sepcnt opened a new issue, #20343:
URL: https://github.com/apache/tvm/issues/20343
### Expected behavior
Block access-region analysis should handle valid `uint32`/`uint64`
conditions without crashing. If an unsigned predicate cannot be solved,
conservatively including both branches is sufficient.
### Actual behavior
Analyzing `if_then_else(mask != 0, data[0], data[3])` with an unsigned
`mask` raises:
```text
tvm.error.InternalError: cannot make uint from negative value -1
```
There is **no negative constant in the input program**, and all buffer
accesses are in bounds. Both `uint32` and `uint64` reproduce; the `int32`
control passes. An explicit `mask == 0` condition also reproduces.
The failure occurs when analyzing the implicit else condition, `mask == 0`.
`ConditionalBoundsContext::TrySolveCondition` accepts unsigned variables and
passes the condition to `SolveInequalitiesToRange` / `SolveLinearInequalities`.
The solver constructs signed mathematical coefficients using the program
variable's unsigned type, for example:
```cpp
PrimExpr c_pos = MakeConst(v_ty, neg.first / first_gcd);
```
This attempts to represent an internally generated `-1` as an unsigned
constant. The issue is a mismatch between conditional-analysis eligibility and
the inequality solver's supported arithmetic domain, not an invalid user
literal.
### Environment
- Apache TVM `main`, commit `cc0f9f07c17c8118a781fdca55f7fe45f7de916a`
(0.26.dev0).
- Windows, Python 3.12.13, locally built TVM compiler/runtime DLLs.
- Reproduced directly in Apache TVM, without TileLang. No GPU execution or
LLVM code generation is required.
### Steps to reproduce
Run this script against the above revision:
```python
from tvm import s_tir, tirx
mask_buffer = tirx.decl_buffer((1,), "uint32", name="mask_buffer")
data = tirx.decl_buffer((4,), "int32", name="data")
output = tirx.decl_buffer((1,), "int32", name="output")
mask = tirx.Var("mask", "uint32")
body = tirx.SeqStmt([
tirx.Bind(mask, mask_buffer[0]),
tirx.BufferStore(
output, tirx.if_then_else(mask != 0, data[0], data[3]), [0]
),
])
block = tirx.SBlock([], [], [], "conditional_read", body)
buffers = {buf: buf for buf in (mask_buffer, data, output)}
print(s_tir.analysis.get_sblock_access_region(block, buffers))
```
Replace both `uint32` occurrences with `uint64` to reproduce the same error,
or with `int32` for the passing control. The expected conservative read region
for `data` is `[0:4]`.
### Triage
* needs-triage
* type: bug
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