[Bug target/114402] New: rs6000: ICE when long double is ieee128 format by default but without vsx

[Bug target/114402] New: rs6000: ICE when long double is ieee128 format by default but without vsx

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114402

            Bug ID: 114402
           Summary: rs6000: ICE when long double is ieee128 format by
                    default but without vsx
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: linkw at gcc dot gnu.org
  Target Milestone: ---

When I was doing a patch to make us only have two 128bit fp on rs6000, I found
that we can have long double with ieee128 format by default and even not having
vsx support, but a simple test case with comparison triggers ICE as below:

long double a;
long double b;

int foo() {
  if (a > b)
    return 0;
  else
    return 1;
}

/opt/gcc-nightly/trunk/bin/gcc test.c -mno-vsx

test.c: In function ‘foo’:
test.c:9:1: error: unrecognizable insn:
    9 | }
      | ^
(insn 9 8 10 2 (set (reg:CCFP 123)
        (compare:CCFP (reg:TF 117 [ a.0_1 ])
            (reg:TF 118 [ b.1_2 ]))) "test.c":5:6 -1
     (nil))
during RTL pass: vregs
test.c:9:1: internal compiler error: in extract_insn, at recog.cc:2812
0x102b7353 _fatal_insn(char const*, rtx_def const*, char const*, int, char
const*)
        /home/gccbuild/gcc_trunk_git/gcc/gcc/rtl-error.cc:108
0x102b73a7 _fatal_insn_not_found(rtx_def const*, char const*, int, char const*)
        /home/gccbuild/gcc_trunk_git/gcc/gcc/rtl-error.cc:116
0x10c6636b extract_insn(rtx_insn*)
        /home/gccbuild/gcc_trunk_git/gcc/gcc/recog.cc:2812
0x107ef797 instantiate_virtual_regs_in_insn
        /home/gccbuild/gcc_trunk_git/gcc/gcc/function.cc:1611
0x107ef797 instantiate_virtual_regs
        /home/gccbuild/gcc_trunk_git/gcc/gcc/function.cc:1994
0x107ef797 execute
        /home/gccbuild/gcc_trunk_git/gcc/gcc/function.cc:2041
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

Note that it should be configured with --with-long-double-format=ieee, since if
-mabi=ieeelongdouble is specified, it will requires vsx to be enabled.

[Bug target/114402] rs6000: ICE when long double is ieee128 format by default but without vsx

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114402

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |powerpc64*-linux-gnu
           Keywords|                            |ice-on-valid-code
   Target Milestone|---                         |15.0
      Known to fail|                            |12.3.1, 13.2.1

[Bug target/114402] rs6000: ICE when long double is ieee128 format by default but without vsx

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114402

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bergner at gcc dot gnu.org,
                   |                            |gnu@the-meissners.org,
                   |                            |segher at gcc dot gnu.org
   Last reconfirmed|                            |2024-03-21
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |linkw at gcc dot gnu.org

[Bug target/114402] rs6000: ICE when long double is ieee128 format by default but without vsx

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114402

--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
Currently the only pattern to match IEEE128 comparison is:

;; IEEE 128-bit comparisons
(define_insn "*cmp<mode>_hw"
  [(set (match_operand:CCFP 0 "cc_reg_operand" "=y")
        (compare:CCFP (match_operand:IEEE128 1 "altivec_register_operand" "v")
                      (match_operand:IEEE128 2 "altivec_register_operand"
"v")))]
  "TARGET_FLOAT128_HW && FLOAT128_IEEE_P (<MODE>mode)"
   "xscmpuqp %0,%1,%2"
  [(set_attr "type" "veccmp")
   (set_attr "size" "128")])

It requires TARGET_FLOAT128_HW, so nothing can be used for matching.

The below patch can fix this ICE, it makes no-vsx IEEE128 also go with libfunc
call like !TARGET_FLOAT128_HW && FLOAT128_VECTOR_P (mode).

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 5d975dab921..237d138faec 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -15329,7 +15329,7 @@ rs6000_generate_compare (rtx cmp, machine_mode mode)
   rtx op0 = XEXP (cmp, 0);
   rtx op1 = XEXP (cmp, 1);

-  if (!TARGET_FLOAT128_HW && FLOAT128_VECTOR_P (mode))
+  if (!TARGET_FLOAT128_HW && FLOAT128_IEEE_P (mode))
     comp_mode = CCmode;
   else if (FLOAT_MODE_P (mode))
     comp_mode = CCFPmode;
@@ -15361,7 +15361,7 @@ rs6000_generate_compare (rtx cmp, machine_mode mode)

   /* IEEE 128-bit support in VSX registers when we do not have hardware
      support.  */
-  if (!TARGET_FLOAT128_HW && FLOAT128_VECTOR_P (mode))
+  if (!TARGET_FLOAT128_HW && FLOAT128_IEEE_P (mode))
     {
       rtx libfunc = NULL_RTX;
       bool check_nan = false;

[Bug target/114402] rs6000: ICE when long double is ieee128 format by default but without vsx

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114402

--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Kewen Lin <linkw@gcc.gnu.org>:

https://gcc.gnu.org/g:c547e353597ac4e0af09c2faca8c5a16744dcea4

commit r15-702-gc547e353597ac4e0af09c2faca8c5a16744dcea4
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Mon May 20 21:01:06 2024 -0500

    rs6000: Fix ICE on IEEE128 long double without vsx [PR114402]

    As PR114402 shows, we supports IEEE128 format long double
    even if there is no vsx support, but there is an ICE about
    cbranch as the test case shows.  For now, we only supports
    compare:CCFP pattern for IEEE128 fp if TARGET_FLOAT128_HW,
    so in function rs6000_generate_compare we have a check with
    !TARGET_FLOAT128_HW && FLOAT128_VECTOR_P (mode) to make
    !TARGET_FLOAT128_HW IEEE128 fp handling go with libcall.
    But unfortunately the IEEE128 without vsx support doesn't
    meet FLOAT128_VECTOR_P (mode) so it goes further with an
    unmatched compare:CCFP pattern which triggers ICE.

    So this patch is to make rs6000_generate_compare consider
    IEEE128 without vsx as well then it can end up with libcall.

            PR target/114402

    gcc/ChangeLog:

            * config/rs6000/rs6000.cc (rs6000_generate_compare): Make IEEE128
            handling without vsx go with libcall.

    gcc/testsuite/ChangeLog:

            * gcc.target/powerpc/pr114402.c: New test.

[Bug target/114402] rs6000: ICE when long double is ieee128 format by default but without vsx

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114402

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #3 from Kewen Lin <linkw at gcc dot gnu.org> ---
Not a regression, it should be rare to adopt ieee long double but disabling
vsx, so not backported.  Should be fixed on trunk.