[vulkan] Fix SPV physical ptr load alignment (#6139)

Issue: #6072
Ref #6136

### Brief Summary

We misread the specs, the `aligned` parameter takes a uint literal, not
a value. We used to feed in a value, but since SPIR-V wouldn't care, we
are actually feeding the value id as an alignment and probably causing
performance regression due to that.

taichi/codegen/spirv/spirv_ir_builder.cpp

@@ -1169,16 +1169,23 @@ Value IRBuilder::load_variable(Value pointer, const SType &res_type) {
             pointer.flag == ValueKind::kStructArrayPtr ||
             pointer.flag == ValueKind::kPhysicalPtr);
   Value ret = new_value(res_type, ValueKind::kNormal);
-  ib_.begin(spv::OpLoad).add_seq(res_type, ret, pointer).commit(&function_);
+  if (pointer.flag == ValueKind::kPhysicalPtr) {
+    uint32_t alignment = uint32_t(get_primitive_type_size(res_type.dt));
+    ib_.begin(spv::OpLoad)
+        .add_seq(res_type, ret, pointer, spv::MemoryAccessAlignedMask,
+                 alignment)
+        .commit(&function_);
+  } else {
+    ib_.begin(spv::OpLoad).add_seq(res_type, ret, pointer).commit(&function_);
+  }
   return ret;
 }
 void IRBuilder::store_variable(Value pointer, Value value) {
   TI_ASSERT(pointer.flag == ValueKind::kVariablePtr ||
             pointer.flag == ValueKind::kPhysicalPtr);
   TI_ASSERT(value.stype.id == pointer.stype.element_type_id);
   if (pointer.flag == ValueKind::kPhysicalPtr) {
-    Value alignment = uint_immediate_number(
-        t_uint32_, get_primitive_type_size(value.stype.dt));
+    uint32_t alignment = uint32_t(get_primitive_type_size(value.stype.dt));
     ib_.begin(spv::OpStore)
         .add_seq(pointer, value, spv::MemoryAccessAlignedMask, alignment)
         .commit(&function_);