[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
diff --git a/test/ScopDetect/callbr.ll b/test/ScopDetect/callbr.ll
index 1981f01..f226818 100644
--- a/test/ScopDetect/callbr.ll
+++ b/test/ScopDetect/callbr.ll
@@ -12,7 +12,7 @@
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:
