| Issue |
117133
|
| Summary |
[indvars] Miscompile when loop body has an operation with Undefined Behaviour
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Nirhar
|
Here is the problematic IR:
```
define i32 @widget() {
bb:
br label %bb1
bb1: ; preds = %bb5, %bb
%phi = phi i32 [ 0, %bb ], [ %udiv6, %bb5 ]
%phi2 = phi i32 [ 1, %bb ], [ %add, %bb5 ]
%icmp = icmp eq i32 %phi, 0
br i1 %icmp, label %bb3, label %bb8
bb3: ; preds = %bb1
%udiv = udiv i32 10, %phi2
%urem = urem i32 %udiv, 10
%icmp4 = icmp eq i32 %urem, 0
br i1 %icmp4, label %bb7, label %bb5
bb5: ; preds = %bb3
%udiv6 = udiv i32 %phi2, 0
%add = add i32 %phi2, 1
br label %bb1
bb7: ; preds = %bb3
ret i32 5
bb8: ; preds = %bb1
ret i32 7
}
```
produces incorrect IR when `indvars` pass is run. I suspect this is because of the `%udiv6 = udiv i32 %phi2, 0` divide by zero operation.
Look at the indvars transformation here: https://godbolt.org/z/cz1r5178h
The original IR must return 5, while the transformed IR returns 7
Proof of wrong transformation: https://alive2.llvm.org/ce/z/vPFhzg
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