Raise error when AIR_TRANSFORM_TILING_SCRIPT file is not found

[erwei-xilinx]

Summary

• When AIR_TRANSFORM_TILING_SCRIPT is set to a relative path and the script is run from a directory that doesn't contain that file, the driver now raises a clear FileNotFoundError instead of silently falling back to a default transform IR that causes an opaque MLIRError: Failure while executing pass pipeline in aircc.

Root cause

_get_transform_ir_string() in driver.py caught FileNotFoundError and fell back to a hardcoded default transform IR. This default IR only does simple 32x32 tiling without creating air.herd ops or proper memory staging, so the downstream aircc pass pipeline fails. The warning message (Warning: Custom tiling script file not found) was printed after the traceback, making it easy to miss.

Reproduced by running matmul.py from a directory other than examples/matmul/ with AIR_TRANSFORM_TILING_SCRIPT=transform_aie2.mlir (relative path). The new error message is:

FileNotFoundError: AIR_TRANSFORM_TILING_SCRIPT is set to 'transform_aie2.mlir'
but the file was not found (cwd: /tmp).
Use an absolute path or run from the directory containing the script.

Test plan

• Set AIR_TRANSFORM_TILING_SCRIPT=transform_aie2.mlir and run matmul from a wrong directory — should get clear FileNotFoundError
• Run matmul from examples/matmul/ with the env var set — should work as before
• Run without AIR_TRANSFORM_TILING_SCRIPT set — default fallback still works

🤖 Generated with Claude Code