| Issue |
168837
|
| Summary |
[MLIR] Invalid LLVM dialect generated after lowering
|
| Labels |
mlir
|
| Assignees |
|
| Reporter |
RJerrica
|
Hi, I used MLIR to lower a program to LLVM IR. However, the process generated an invalid LLVM dialect program that cannot be translated to LLVM IR. Here is the code example.
### Input Program
```llvm
// vector_add.mlir
module {
func.func @vector_add(%A: memref<100xf32>, %B: memref<100xf32>, %C: memref<100xf32>) {
%c0 = index.constant 0
%c1 = index.constant 1
%c100 = index.constant 100
%c256 = index.constant 256
gpu.launch blocks(%block_x, %block_y, %block_z) in (%grid_x = %c1, %grid_y = %c1, %grid_z = %c1)
threads(%thread_x, %thread_y, %thread_z) in (%block_size_x = %c256, %block_size_y = %c1, %block_size_z = %c1) {
%temp_global_id = index.mul %block_x, %block_size_x
%global_id = index.add %temp_global_id, %thread_x
%within_bounds = index.cmp slt(%global_id, %c100)
scf.if %within_bounds {
%a_val = memref.load %A[%global_id] : memref<100xf32>
%b_val = memref.load %B[%global_id] : memref<100xf32>
%sum = arith.addf %a_val, %b_val : f32
memref.store %sum, %C[%global_id] : memref<100xf32>
}
gpu.terminator
}
func.return
}
}
```
### MLIR Command
I used the following command to lower the program to the LLVM dialect and then to LLVM IR.
```bash
mlir-opt vector_add.mlir \
--convert-scf-to-cf \
--convert-gpu-to-nvvm \
--convert-cf-to-llvm \
--convert-index-to-llvm \
--convert-arith-to-llvm \
--convert-math-to-llvm \
--convert-func-to-llvm \
--finalize-memref-to-llvm \
-convert-nvvm-to-llvm \
--reconcile-unrealized-casts \
-o vector_add_llvm.mlir
```
Then, I use `mlir-translate` to convert the LLVM dialect module to LLVM IR. However, the generated LLVM dialect program is invalid because it contains numerous `unrealized_conversion_cast` operations, such as `%20 = builtin.unrealized_conversion_cast %19 : i64 to index` (See below for the logs).
```bash
mlir-translate --mlir-to-llvmir vector_add_llvm.mlir -o vector_add.ll
vector_add_llvm.mlir:6:10: error: LLVM Translation failed for operation: builtin.unrealized_conversion_cast
%3 = builtin.unrealized_conversion_cast %2 : i64 to index
^
vector_add_llvm.mlir:6:10: note: see current operation: %3 = "builtin.unrealized_conversion_cast"(%2) : (i64) -> index
```
### Version
```bash
mlir-opt --version
LLVM (http://llvm.org/):
LLVM version 22.0.0git
Optimized build with assertions.
```
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