| Issue |
95919
|
| Summary |
[SimplifyCFG] `ForwardSwitchConditionToPHI` missed some cases
|
| Labels |
llvm:optimizations,
missed-optimization
|
| Assignees |
DianQK
|
| Reporter |
DianQK
|
I tried this IR:
```llvm
define { i64, i64 } @src(i64 noundef %arg, i64 noundef %arg1) local_unnamed_addr #0 {
bb:
switch i64 %arg1, label %bb7 [
i64 0, label %bb3
i64 1, label %bb2
]
bb2: ; preds = %bb
br label %bb3
bb7: ; preds = %bb
%i8 = udiv i64 %arg, %arg1
%i13 = shl nuw i64 %i8, 1
br label %bb3
bb3: ; preds = %bb7, %bb2, %bb
%i = phi i64 [ %i13, %bb7 ], [ %arg, %bb2 ], [ undef, %bb ]
%i4 = phi i64 [ 1, %bb7 ], [ 1, %bb2 ], [ %arg1, %bb ]
%i5 = insertvalue { i64, i64 } poison, i64 %i4, 0
%i6 = insertvalue { i64, i64 } %i5, i64 %i, 1
ret { i64, i64 } %i6
}
```
We can replace `[ 1, %bb2 ]` with `[ %arg1, %bb2 ]`. Then the final IR will become to:
```llvm
define { i64, i64 } @tgt(i64 noundef %arg, i64 noundef %arg1) {
bb:
%switch = icmp ult i64 %arg1, 2
br i1 %switch, label %bb3, label %bb7
bb7: ; preds = %bb
%i8 = udiv i64 %arg, %arg1
%i13 = shl nuw i64 %i8, 1
br label %bb3
bb3: ; preds = %bb, %bb7
%i = phi i64 [ %i13, %bb7 ], [ %arg, %bb ]
%i4 = phi i64 [ 1, %bb7 ], [ %arg1, %bb ]
%i5 = insertvalue { i64, i64 } poison, i64 %i4, 0
%i6 = insertvalue { i64, i64 } %i5, i64 %i, 1
ret { i64, i64 } %i6
}
```
Alive2: https://alive2.llvm.org/ce/z/HvwxHB.
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