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whisper.cpp
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metal : implement rope_back operator (llama/24725) 

Reuse existing rope kernels with a function constant to toggle forward/backward
rotation, avoiding duplicate kernel code.

Assisted-by: pi:llama.cpp/Qwen3.6-27B
This commit is contained in:
Georgi Gerganov 2026-06-17 20:36:05 +03:00
parent ad19c98240
commit d911569230
4 changed files with 11 additions and 2 deletions
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7
ggml/src/ggml-metal/ggml-metal-device.cpp
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@ -1703,7 +1703,9 @@ ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_norm(ggml_metal_
}
ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_rope(ggml_metal_library_t lib, const ggml_tensor * op) {
assert(op->op == GGML_OP_ROPE);
assert(op->op == GGML_OP_ROPE || op->op == GGML_OP_ROPE_BACK);
const bool is_back = op->op == GGML_OP_ROPE_BACK;
char base[256];
char name[256];
@ -1727,13 +1729,14 @@ ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_rope(ggml_metal_
snprintf(base, 256, "kernel_rope_norm_%s", ggml_type_name(op->src[0]->type));
}
snprintf(name, 256, "%s_imrope=%d", base, is_imrope ? 1 : 0);
snprintf(name, 256, "%s_imrope=%d_is_back=%d", base, is_imrope ? 1 : 0, is_back ? 1 : 0);
ggml_metal_pipeline_with_params res = ggml_metal_library_get_pipeline(lib, name);
if (!res.pipeline) {
ggml_metal_cv_t cv = ggml_metal_cv_init();
ggml_metal_cv_set_bool(cv, is_imrope, FC_ROPE + 0);
ggml_metal_cv_set_bool(cv, is_back, FC_ROPE + 1);
res = ggml_metal_library_compile_pipeline(lib, base, name, cv);

1
ggml/src/ggml-metal/ggml-metal-device.m
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@ -1184,6 +1184,7 @@ bool ggml_metal_device_supports_op(ggml_metal_device_t dev, const struct ggml_te
case GGML_OP_RMS_NORM:
return has_simdgroup_reduction && (ggml_is_contiguous_rows(op->src[0]));
case GGML_OP_ROPE:
case GGML_OP_ROPE_BACK:
return true;
case GGML_OP_IM2COL:
return ggml_is_contiguous(op->src[1]) && op->src[1]->type == GGML_TYPE_F32 && (op->type == GGML_TYPE_F16 || op->type == GGML_TYPE_F32);

1
ggml/src/ggml-metal/ggml-metal-ops.cpp
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@ -375,6 +375,7 @@ static int ggml_metal_op_encode_impl(ggml_metal_op_t ctx, int idx) {
n_fuse = ggml_metal_op_norm(ctx, idx);
} break;
case GGML_OP_ROPE:
case GGML_OP_ROPE_BACK:
{
n_fuse = ggml_metal_op_rope(ctx, idx);
} break;

4
ggml/src/ggml-metal/ggml-metal.metal
View File

@ -4358,6 +4358,7 @@ template [[host_name("kernel_mul_mv_bf16_bf16_short")]] kernel mul_mv_t_t_short_
#endif
constant bool FC_rope_is_imrope [[function_constant(FC_ROPE + 0)]];
constant bool FC_rope_is_back [[function_constant(FC_ROPE + 1)]];
static float rope_yarn_ramp(const float low, const float high, const int i0) {
const float y = (i0 / 2 - low) / max(0.001f, high - low);
@ -4381,6 +4382,9 @@ static void rope_yarn(
}
*cos_theta = cos(theta) * mscale;
*sin_theta = sin(theta) * mscale;
if (FC_rope_is_back) {
*sin_theta *= -1.0f;
}
}
// Apparently solving `n_rot = 2pi * x * base^((2 * max_pos_emb) / n_dims)` for x, we get