64-bit LoongArch has native CRC instructions for two specific
polynomials. For other polynomials or 32-bit, use the generic
table-based approach but optimize bit reversing.
gcc/ChangeLog:
* config/loongarch/loongarch.md (crc_rev<mode:SUBDI>si4): New
define_expand.
---
gcc/config/loongarch/loongarch.md | 57 +++++++++++++++++++++++++++++++
1 file changed, 57 insertions(+)
diff --git a/gcc/config/loongarch/loongarch.md
b/gcc/config/loongarch/loongarch.md
index fe1678c5891..806b0ec0be9 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -4420,6 +4420,63 @@ (define_insn "loongarch_<crc>_w_<size>_w_extended"
[(set_attr "type" "unknown")
(set_attr "mode" "<MODE>")])
+(define_expand "crc_rev<mode>si4"
+ [(match_operand:SI 0 "register_operand") ; new_chksum
+ (match_operand:SI 1 "register_operand") ; old_chksum
+ (match_operand:SUBDI 2 "reg_or_0_operand") ; msg
+ (match_operand 3 "const_int_operand")] ; poly
+ ""
+ {
+ unsigned HOST_WIDE_INT poly = UINTVAL (operands[3]);
+ rtx msg = operands[2];
+ rtx (*crc_insn)(rtx, rtx, rtx) = nullptr;
+
+ /* TODO: Review this when adding LA32 support. If we're going to
+ support CRC instructions on LA32 we'll need a "-mcrc" switch as
+ they are optional on LA32. */
+
+ if (TARGET_64BIT)
+ {
+ if (poly == reflect_hwi (0xedb88320u, 32))
+ crc_insn = gen_loongarch_crc_w_<size>_w;
+ else if (poly == reflect_hwi (0x82f63b78u, 32))
+ crc_insn = gen_loongarch_crcc_w_<size>_w;
+ }
+
+ if (crc_insn)
+ {
+ /* We cannot make crc_insn to accept const0_rtx easily:
+ it's not possible to figure out the mode of const0_rtx so we'd
+ have to separate both UNSPEC_CRC and UNSPEC_CRCC to 4 different
+ UNSPECs. Instead just hack it around here. */
+ if (msg == const0_rtx)
+ msg = gen_rtx_REG (<MODE>mode, 0);
+
+ emit_insn (crc_insn (operands[0], msg, operands[1]));
+ }
+ else
+ {
+ /* No CRC instruction is suitable, use the generic table-based
+ implementation but optimize bit reversion. */
+ auto rbit = [](rtx *r)
+ {
+ /* Well, this is ugly. The problem is
+ expand_reversed_crc_table_based only accepts one helper
+ for reversing data elements and CRC states. */
+ auto mode = GET_MODE (*r);
+ auto rbit = (mode == <MODE>mode ? gen_rbit<mode> : gen_rbitsi);
+ rtx out = gen_reg_rtx (mode);
+
+ emit_insn (rbit (out, *r));
+ *r = out;
+ };
+ expand_reversed_crc_table_based (operands[0], operands[1],
+ msg, operands[3], <MODE>mode,
+ rbit);
+ }
+ DONE;
+ })
+
;; With normal or medium code models, if the only use of a pc-relative
;; address is for loading or storing a value, then relying on linker
;; relaxation is not better than emitting the machine instruction directly.
--
2.47.1
