[SVE] Add codegen support for vscale_range() function attribute (#1…

…6962)

This commit adds support for the `vscale_range()` LLVM function attribute to be generated for SVE and SME targets.
Some LLVM optimisation passes make use of the `vscale_range()` function attribute when scalable vectors are present (e.g. BasicAA llvm/llvm-project/pull/80445), so we include it alongside the "target_cpu" and "target-features" attributes.

src/target/llvm/codegen_aarch64.cc

@@ -27,6 +27,7 @@
 #include <llvm/Target/TargetMachine.h>
 #include <tvm/runtime/registry.h>
 
+#include "../../arith/scalable_expression.h"
 #include "codegen_cpu.h"
 #include "llvm_instance.h"
 
@@ -40,6 +41,7 @@ class CodeGenAArch64 final : public CodeGenCPU {
 
   void VisitStmt_(const AttrStmtNode* op);
   void AddFunction(const GlobalVar& gvar, const PrimFunc& f);
+  void SetTargetAttributes(llvm::Function* func);
 
   bool func_has_pstate_sm = false;
   bool func_has_pstate_za = false;
@@ -51,6 +53,17 @@ void CodeGenAArch64::AddFunction(const GlobalVar& gvar, const PrimFunc& f) {
   CodeGenCPU::AddFunction(gvar, f);
 }
 
+void CodeGenAArch64::SetTargetAttributes(llvm::Function* func) {
+#if TVM_LLVM_VERSION >= 130
+  // Add vscale_range() function attribute when appropriate.
+  if (llvm_target_->TargetHasCPUFeature("sve") || llvm_target_->TargetHasCPUFeature("sme")) {
+    func->addFnAttr(llvm::Attribute::getWithVScaleRangeArgs(
+        *llvm_target_->GetContext(), 1, tvm::arith::kAArch64VScaleValues.size()));
+  }
+#endif
+  CodeGenCPU::SetTargetAttributes(func);
+}
+
 /*!
  * \brief Visit and handle AArch64 specific pragmas. To be AArch64 specific,
  * the expectation is that they are prepended with "pragma_aarch64".

src/target/llvm/codegen_llvm.h

@@ -431,7 +431,7 @@ class CodeGenLLVM : public ExprFunctor<llvm::Value*(const PrimExpr&)>,
    *
    * \param func The function to set attributes on.
    */
-  void SetTargetAttributes(llvm::Function* func);
+  virtual void SetTargetAttributes(llvm::Function* func);
   /*!
    * \brief Emit LLVM IR for conversion functions __extendhfsf2 and __truncsfhf2
    *        into the current llvm::Module.

tests/python/codegen/test_target_codegen_aarch64.py

@@ -537,6 +537,44 @@ def my_func(a: T.handle):
     assert re.findall(r" store <vscale x 4 x float>", llvm), "No scalable store in generated LLVM."
 
 
+@pytest.mark.skipif(
+    llvm_version_major() < 13,
+    reason="Function attribute vscale_range() is not supported in earlier versions of LLVM",
+)
+@pytest.mark.parametrize(
+    "mattr,expect_attr",
+    [
+        ("+neon", False),
+        ("+sve", True),
+        ("+v9a", True),
+        ("+sme", True),
+    ],
+)
+def test_vscale_range_function_attribute(mattr, expect_attr):
+    target = f"llvm -mtriple=aarch64-linux-gnu -mattr={mattr}"
+
+    m = te.var("m")
+    A = te.placeholder(m, dtype="float32", name="A")
+    C = te.compute((m), lambda i: A[i] + 1, name="C")
+    s = te.create_schedule([C.op])
+
+    with tvm.target.Target(target) as target:
+        f = tvm.build(s, [A, C], target)
+
+    # Check if the vscale_range() attribute exists
+    ll = f.get_source("ll")
+    attr = re.findall(rf".*vscale_range\(\d+,\d+\)*.", ll)
+
+    if expect_attr:
+        assert (
+            len(attr) > 0
+        ), f"Function attribute vscale_range() was not found in generated LLVM IR"
+    else:
+        assert (
+            len(attr) == 0
+        ), f"Unexpected function attribute vscale_range() was found in generated LLVM IR"
+
+
 @pytest.mark.skipif(
     llvm_version_major() < 16, reason="Test requires an LLVM version of at least 16 to target SME"
 )