Port vconst to ISLE (AArch64) (#4750)

* Port `vconst` to ISLE (AArch64)

Ported the existing implementation of `vconst` to ISLE for AArch64, and
added support for 64-bit vector constants.

Also introduced 64-bit `vconst` support to the interpreter.

Copyright (c) 2022 Arm Limited

* Replace if-chains with match statements

Copyright (c) 2022 Arm Limited

Author: Damian Heaton

cranelift/codegen/src/isa/aarch64/inst.isle

@@ -2435,6 +2435,11 @@
       (if-let addr_reg (amode_is_reg addr))
       addr_reg)
 
+;; Lower a constant f64.
+(decl constant_f64 (u64) Reg)
+;; TODO: Port lower_constant_f64() to ISLE.
+(extern constructor constant_f64 constant_f64)
+
 ;; Lower a constant f128.
 (decl constant_f128 (u128) Reg)
 ;; TODO: Port lower_constant_f128() to ISLE.

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

@@ -1628,6 +1628,15 @@
 (rule (lower (resumable_trap trap_code))
       (side_effect (udf trap_code)))
 
+;;;; Rules for `vconst` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(rule (lower (has_type (ty_vec128 _) (vconst (u128_from_constant x))))
+      (constant_f128 x))
+
+(rule (lower (has_type ty (vconst (u64_from_constant x))))
+      (if (ty_vec64 ty))
+      (constant_f64 x))
+
 ;;;; Rules for `splat` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (rule (lower (has_type ty (splat x @ (value_type in_ty))))

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

@@ -8,7 +8,6 @@
 //! - Floating-point immediates (FIMM instruction).
 
 use super::lower_inst;
-use crate::data_value::DataValue;
 use crate::ir::condcodes::{FloatCC, IntCC};
 use crate::ir::types::*;
 use crate::ir::Inst as IRInst;
@@ -94,13 +93,6 @@ pub(crate) fn input_to_shiftimm(
     input_to_const(ctx, input).and_then(ShiftOpShiftImm::maybe_from_shift)
 }
 
-pub(crate) fn const_param_to_u128(ctx: &mut Lower<Inst>, inst: IRInst) -> Option<u128> {
-    match ctx.get_immediate(inst) {
-        Some(DataValue::V128(bytes)) => Some(u128::from_le_bytes(bytes)),
-        _ => None,
-    }
-}
-
 /// How to handle narrow values loaded into registers; see note on `narrow_mode`
 /// parameter to `put_input_in_*` below.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]

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

@@ -5,9 +5,9 @@ pub mod generated_code;
 
 // Types that the generated ISLE code uses via `use super::*`.
 use super::{
-    insn_inputs, lower_constant_f128, writable_zero_reg, zero_reg, AMode, ASIMDFPModImm,
-    ASIMDMovModImm, BranchTarget, CallIndInfo, CallInfo, Cond, CondBrKind, ExtendOp, FPUOpRI,
-    FloatCC, Imm12, ImmLogic, ImmShift, Inst as MInst, IntCC, JTSequenceInfo, MachLabel,
+    insn_inputs, lower_constant_f128, lower_constant_f64, writable_zero_reg, zero_reg, AMode,
+    ASIMDFPModImm, ASIMDMovModImm, BranchTarget, CallIndInfo, CallInfo, Cond, CondBrKind, ExtendOp,
+    FPUOpRI, FloatCC, Imm12, ImmLogic, ImmShift, Inst as MInst, IntCC, JTSequenceInfo, MachLabel,
     MoveWideConst, MoveWideOp, NarrowValueMode, Opcode, OperandSize, PairAMode, Reg, ScalarSize,
     ShiftOpAndAmt, UImm5, VecMisc2, VectorSize, NZCV,
 };
@@ -484,6 +484,14 @@ impl generated_code::Context for IsleContext<'_, '_, MInst, Flags, IsaFlags, 6>
         address.is_reg()
     }
 
+    fn constant_f64(&mut self, value: u64) -> Reg {
+        let rd = self.temp_writable_reg(I8X16);
+
+        lower_constant_f64(self.lower_ctx, rd, f64::from_bits(value));
+
+        rd.to_reg()
+    }
+
     fn constant_f128(&mut self, value: u128) -> Reg {
         let rd = self.temp_writable_reg(I8X16);
 

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

@@ -644,11 +644,7 @@ pub(crate) fn lower_insn_to_regs(
             panic!("Branch opcode reached non-branch lowering logic!");
         }
 
-        Opcode::Vconst => {
-            let value = const_param_to_u128(ctx, insn).expect("Invalid immediate bytes");
-            let rd = get_output_reg(ctx, outputs[0]).only_reg().unwrap();
-            lower_constant_f128(ctx, rd, value);
-        }
+        Opcode::Vconst => implemented_in_isle(ctx),
 
         Opcode::RawBitcast => {
             let rm = put_input_in_reg(ctx, inputs[0], NarrowValueMode::None);

cranelift/codegen/src/machinst/isle.rs

@@ -683,6 +683,12 @@ macro_rules! isle_prelude_methods {
             Some(u128::from_le_bytes(bytes.try_into().ok()?))
         }
 
