aarch64: int min max (bytecodealliance#161)

Verify integer min/max.

These rules are a great demonstration of the new priority support, since
the correctness of the `cmp_and_choose` helper rule for `fits_in_64`
relies on the higher priority 16-bit case.

Updates bytecodealliance#128

cranelift/codegen/src/inst_specs.isle

@@ -220,3 +220,19 @@
 (spec (sextend x)
     (match (= result (sign_ext (widthof result) x))))
 (instantiate sextend extend)
+
+(spec (smin x y)
+    (match (= result (if (bvsle x y) x y))))
+(instantiate smin bv_binary_8_to_64)
+
+(spec (umin x y)
+    (match (= result (if (bvule x y) x y))))
+(instantiate umin bv_binary_8_to_64)
+
+(spec (smax x y)
+    (provide (= result (if (bvsge x y) x y))))
+(instantiate smax bv_binary_8_to_64)
+
+(spec (umax x y)
+    (provide (= result (if (bvuge x y) x y))))
+(instantiate umax bv_binary_8_to_64)

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

@@ -2192,7 +2192,7 @@
 (extern constructor writable_link_reg writable_link_reg)
 
 (decl writable_zero_reg () WritableReg)
-(spec (writable_zero_reg) (provide (= (zero_ext (widthof result) #b0) result)))
+(spec (writable_zero_reg) (provide true)) ; zero register is just a write sink
 (extern constructor writable_zero_reg writable_zero_reg)
 
 (decl value_regs_zero () ValueRegs)

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

@@ -1122,11 +1122,14 @@
 ;; cmp     $x, $y
 ;; csel    .., $x, $y, $cc
 (decl cmp_and_choose (Type Cond bool Value Value) ValueRegs)
-(rule (cmp_and_choose (fits_in_64 ty) cc _ x y)
+(attr cmp_and_choose (veri chain))
+(rule cmp_and_choose_64
+      (cmp_and_choose (fits_in_64 ty) cc _ x y)
       (let ((x Reg (put_in_reg x))
             (y Reg (put_in_reg y)))
        (with_flags_reg (cmp (operand_size ty) x y)
                        (csel cc x y))))
+(attr cmp_and_choose_64 (veri priority))
 
 ;; `i16` and `i8` min/max require sign extension as
 ;; the comparison operates on (at least) 32 bits.
@@ -1136,13 +1139,13 @@
       (with_flags_reg (cmp (operand_size ty) x y)
                       (csel cc x y))))
 
-(rule 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (umin x y)))
+(rule umin 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (umin x y)))
       (cmp_and_choose ty (Cond.Lo) $false x y))
-(rule 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (smin x y)))
+(rule smin 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (smin x y)))
       (cmp_and_choose ty (Cond.Lt) $true x y))
-(rule 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (umax x y)))
+(rule umax 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (umax x y)))
       (cmp_and_choose ty (Cond.Hi) $false x y))
-(rule 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (smax x y)))
+(rule smax 2 (lower (has_type (and (fits_in_64 ty) (ty_int _)) (smax x y)))
       (cmp_and_choose ty (Cond.Gt) $true x y))
 
 ;; Vector types.

cranelift/codegen/src/prelude.isle

@@ -638,6 +638,7 @@
 ;; An extractor that only matches integers.
 (decl ty_int (Type) Type)
 (extern extractor ty_int ty_int)
+(spec (ty_int arg) (provide (= arg result)))
 
 ;; An extractor that only matches scalar types, float or int or ref's.
 (decl ty_scalar (Type) Type)