[lang] Migrate TensorType expansion for svd from Python code to Front…

…end IR (#6972)

Issue: #5819

### Brief Summary

python/taichi/_funcs.py

@@ -162,7 +162,6 @@ def _svd3d(A, dt, iters=None):
         Decomposed 3x3 matrices `U`, 'S' and `V`.
     """
     assert A.n == 3 and A.m == 3
-    inputs = get_runtime().prog.current_ast_builder().expand_expr([A.ptr])
     assert dt in [f32, f64]
     if iters is None:
         if dt == f32:
@@ -171,10 +170,10 @@ def _svd3d(A, dt, iters=None):
             iters = 8
     if dt == f32:
         rets = get_runtime().prog.current_ast_builder().sifakis_svd_f32(
-            *inputs, iters)
+            A.ptr, iters)
     else:
         rets = get_runtime().prog.current_ast_builder().sifakis_svd_f64(
-            *inputs, iters)
+            A.ptr, iters)
     assert len(rets) == 21
     U_entries = rets[:9]
     V_entries = rets[9:18]

taichi/math/svd.h

@@ -42,17 +42,20 @@ std::tuple<Expr,
            Expr,
            Expr,
            Expr>
-sifakis_svd_export(ASTBuilder *ast_builder,
-                   const Expr &a00,
-                   const Expr &a01,
-                   const Expr &a02,
-                   const Expr &a10,
-                   const Expr &a11,
-                   const Expr &a12,
-                   const Expr &a20,
-                   const Expr &a21,
-                   const Expr &a22,
-                   int num_iters) {
+sifakis_svd_export(ASTBuilder *ast_builder, const Expr &mat, int num_iters) {
+  auto expanded_exprs = ast_builder->expand_expr({mat});
+  TI_ASSERT(expanded_exprs.size() == 9);
+
+  Expr a00 = expanded_exprs[0];
+  Expr a01 = expanded_exprs[1];
+  Expr a02 = expanded_exprs[2];
+  Expr a10 = expanded_exprs[3];
+  Expr a11 = expanded_exprs[4];
+  Expr a12 = expanded_exprs[5];
+  Expr a20 = expanded_exprs[6];
+  Expr a21 = expanded_exprs[7];
+  Expr a22 = expanded_exprs[8];
+
   static_assert(sizeof(Tf) == sizeof(Ti), "");
   constexpr Tf Four_Gamma_Squared = 5.82842712474619f;
   constexpr Tf Sine_Pi_Over_Eight = 0.3826834323650897f;