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Fix some 16- and 8-bit behavior in x64 backend related to rotates.

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Uncovered by @bjorn3 (thanks!): 8- and 16-bit rotates were not working
properly in recent versions of Cranelift with part of the lowering
migrated to ISLE.

This PR fixes a few issues:

- 8- and 16-bit rotate-left needs to mask a constant amount, if any,
  because we use a 32-bit rotate instruction and so don't get the
  appropriate shift-amount masking for free from x86 semantics.

- `operand_size_from_type` was incorrect: it only handled 32- and 64-bit
  types and silently returned `OperandSize::Size32` for everything else.
  Now uses the `OperandSize::from_ty(ty)` helper as the pre-ISLE code
  did.

Our test coverage for narrow value types is not great; this PR adds some
runtests for rotl/rotr but more would always be better!
This commit is contained in:
Chris Fallin
2021-12-16 11:34:24 -08:00
parent d29b7c8a59
commit 1323ae417e
10 changed files with 352 additions and 229 deletions
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17
cranelift/codegen/src/isa/x64/lower.isle
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@@ -633,15 +633,26 @@
;;;; Rules for `rotl` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; `i64` and smaller.
;; `i16` and `i8`: we need to extend the shift amount, or mask the
;; constant.
(rule (lower (has_type (fits_in_64 ty) (rotl src amt)))
(rule (lower (has_type (ty_8_or_16 ty) (rotl src amt)))
(let ((amt_ Reg (extend_to_reg amt $I32 (ExtendKind.Zero))))
(value_reg (m_rotl ty (put_in_reg src) (Imm8Reg.Reg amt_)))))
(rule (lower (has_type (ty_8_or_16 ty) (rotl src (imm8_from_value amt))))
(value_reg (m_rotl ty (put_in_reg src) (mask_imm8_const amt (ty_bits_mask ty)))))
;; `i64` and `i32`: we can rely on x86's rotate-amount masking since
;; we operate on the whole register.
(rule (lower (has_type (ty_32_or_64 ty) (rotl src amt)))
;; NB: Only the low bits of `amt` matter since we logically mask the
;; shift amount to the value's bit width.
(let ((amt_ Reg (lo_reg amt)))
(value_reg (m_rotl ty (put_in_reg src) (Imm8Reg.Reg amt_)))))
(rule (lower (has_type (fits_in_64 ty) (rotl src (imm8_from_value amt))))
(rule (lower (has_type (ty_32_or_64 ty) (rotl src (imm8_from_value amt))))
(value_reg (m_rotl ty (put_in_reg src) amt)))
;; `i128`.