[Metal] Rewrite rules: Remove MetalSyncToCPU between Const and CPU Operator

metal/src/ops/sync.rs

@@ -1,8 +1,8 @@
 use crate::fact::MetalTypedFactExt;
 pub use crate::kernels::BinOps;
-use crate::tensor::MetalTensorExt;
 use crate::ops::MetalEvalOp;
-use crate::{ MetalFact, IntoMetal, MetalContext };
+use crate::tensor::MetalTensorExt;
+use crate::{IntoMetal, MetalContext, MetalFact};
 use derive_new::new;
 use std::fmt;
 use tract_core::internal::*;

metal/src/rewrite_rules/mod.rs

@@ -12,7 +12,7 @@ use tract_core::ops::konst::Const;
 pub use apply_rope::{as_apply_rope_rule, BasicApplyRope};
 pub use fuse_axis_op::fuse_axis_op;
 pub use new_gelu::{as_new_gelu_rule, BasicNewGelu};
-pub use rewire_metal_sync::rewire_metal_sync;
+pub use rewire_metal_sync::{rewire_metal_sync, rewire_metal_sync_after_const};
 pub use rms_norm::{as_rms_norm_rule, remove_rms_norm_cast, BasicRmsNorm};
 pub use rotate_half::{as_rotate_half_rule, BasicRotateHalf};
 pub use silu::{as_silu_rule, BasicSilu};

metal/src/rewrite_rules/rewire_metal_sync.rs

@@ -1,7 +1,9 @@
 use crate::ops::{MetalSync, MetalSyncKind};
-use crate::rewrite_rules::previous_node;
+use crate::rewrite_rules::{next_node, previous_node};
 use crate::rule_ensure;
+use crate::tensor::MetalTensorExt;
 use tract_core::internal::*;
+use tract_core::ops::konst::Const;
 
 pub fn rewire_metal_sync(
     _ctx: &(),
@@ -25,3 +27,26 @@ pub fn rewire_metal_sync(
         })?;
     Ok(Some(patch))
 }
+
+pub fn rewire_metal_sync_after_const(
+    _ctx: &(),
+    model: &TypedModel,
+    node: &TypedNode,
+    node_name: &str,
+    op: &Const,
+) -> TractResult<Option<TypedModelPatch>> {
+    // Search pattern => Const => ToCPU
+
+    let Some(gpu_const) = op.0.as_metal_tensor() else { return Ok(None) };
+    let cpu_const = gpu_const.to_cpu()?;
+
+    // Identify successor ToCpu
+    let Some(sync_cpu) = next_node(model, node) else { return Ok(None) };
+    let Some(sync_cpu_op) = sync_cpu.op_as::<MetalSync>() else { return Ok(None) };
+    rule_ensure!(sync_cpu_op.kind == MetalSyncKind::ToCpu);
+
+    let mut patch = TypedModelPatch::default();
+    let out = patch.wire_node(node_name.to_string(), Const(cpu_const.into(), None), &[])?;
+    patch.shunt_outside(model, sync_cpu.id.into(), out[0])?;
+    Ok(Some(patch))
+}

metal/src/transform.rs

@@ -7,8 +7,8 @@ use crate::ops::{self, MetalAxisOp, MetalSync, MetalSyncKind};
 #[allow(unused_imports)]
 use crate::rewrite_rules::{
     as_apply_rope_rule, as_new_gelu_rule, as_rms_norm_rule, as_rotate_half_rule, as_silu_rule,
-    fuse_axis_op, remove_rms_norm_cast, rewire_metal_sync, BasicApplyRope, BasicNewGelu,
-    BasicRmsNorm, BasicRotateHalf, BasicSilu,
+    fuse_axis_op, remove_rms_norm_cast, rewire_metal_sync, rewire_metal_sync_after_const,
+    BasicApplyRope, BasicNewGelu, BasicRmsNorm, BasicRotateHalf, BasicSilu,
 };
 use crate::tensor::MetalTensorExt;
 use crate::{IntoMetal, MetalFact, MetalTensor};
@@ -70,6 +70,7 @@ impl ModelTransform for MetalTransform {
 
         Rewriter::default()
             .with_rule_for::<MetalSync>("rewire-metal-sync", rewire_metal_sync)
+            .with_rule_for::<Const>("rewire-metal-sync-after-const", rewire_metal_sync_after_const)
             .with_rule_for::<MetalAxisOp>("fuse_axis_op", fuse_axis_op)
             .rewrite(&(), &mut new)?;
         *model = new;
@@ -365,7 +366,6 @@ fn convert_const(op: &Const) -> TractResult<Option<Const>> {
     Ok(Some(Const::new_with_opaque_fact(metal_const, Box::new(metal_fact))))
 }
 
-
 fn convert_element_wise_ops_to_metal(op: &ElementWiseOp) -> Option<ops::MetalElementWiseOp> {
     map_element_wise_ops!([
         (tract_core::ops::math::Abs, Abs),