cranelift: Remove redundant branch and select instructions (#5097)

As discussed in the 2022/10/19 meeting, this PR removes many of the branch and select instructions that used iflags, in favor if using brz/brnz and select in their place. Additionally, it reworks selectif_spectre_guard to take an i8 input instead of an iflags input.

For reference, the removed instructions are: br_icmp, brif, brff, trueif, trueff, and selectif.

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

@@ -1089,12 +1089,6 @@
 (decl cc_invert (CC) CC)
 (extern constructor cc_invert cc_invert)
 
-(decl intcc_reverse (IntCC) IntCC)
-(extern constructor intcc_reverse intcc_reverse)
-
-(decl floatcc_inverse (FloatCC) FloatCC)
-(extern constructor floatcc_inverse floatcc_inverse)
-
 ;; Fails if the argument is not either CC.NZ or CC.Z.
 (decl cc_nz_or_z (CC) CC)
 (extern extractor cc_nz_or_z cc_nz_or_z)

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

@@ -2760,16 +2760,6 @@
 (rule (lower_branch (jump _ _) (single_target target))
       (side_effect (jmp_known target)))
 
-;; Rules for `brif` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
-(rule (lower_branch (brif cc (ifcmp a b) _ _) (two_targets taken not_taken))
-      (side_effect (jmp_cond_icmp (emit_cmp cc a b) taken not_taken)))
-
-;; Rules for `brff` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
-(rule (lower_branch (brff cc (ffcmp a b) _ _) (two_targets taken not_taken))
-      (side_effect (jmp_cond_fcmp (emit_fcmp cc a b) taken not_taken)))
-
 ;; Rules for `brz` and `brnz` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (rule 2 (lower_branch (brz (icmp cc a b) _ _) (two_targets taken not_taken))
@@ -2828,22 +2818,14 @@
             (src Gpr val))
         (x64_test size src src)))
 
-;; Rules for `bricmp` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
-(rule (lower_branch (br_icmp cc a b _ _) (two_targets taken not_taken))
-      (side_effect (jmp_cond_icmp (emit_cmp cc a b) taken not_taken)))
-
 ;; Rules for `br_table` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (rule (lower_branch (br_table idx @ (value_type ty) _ _) (jump_table_targets default_target jt_targets))
       (side_effect (jmp_table_seq ty idx default_target jt_targets)))
 
-;; Rules for `selectif` and `selectif_spectre_guard` ;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Rules for `select_spectre_guard` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
-(rule (lower (selectif cc (ifcmp a b) x y))
-      (select_icmp (emit_cmp cc a b) x y))
-
-(rule (lower (selectif_spectre_guard cc (ifcmp a b) x y))
+(rule (lower (select_spectre_guard (icmp cc a b) x y))
       (select_icmp (emit_cmp cc a b) x y))
 
 ;; Rules for `fcvt_from_sint` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

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

@@ -419,8 +419,7 @@ fn lower_insn_to_regs(
         | Opcode::GetStackPointer
         | Opcode::GetReturnAddress
         | Opcode::Select
-        | Opcode::Selectif
-        | Opcode::SelectifSpectreGuard
+        | Opcode::SelectSpectreGuard
         | Opcode::FcvtFromSint
         | Opcode::FcvtLowFromSint
         | Opcode::FcvtFromUint
@@ -499,8 +498,6 @@ fn lower_insn_to_regs(
 
         Opcode::Bmask => unimplemented!("Bmask not implemented"),
 
-        Opcode::Trueif | Opcode::Trueff => unimplemented!("trueif / trueff not implemented"),
-
         Opcode::Vsplit | Opcode::Vconcat => {
             unimplemented!("Vector split/concat ops not implemented.");
         }
@@ -570,13 +567,7 @@ fn lower_insn_to_regs(
             panic!("trapz / trapnz / resumable_trapnz should have been removed by legalization!");
         }
 
-        Opcode::Jump
-        | Opcode::Brz
-        | Opcode::Brnz
-        | Opcode::BrIcmp
-        | Opcode::Brif
-        | Opcode::Brff
-        | Opcode::BrTable => {
+        Opcode::Jump | Opcode::Brz | Opcode::Brnz | Opcode::BrTable => {
             panic!("Branch opcode reached non-branch lowering logic!");
         }
     }

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

@@ -593,16 +593,6 @@ impl Context for IsleContext<'_, '_, MInst, Flags, IsaFlags, 6> {
         }
     }
 
-    #[inline]
-    fn intcc_reverse(&mut self, cc: &IntCC) -> IntCC {
-        cc.reverse()
-    }
-
-    #[inline]
-    fn floatcc_inverse(&mut self, cc: &FloatCC) -> FloatCC {
-        cc.inverse()
-    }
-
     #[inline]
     fn sum_extend_fits_in_32_bits(
         &mut self,