[Bug target/67459] New: [SH]=?UTF-8?Q?=C2=A0addc?=/subc/negc set of T reg rtx seem wrong

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67459

            Bug ID: 67459
           Summary: [SH] addc/subc/negc set of T reg rtx seem wrong
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olegendo at gcc dot gnu.org
  Target Milestone: ---
            Target: sh*-*-*

The following should be verified.
Currently there is no problem because nothing in GCC understands or uses the
exact T reg values.  However, clrt/sett optimization might want to do that in
the future, for which correct set rtxes are needed in the insns.

addc:
   (set (reg:SI T_REG)
        (ltu:SI (plus:SI (match_dup 1) (match_dup 2)) (match_dup 1)))]

The insn operation description says (comparisons are unsigned):
  if (R[n] > R[n] + R[m])
    T = 1;
  else if (R[n] + R[m] > R[n] + R[m] + T)
    T = 1;
  else
    T = 0;

which could probably be simplified a bit.

subc:
   (set (reg:SI T_REG)
        (gtu:SI (minus:SI (minus:SI (match_dup 1) (match_dup 2))
                          (reg:SI T_REG))
                (match_dup 1)))]

The insn operation description says (comparisons are unsigned):
  if (R[n] < R[n] - R[m])
    T = 1;
  else if (R[n] - R[m] < R[n] - R[m] - T)
    T = 1;
  else
    T = 0;


negc:
   (set (reg:SI T_REG)
        (ne:SI (ior:SI (reg:SI T_REG) (match_dup 1))
               (const_int 0)))]

The insn operation description says:
  if (0 < 0 - R[m])
    T = 1;
  else if (0 - R[m] - T < R[n])
    T = 1;
  else
    T = 0;