refactor: change LowerCtx::get_immediate to return a DataValue

This change abstracts away (from the perspective of the new backend) how immediate values are stored in InstructionData. It gathers large immediates from necessary places (e.g. constant pool) and delegates to `InstructionData::imm_value` for the rest. This refactor only touches original users of `LowerCtx::get_immediate` but a future change could do the same for any place the new backend is accessing InstructionData directly to retrieve immediates.

cranelift/codegen/src/isa/aarch64/lower.rs

@@ -10,7 +10,7 @@
 use crate::ir::condcodes::{FloatCC, IntCC};
 use crate::ir::types::*;
 use crate::ir::Inst as IRInst;
-use crate::ir::{InstructionData, Opcode, Type};
+use crate::ir::{Opcode, Type};
 use crate::machinst::lower::*;
 use crate::machinst::*;
 use crate::CodegenResult;
@@ -20,6 +20,7 @@ use crate::isa::aarch64::AArch64Backend;
 
 use super::lower_inst;
 
+use crate::data_value::DataValue;
 use log::{debug, trace};
 use regalloc::{Reg, RegClass, Writable};
 use smallvec::SmallVec;
@@ -126,22 +127,9 @@ pub(crate) fn const_param_to_u128<C: LowerCtx<I = Inst>>(
     ctx: &mut C,
     inst: IRInst,
 ) -> Option<u128> {
-    let data = match ctx.data(inst) {
-        &InstructionData::Shuffle { mask, .. } => ctx.get_immediate(mask),
-        &InstructionData::UnaryConst {
-            constant_handle, ..
-        } => ctx.get_constant_data(constant_handle),
-        _ => return None,
-    };
-    let data = data.clone().into_vec();
-
-    if data.len() == 16 {
-        let mut bytes = [0u8; 16];
-
-        bytes.copy_from_slice(&data);
-        Some(u128::from_le_bytes(bytes))
-    } else {
-        None
+    match ctx.get_immediate(inst) {
+        Some(DataValue::V128(bytes)) => Some(u128::from_le_bytes(bytes)),
+        _ => None,
     }
 }