Yingwei Zheng
287294d54d
[ConstraintElim] Do not allow overflows in Decomposition (#140541)
Consider the following case:
```
define i1 @pr140481(i32 %x) {
%cond = icmp slt i32 %x, 0
call void @llvm.assume(i1 %cond)
%add = add nsw i32 %x, 5001000
%mul1 = mul nsw i32 %add, -5001000
%mul2 = mul nsw i32 %mul1, 5001000
%cmp2 = icmp sgt i32 %mul2, 0
ret i1 %cmp2
}
```
Before this patch, `decompose(%mul2)` returns `-25010001000000 * %x +
4052193514966861312`.
Therefore, `%cmp2` will be simplified into true because `%x s< 0 &&
-25010001000000 * %x + 4052193514966861312 s<= 0` is unsat.
It is incorrect since the offset `-25010001000000 * 5001000 ->
4052193514966861312` signed wraps.
This patch treats a decomposition as invalid if overflows occur when
computing coefficients.
Closes https://github.com/llvm/llvm-project/issues/140481.
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