Add benchmark for JITgen (#2260)

Adds the benchmark I used for measuring the witness generation JIT in
#2242.

pipeline/Cargo.toml

@@ -62,6 +62,10 @@ walkdir = "2.4.0"
 name = "evaluator_benchmark"
 harness = false
 
+[[bench]]
+name = "jit_witgen_benchmark"
+harness = false
+
 [lints]
 workspace = true
 

pipeline/benches/jit_witgen_benchmark.rs

@@ -0,0 +1,25 @@
+use ::powdr_pipeline::Pipeline;
+use powdr_number::GoldilocksField;
+
+use criterion::{criterion_group, criterion_main, Criterion};
+
+type T = GoldilocksField;
+
+fn jit_witgen_benchmark(c: &mut Criterion) {
+    let mut group = c.benchmark_group("jit-witgen-benchmark");
+    group.sample_size(10);
+
+    // Poseidon benchmark
+    let mut pipeline =
+        Pipeline::<T>::default().from_file("../test_data/std/poseidon_benchmark.asm".into());
+    pipeline.compute_optimized_pil().unwrap();
+    pipeline.compute_fixed_cols().unwrap();
+
+    group.bench_function("jit_witgen_benchmark", |b| {
+        b.iter(|| pipeline.clone().compute_witness().unwrap())
+    });
+    group.finish();
+}
+
+criterion_group!(benches_jit_witgen, jit_witgen_benchmark);
+criterion_main!(benches_jit_witgen);

test_data/std/poseidon_benchmark.asm

@@ -0,0 +1,33 @@
+use std::machines::hash::poseidon_gl::PoseidonGL;
+
+// 2^17 rows -> ~2^16 Poseidon hashes
+machine Main with degree: 131072 {
+    reg pc[@pc];
+    reg X0[<=];
+    reg X1[<=];
+    reg X2[<=];
+    reg X3[<=];
+    reg X4[<=];
+    reg A;
+    reg B;
+    reg C;
+    reg D;
+
+    // 2^16 Poseidon hashes -> 2^21 rows in Poseidon machine
+    PoseidonGL poseidon(2097152, 2097152);
+
+    instr jmp l: label { pc' = l }
+
+    // Hash some constants (except the first element, to trick the loop detection)
+    instr poseidon X4 -> X0, X1, X2, X3
+        link ~> (X0, X1, X2, X3) = poseidon.poseidon_permutation(X4, 235763497586, 9827635653498, 112870, 289273673480943876, 230295874986745876, 6254867324987, 2087, 0, 0, 0, 0);
+
+    function main {
+
+        loop:
+        A, B, C, D <== poseidon(A);
+        jmp loop;
+
+        return;
+    }
+}