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

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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.
This commit is contained in:
Trevor Elliott
2022-10-24 16:14:35 -07:00
committed by GitHub
parent 30589170b4
commit ec12415b1f
40 changed files with 579 additions and 2527 deletions
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17
cranelift/codegen/src/isa/s390x/lower.isle
View File

@@ -3726,15 +3726,15 @@
(put_in_reg val_true) (put_in_reg val_false)))
;;;; Rules for `selectif_spectre_guard` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Rules for `select_spectre_guard` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; We do not support the `iflags` mechanism on our platform. However, common
;; code will unconditionally emit certain patterns using `iflags` which we
;; need to handle somehow. Note that only those specific patterns are
;; recognized by the code below, other uses will fail to lower.
(rule (lower (has_type ty (selectif_spectre_guard int_cc
(ifcmp x y) val_true val_false)))
(rule (lower (has_type ty (select_spectre_guard
(icmp int_cc x y) val_true val_false)))
(select_bool_reg ty (icmp_val $false int_cc x y)
(put_in_reg val_true) (put_in_reg val_false)))
@@ -3801,17 +3801,6 @@
(vec_element targets 1))))
;;;; Rules for `brif` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Similarly to `selectif_spectre_guard`, we only recognize specific patterns
;; generated by common code here. Others will fail to lower.
(rule (lower_branch (brif int_cc (ifcmp x y) _ _) targets)
(side_effect (cond_br_bool (icmp_val $false int_cc x y)
(vec_element targets 0)
(vec_element targets 1))))
;;;; Rules for `trap` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(rule (lower (trap trap_code))

17
cranelift/codegen/src/isa/s390x/lower.rs
View File

@@ -171,7 +171,7 @@ impl LowerBackend for S390xBackend {
| Opcode::IsNull
| Opcode::IsInvalid
| Opcode::Select
| Opcode::SelectifSpectreGuard
| Opcode::SelectSpectreGuard
| Opcode::Trap
| Opcode::ResumableTrap
| Opcode::Trapz
@@ -223,21 +223,10 @@ impl LowerBackend for S390xBackend {
Opcode::GlobalValue => {
panic!("global_value should have been removed by legalization!");
}
Opcode::Ifcmp
| Opcode::Ffcmp
| Opcode::Trapff
| Opcode::Trueif
| Opcode::Trueff
| Opcode::Selectif => {
Opcode::Ifcmp | Opcode::Ffcmp | Opcode::Trapff => {
panic!("Flags opcode should not be encountered.");
}
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!");
}
Opcode::IaddImm