[SVE] Add vscale builtin

Add a vscale builtin and lowering to `llvm.vscale`. This will be used in
subsequent patches for expressing scalable vectors in TIR.

Co-authored-by: Luke Hutton <luke.hutton@arm.com>
Co-authored-by: Neil Hickey <neil.hickey@arm.com>

include/tvm/tir/builtin.h

@@ -909,6 +909,11 @@ TVM_DLL const Op& anylist_setitem_call_packed();
  */
 TVM_DLL const Op& anylist_setitem_call_cpacked();
 
+/*!
+ * \brief Get the target's vscale value
+ */
+TVM_DLL const Op& vscale();
+
 /*! \brief The kind of structure field info used in intrinsic */
 enum TVMStructFieldKind : int {
   // array head address

python/tvm/script/ir_builder/tir/ir.py

@@ -1862,6 +1862,7 @@ def wrapped(*args, **kwargs):
 anylist_resetitem = _op_wrapper(_tir_op.anylist_resetitem)
 anylist_setitem_call_packed = _op_wrapper(_tir_op.anylist_setitem_call_packed)
 anylist_setitem_call_cpacked = _op_wrapper(_tir_op.anylist_setitem_call_cpacked)
+vscale = _op_wrapper(_tir_op.vscale)
 
 
 def _dtype_forward(func):
@@ -2199,4 +2200,5 @@ def wrapped(*args, **kwargs):
     "IterVar",
     "CommReducer",
     "Range",
+    "vscale",
 ]

python/tvm/tir/__init__.py

@@ -88,6 +88,7 @@
 from .op import q_multiply_shift, q_multiply_shift_per_axis, shift_left, shift_right
 from .op import TVMBackendAllocWorkspace, TVMBackendFreeWorkspace
 from .op import start_profile_intrinsic, end_profile_intrinsic
+from .op import vscale
 from .generic import add, subtract, multiply
 
 from .schedule import StmtSRef, BlockScope, ScheduleState, Schedule, ScheduleError

python/tvm/tir/op.py

@@ -3338,6 +3338,16 @@ def anylist_setitem_call_cpacked(list_handle, index, func_name, *args):
     )
 
 
+def vscale():
+    """Get the target's vscale value
+    Returns
+    -------
+    call : PrimExpr
+        Call to the vscale intrinsic
+    """
+    return call_intrin("int32", "tir.vscale")
+
+
 # pylint: disable=unnecessary-lambda
 sum = comm_reducer(lambda x, y: x + y, lambda t: const(0, dtype=t), name="sum")
 min = comm_reducer(lambda x, y: _ffi_api._OpMin(x, y, None), max_value, name="min")  # type: ignore

src/target/llvm/codegen_llvm.cc

@@ -1478,6 +1478,12 @@ llvm::Value* CodeGenLLVM::CreateIntrinsic(const CallNode* op) {
     return builder_->CreateAssumption(cond);
   } else if (op->op.same_as(builtin::tvm_thread_invariant())) {
     return MakeValue(op->args[0]);
+#if TVM_LLVM_VERSION >= 110
+  } else if (op->op.same_as(builtin::vscale())) {
+    llvm::Intrinsic::ID id = llvm::Intrinsic::vscale;
+    llvm::Function* f = GetIntrinsicDecl(id, builder_->getInt32Ty(), {});
+    return builder_->CreateCall(f);
+#endif
   } else {
     LOG(FATAL) << "unknown intrinsic " << op->op;
   }

src/tir/op/builtin.cc

@@ -394,6 +394,9 @@ TIR_DEFINE_BUILTIN_FUNC(anylist_setitem_call_packed)
 
 TIR_DEFINE_BUILTIN_FUNC(anylist_setitem_call_cpacked)
     .set_attr<TCallEffectKind>("TCallEffectKind", Integer(CallEffectKind::kOpaque));
+
+TIR_DEFINE_BUILTIN_FUNC(vscale).set_attr<TCallEffectKind>("TCallEffectKind",
+                                                          Integer(CallEffectKind::kOpaque));
 }  // namespace builtin
 }  // namespace tir
 }  // namespace tvm

tests/python/codegen/test_target_codegen_aarch64.py

@@ -16,10 +16,8 @@
 # under the License.
 import tvm
 from tvm import te
-from tvm.script import tir as TIR
+from tvm.script import tir as T
 import re
-import os
-import ctypes
 import pytest
 
 from tvm.target.codegen import llvm_version_major
@@ -476,5 +474,23 @@ def check_correct_assembly(type):
     check_correct_assembly(type=dtype)
 
 
+@pytest.mark.skipif(
+    llvm_version_major() < 10, reason="Vscale is not supported in earlier versions of LLVM"
+)
+def test_codegen_vscale():
+    target = "llvm -mtriple=aarch64-linux-gnu -mattr=+sve"
+    vscale = tvm.tir.vscale()
+
+    @T.prim_func
+    def main(A: T.Buffer((5,), "int32")):
+        for i in range(5):
+            A[i] = 2 * vscale
+
+    build_mod = tvm.build(main, target=target)
+    llvm = build_mod.get_source()
+
+    assert re.findall(r"llvm.vscale.i32", llvm), "No vscale in generated LLVM."
+
+
 if __name__ == "__main__":
     tvm.testing.main()