| Issue |
120539
|
| Summary |
[SimplifyCFG] Convert conditional branch into unconditional branch if the incoming values of phi node can be represented by the condition
|
| Labels |
missed-optimization,
llvm:transforms
|
| Assignees |
dtcxzyw
|
| Reporter |
dtcxzyw
|
Alive2: https://alive2.llvm.org/ce/z/K8WVKU
```
define i1 @src1(i32 noundef %0, i32 noundef %1) {
start:
%2 = icmp eq i32 %0, 0
br i1 %2, label %bb6, label %bb5
bb6:
%3 = icmp eq i32 %1, 0
br i1 %3, label %bb2, label %bb3
bb5:
%.not = icmp ult i32 %0, %1
br i1 %.not, label %bb3, label %bb2
bb2:
br label %bb3
bb3:
%_0.sroa.0.0 = phi i1 [ true, %bb2 ], [ false, %bb6 ], [ false, %bb5 ]
ret i1 %_0.sroa.0.0
}
define i1 @tgt1(i32 %0, i32 %1) {
start:
%2 = icmp eq i32 %0, 0
%3 = icmp eq i32 %1, 0
%.not = icmp uge i32 %0, %1
%cond = select i1 %2, i1 %3, i1 %.not
ret i1 %cond
}
```
We can convert conditional branches into unconditional branches and adjust incoming values of the phi node:
```
define i1 @src2(i32 noundef %0, i32 noundef %1) {
start:
%2 = icmp eq i32 %0, 0
br i1 %2, label %bb6, label %bb5
bb6:
%3 = icmp eq i32 %1, 0
br i1 %3, label %bb2, label %bb3
bb5:
%.not = icmp ult i32 %0, %1
br i1 %.not, label %bb3, label %bb2
bb2:
br label %bb3
bb3:
%_0.sroa.0.0 = phi i1 [ true, %bb2 ], [ false, %bb6 ], [ false, %bb5 ]
ret i1 %_0.sroa.0.0
}
define i1 @tgt2(i32 noundef %0, i32 noundef %1) {
start:
%2 = icmp eq i32 %0, 0
br i1 %2, label %bb6, label %bb5
bb6:
%3 = icmp eq i32 %1, 0
br i1 %3, label %bb2, label %bb3
bb5:
%.not = icmp uge i32 %0, %1
br label %bb3
bb2:
br label %bb3
bb3:
%_0.sroa.0.0 = phi i1 [ true, %bb2 ], [ false, %bb6 ], [ %.not, %bb5 ]
ret i1 %_0.sroa.0.0
}
```
Finally we will get a select instruction with `foldTwoEntryPHINode`.
Inspired by https://github.com/llvm/llvm-project/pull/120177: https://rust.godbolt.org/z/cEjsW56Pq
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