+        #[inline]
+        fn u64_from_constant(&mut self, constant: Constant) -> Option<u64> {
+            let bytes = self.lower_ctx.get_constant_data(constant).as_slice();
+            Some(u64::from_le_bytes(bytes.try_into().ok()?))
+        }
+
         #[inline]
         fn u128_from_constant(&mut self, constant: Constant) -> Option<u128> {
             let bytes = self.lower_ctx.get_constant_data(constant).as_slice();

cranelift/codegen/src/machinst/lower.rs

@@ -1387,15 +1387,23 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
         let inst_data = self.data(ir_inst);
         match inst_data {
             InstructionData::Shuffle { imm, .. } => {
-                let buffer = self.f.dfg.immediates.get(imm.clone()).unwrap().as_slice();
-                let value = DataValue::V128(buffer.try_into().expect("a 16-byte data buffer"));
+                let mask = self.f.dfg.immediates.get(imm.clone()).unwrap().as_slice();
+                let value = match mask.len() {
+                    16 => DataValue::V128(mask.try_into().expect("a 16-byte vector mask")),
+                    8 => DataValue::V64(mask.try_into().expect("an 8-byte vector mask")),
+                    length => panic!("unexpected Shuffle mask length {}", length),
+                };
                 Some(value)
             }
             InstructionData::UnaryConst {
                 constant_handle, ..
             } => {
                 let buffer = self.f.dfg.constants.get(constant_handle.clone()).as_slice();
-                let value = DataValue::V128(buffer.try_into().expect("a 16-byte data buffer"));
+                let value = match buffer.len() {
+                    16 => DataValue::V128(buffer.try_into().expect("a 16-byte data buffer")),
+                    8 => DataValue::V64(buffer.try_into().expect("an 8-byte data buffer")),
+                    length => panic!("unexpected UnaryConst buffer length {}", length),
+                };
                 Some(value)
             }
             _ => inst_data.imm_value(),

cranelift/codegen/src/prelude.isle

@@ -799,6 +799,11 @@
 (decl u128_from_constant (u128) Constant)
 (extern extractor u128_from_constant u128_from_constant)
 
+;; Accessor for `Constant` as u64.
+
+(decl u64_from_constant (u64) Constant)
+(extern extractor u64_from_constant u64_from_constant)
+
 
 ;;;; Helpers for tail recursion loops ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 

cranelift/filetests/filetests/runtests/simd-vconst-64bit.clif

@@ -0,0 +1,39 @@
+test interpret
+test run
+target aarch64
+; x86_64 and s390x do not support 64-bit vectors.
+
+function %vconst_zeroes() -> i8x8 {
+block0:
+    v0 = vconst.i8x8 0x00
+    return v0
+}
+; run: %vconst_zeroes() == [0 0 0 0 0 0 0 0]
+
+function %vconst_ones() -> i8x8 {
+block0:
+    v0 = vconst.i8x8 0xffffffffffffffff
+    return v0
+}
+; run: %vconst_ones() == [255 255 255 255 255 255 255 255]
+
+function %vconst_i8x8() -> i8x8 {
+block0:
+    v0 = vconst.i8x8 [0 31 63 95 127 159 191 255]
+    return v0
+}
+; run: %vconst_i8x8() == [0 31 63 95 127 159 191 255]
+
+function %vconst_i16x4() -> i16x4 {
+block0:
+    v0 = vconst.i16x4 [0 255 32767 65535]
+    return v0
+}
+; run: %vconst_i16x4() == [0 255 32767 65535]
+
+function %vconst_i32x2() -> i32x2 {
+block0:
+    v0 = vconst.i32x2 [0 4294967295]
+    return v0
+}
+; run: %vconst_i32x2() == [0 4294967295]

cranelift/interpreter/src/step.rs

@@ -75,7 +75,11 @@ where
                     .constants
                     .get(constant_handle.clone())
                     .as_slice();
-                DataValue::V128(buffer.try_into().expect("a 16-byte data buffer"))
+                match ctrl_ty.bytes() {
+                    16 => DataValue::V128(buffer.try_into().expect("a 16-byte data buffer")),
+                    8 => DataValue::V64(buffer.try_into().expect("an 8-byte data buffer")),
+                    length => panic!("unexpected UnaryConst buffer length {}", length),
+                }
             }
             InstructionData::Shuffle { imm, .. } => {
                 let mask = state
@@ -85,7 +89,11 @@ where
                     .get(imm)
                     .unwrap()
                     .as_slice();
-                DataValue::V128(mask.try_into().expect("a 16-byte vector mask"))
+                match ctrl_ty.bytes() {
+                    16 => DataValue::V128(mask.try_into().expect("a 16-byte vector mask")),
+                    8 => DataValue::V64(mask.try_into().expect("an 8-byte vector mask")),
+                    length => panic!("unexpected Shuffle mask length {}", length),
+                }
             }
             _ => inst.imm_value().unwrap(),
         })