| Issue |
83417
|
| Summary |
[SimplifyCFG] Missed optimization: simplify if-else BBs that share common destinations
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
XChy
|
Alive2 proof: https://alive2.llvm.org/ce/z/Q3dd5y
### Motivating example
```llvm
define void @src(i1 %c1, i1 %c2) {
entry:
br i1 %c1, label %then, label %else
then:
br i1 %c2, label %bb1, label %bb2
else:
br i1 %c2, label %bb2, label %bb1
bb1:
call void @dummy1()
ret void
bb2:
call void @dummy2()
ret void
}
```
can be folded to
```llvm
define void @tgt(i1 %c1, i1 %c2) {
entry:
%xor = xor i1 %c1, %c2
br i1 %xor, label %bb2, label %bb1
bb1:
call void @dummy1()
ret void
bb2:
call void @dummy2()
ret void
}
```
Here both `then` and `else` are trivial basicblocks with only a conditional branch inst, but I think it's possible to generalize it,
like replacing the condition of one of branch inst with `%c3`: https://alive2.llvm.org/ce/z/Xw9Ms2.
### Real-world motivation
This snippet of IR is derived from [z3/src/sat/tactic/goal2sat.cpp@convert_iff](https://github.com/Z3Prover/z3/blob/2880ea39719971226e616d1077788288d6107632/src/sat/tactic/goal2sat.cpp#L626) (after O3 pipeline).
The example above is a reduced version. Original IR comes from https://github.com/dtcxzyw/llvm-opt-benchmark/blob/main/bench/z3/original/goal2sat.cpp.ll, if you want optimal one, please email me please.
**Let me know if you can confirm that it's an optimization opportunity, thanks.**
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