "", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@func, %for)) #1
+  callbr void asm sideeffect "", "!i,~{dirflag},~{fpsr},~{flags}"() #1
           to label %fallthrough [label %for]
 
 fallthrough: