[Bug target/116999] New: Fold SVE whilelt/le comparisons with max int value to ptrue

[ktkachov at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116999

            Bug ID: 116999
           Summary: Fold SVE whilelt/le comparisons with max int value to
                    ptrue
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

Example testcase:
#include <arm_sve.h>
#include <climits>


svbool_t
foo_s32_le (int32_t x)
{
  return svwhilele_b64_s32 (x, INT_MAX);
}

svbool_t
foo_s64_le (int64_t x)
{
  return svwhilele_b64_s64 (x, LONG_LONG_MAX);
}

can avoid generating the WHILELE instructions and just generate a PTRUE.
This is as per the WHILELE documentation:
"If the second scalar operand is equal to the maximum signed integer value then
a condition which includes an equality test can never fail and the result will
be an all-true predicate."

Note that we probably want to look at the use of the flags from the whilele as
well. If we cannot prove that the NZCV are unused then we have to generate a
PTRUES instead, I think