[P0] Codegen pass mishandles promoted func args (neura.constant {value="%arg*"}) #154
Description
Summary
When function arguments are promoted to constants (via --promote-func-arg-to-const), the IR contains neura.constant ops whose value is a string like "%arg0". The current codegen incorrectly treats these as numeric immediates (e.g., #2) and/or yields an empty src in the generated YAML, causing downstream consumers to “not recognize” the operand.
Expected: codegen should preserve %arg* as symbolic operands and respect their mapping info.
Actual: %arg* is collapsed to a numeric immediate or results in an empty src.
Problem Description
When writing the FFT kernel like this:
void fft_cgra_kernel(float *data, const float *tw, long long N);
Compile/transform with the pass pipeline that includes --promote-func-arg-to-const.
Observe IR (example):
%0 = "neura.constant"() <{value = "%arg0"}> {mapping_locs = [{id = 2 : i32, resource = "tile", time_step = 12 : i32, x = 2 : i32, y = 0 : i32}]} : () -> !neura.data<!llvm.ptr, i1>
%1 = "neura.constant"() <{value = "%arg1"}> {mapping_locs = [{id = 14 : i32, resource = "tile", time_step = 12 : i32, x = 2 : i32, y = 3 : i32}]} : () -> !neura.data<!llvm.ptr, i1>
%2 = "neura.constant"() <{value = "%arg2"}> {mapping_locs = [{id = 10 : i32, resource = "tile", time_step = 12 : i32, x = 2 : i32, y = 2 : i32}]} : () -> !neura.data<i64, i1>
Run the codegen pass.
Inspect the emitted ASM/YAML: %arg* is turned into an immediate like #2 or the YAML has an empty src operand. (Fixed)
Current Solution
We currently directly output %arg* for both YAML and ASM files like this:
YAML
- opcode: "CONSTANT"
src_operands:
- operand: "%arg1"
color: "RED"
dst_operands:
- operand: "NORTH"
color: "RED"
ASM
PE(3,1):
{
CONSTANT, [%arg1, RED] -> [NORTH, RED]
} (t=3)
However, when implementing this in the simulator, we might need to further discuss this issue.