aarch64: Migrate popcnt to ISLE (#3662)

Nothing too unusual here, the translation was quite straightforward!

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

@@ -1421,6 +1421,13 @@
             (_ Unit (emit (MInst.VecRRR op dst src1 src2 size))))
         (writable_reg_to_reg dst)))
 
+;; Helper for emitting `MInst.VecLanes` instructions.
+(decl vec_lanes (VecLanesOp Reg VectorSize) Reg)
+(rule (vec_lanes op src size)
+      (let ((dst WritableReg (temp_writable_reg $I8X16))
+            (_ Unit (emit (MInst.VecLanes op dst src size))))
+        (writable_reg_to_reg dst)))
+
 ;; Helper for emitting `MInst.VecDup` instructions.
 (decl vec_dup (Reg VectorSize) Reg)
 (rule (vec_dup src size)
@@ -1543,6 +1550,21 @@
             (_ Unit (emit (MInst.VecRRLong op dst src high_half))))
         (writable_reg_to_reg dst)))
 
+;; Helper for emitting `MInst.MovToFpu` instructions.
+(decl mov_to_fpu (Reg ScalarSize) Reg)
+(rule (mov_to_fpu x size)
+      (let ((dst WritableReg (temp_writable_reg $I8X16))
+            (_ Unit (emit (MInst.MovToFpu dst x size))))
+        (writable_reg_to_reg dst)))
+
+;; Helper for emitting `MInst.MovToVec` instructions.
+(decl mov_to_vec (Reg Reg u8 VectorSize) Reg)
+(rule (mov_to_vec src1 src2 lane size)
+      (let ((dst WritableReg (temp_writable_reg $I8X16))
+            (_1 Unit (emit (MInst.FpuMove128 dst src1)))
+            (_2 Unit (emit (MInst.MovToVec dst src2 lane size))))
+        (writable_reg_to_reg dst)))
+
 ;; Helper for emitting `MInst.MovFromVec` instructions.
 (decl mov_from_vec (Reg u8 VectorSize) Reg)
 (rule (mov_from_vec rn idx size)
@@ -1745,6 +1767,10 @@
 (decl addp (Reg Reg VectorSize) Reg)
 (rule (addp x y size) (vec_rrr (VecALUOp.Addp) x y size))
 
+;; Helper for generating `addv` instructions.
+(decl addv (Reg VectorSize) Reg)
+(rule (addv x size) (vec_lanes (VecLanesOp.Addv) x size))
+
 ;; Helper for generating `shll32` instructions.
 (decl shll32 (Reg bool) Reg)
 (rule (shll32 x high_half) (vec_rr_long (VecRRLongOp.Shll32) x high_half))
@@ -1931,6 +1957,11 @@
 (decl eon64 (Reg Reg) Reg)
 (rule (eon64 x y) (alu_rrr (ALUOp.EorNot64) x y))
 
+;; Helpers for generating `cnt` instructions.
+
+(decl vec_cnt (Reg VectorSize) Reg)
+(rule (vec_cnt x size) (vec_misc (VecMisc2.Cnt) x size))
+
 ;; Immediate value helpers ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (decl imm (Type u64) Reg)

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

@@ -1129,3 +1129,67 @@
           ))
         )
         (value_regs (add64 maybe_lo hi_cls) (imm $I64 0))))
+
+;;;; Rules for `popcnt` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; The implementation of `popcnt` for scalar types is done by moving the value
+;; into a vector register, using the `cnt` instruction, and then collating the
+;; result back into a normal register.
+;;
+;; The general sequence emitted here is
+;;
+;;     fmov tmp, in_lo
+;;     if ty == i128:
+;;         mov tmp.d[1], in_hi
+;;
+;;     cnt tmp.16b, tmp.16b / cnt tmp.8b, tmp.8b
+;;     addv tmp, tmp.16b / addv tmp, tmp.8b / addp tmp.8b, tmp.8b, tmp.8b / (no instruction for 8-bit inputs)
+;;
+;;     umov out_lo, tmp.b[0]
+;;     if ty == i128:
+;;         mov out_hi, 0
+
+(rule (lower (has_type $I8 (popcnt x)))
+      (let (
+          (tmp Reg (mov_to_fpu (put_in_reg x) (ScalarSize.Size32)))
+          (nbits Reg (vec_cnt tmp (VectorSize.Size8x8)))
+        )
+        (value_reg (mov_from_vec nbits 0 (VectorSize.Size8x16)))))
+
+;; Note that this uses `addp` instead of `addv` as it's usually cheaper.
+(rule (lower (has_type $I16 (popcnt x)))
+      (let (
+          (tmp Reg (mov_to_fpu (put_in_reg x) (ScalarSize.Size32)))
+          (nbits Reg (vec_cnt tmp (VectorSize.Size8x8)))
+          (added Reg (addp nbits nbits (VectorSize.Size8x8)))
+        )
+        (value_reg (mov_from_vec added 0 (VectorSize.Size8x16)))))
+
+(rule (lower (has_type $I32 (popcnt x)))
+      (let (
+          (tmp Reg (mov_to_fpu (put_in_reg x) (ScalarSize.Size32)))
+          (nbits Reg (vec_cnt tmp (VectorSize.Size8x8)))
+          (added Reg (addv nbits (VectorSize.Size8x8)))
+        )
+        (value_reg (mov_from_vec added 0 (VectorSize.Size8x16)))))
+
+(rule (lower (has_type $I64 (popcnt x)))
+      (let (
+          (tmp Reg (mov_to_fpu (put_in_reg x) (ScalarSize.Size64)))
+          (nbits Reg (vec_cnt tmp (VectorSize.Size8x8)))
+          (added Reg (addv nbits (VectorSize.Size8x8)))
+        )
+        (value_reg (mov_from_vec added 0 (VectorSize.Size8x16)))))
+
+(rule (lower (has_type $I128 (popcnt x)))
+      (let (
+          (val ValueRegs (put_in_regs x))
+          (tmp_half Reg (mov_to_fpu (value_regs_get val 0) (ScalarSize.Size64)))
+          (tmp Reg (mov_to_vec tmp_half (value_regs_get val 1) 1 (VectorSize.Size64x2)))
+          (nbits Reg (vec_cnt tmp (VectorSize.Size8x16)))
+          (added Reg (addv nbits (VectorSize.Size8x16)))
+        )
+        (value_regs (mov_from_vec added 0 (VectorSize.Size8x16)) (imm $I64 0))))
+
+(rule (lower (has_type $I8X16 (popcnt x)))
+      (value_reg (vec_cnt (put_in_reg x) (VectorSize.Size8x16))))

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

@@ -1,4 +1,4 @@
 src/clif.isle f176ef3bba99365
 src/prelude.isle babc931e5dc5b4cf
-src/isa/aarch64/inst.isle 3ae25d431916bb81
-src/isa/aarch64/lower.isle 5715ecb7c7a41164
+src/isa/aarch64/inst.isle 5fa80451697b084f
+src/isa/aarch64/lower.isle 2d2e1e076a0c8a23