ISLE: remove all uses of argument polarity, and remove it from the language. (#4091)

This PR removes "argument polarity": the feature of ISLE extractors that lets them take
inputs aside from the value to be matched.

Cases that need this expressivity have been subsumed by #4072 with if-let clauses;
we can now finally remove this misfeature of the language, which has caused significant
confusion and has always felt like a bit of a hack.

This PR (i) removes the feature from the ISLE compiler; (ii) removes it from the reference
documentation; and (iii) refactors away all uses of the feature in our three existing
backends written in ISLE.

cranelift/codegen/src/isa/x64/inst.isle

@@ -793,8 +793,8 @@
 ;; A helper to both check that the `Imm64` and `Offset32` values sum to less
 ;; than 32-bits AND return this summed `u32` value. Also, the `Imm64` will be
 ;; zero-extended from `Type` up to 64 bits. This is useful for `to_amode`.
-(decl sum_extend_fits_in_32_bits (Type Imm64 u32) Offset32)
-(extern extractor sum_extend_fits_in_32_bits sum_extend_fits_in_32_bits (in in out))
+(decl pure sum_extend_fits_in_32_bits (Type Imm64 Offset32) u32)
+(extern constructor sum_extend_fits_in_32_bits sum_extend_fits_in_32_bits)
 
 ;; To generate an address for a memory access, we can pattern-match various CLIF
 ;; sub-trees to x64's complex addressing modes (`Amode`). In pseudo-code:
@@ -828,14 +828,18 @@
 ;; extractor to check that the offset and constant value (`c`, the in
 ;; parameter), when summed will fit into x64's 32-bit displacement, returned as
 ;; `sum` (the out parameter). The syntax for this could be improved (TODO).
-(rule (to_amode flags (iadd (iconst c) base) _offset @ (sum_extend_fits_in_32_bits <$I64 <c sum))
+(rule (to_amode flags (iadd (iconst c) base) offset)
+      (if-let sum (sum_extend_fits_in_32_bits $I64 c offset))
       (amode_imm_reg_flags sum (put_in_gpr base) flags))
-(rule (to_amode flags (iadd base (iconst c)) _offset @ (sum_extend_fits_in_32_bits <$I64 <c sum))
+(rule (to_amode flags (iadd base (iconst c)) offset)
+      (if-let sum (sum_extend_fits_in_32_bits $I64 c offset))
       (amode_imm_reg_flags sum (put_in_gpr base) flags))
 ;; ...matches (uextend(iconst c) ...); see notes above.
-(rule (to_amode flags (iadd (has_type ty (uextend (iconst c))) base) _offset @ (sum_extend_fits_in_32_bits <ty <c sum))
+(rule (to_amode flags (iadd (has_type ty (uextend (iconst c))) base) offset)
+      (if-let sum (sum_extend_fits_in_32_bits $I64 c offset))
       (amode_imm_reg_flags sum (put_in_gpr base) flags))
-(rule (to_amode flags (iadd base (has_type ty (uextend (iconst c)))) _offset @ (sum_extend_fits_in_32_bits <ty <c sum))
+(rule (to_amode flags (iadd base (has_type ty (uextend (iconst c)))) offset)
+      (if-let sum (sum_extend_fits_in_32_bits $I64 c offset))
       (amode_imm_reg_flags sum (put_in_gpr base) flags))
 ;; ...else only matches (iadd(a b))
 (rule (to_amode flags (iadd base index) offset)

cranelift/codegen/src/isa/x64/lower/isle.rs

@@ -526,9 +526,9 @@ where
     #[inline]
     fn sum_extend_fits_in_32_bits(
         &mut self,
-        offset: Offset32,
         extend_from_ty: Type,
         constant_value: Imm64,
+        offset: Offset32,
     ) -> Option<u32> {
         let offset: i64 = offset.into();
         let constant_value: u64 = constant_value.bits() as u64;

cranelift/codegen/src/isa/x64/lower/isle/generated_code.manifest

@@ -1,4 +1,4 @@
 src/clif.isle 443b34b797fc8ace
 src/prelude.isle a7915a6b88310eb5
-src/isa/x64/inst.isle a63b8ede292f2e20
+src/isa/x64/inst.isle 65f15f51eefe0ce3
 src/isa/x64/lower.isle 4c567e9157f84afb