[Bug target/106574] gcc 12 with O3 leads to failures in glibc's y1f128 tests

["michael.hudson at canonical dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106574

--- Comment #10 from Michael Hudson-Doyle <michael.hudson at canonical dot com> ---
FWIW, I see a similar error on ppc64el with what looks like a similar cause. (I
also see other errors that do not go away with s/O3/O2/ so that might be
something slightly different).

O3:

(kinetic-ppc64el)root@bobonevm3:/build/glibc-9T9BfE/glibc-2.36/build-tree/ppc64el-libc#
./elf/ld64.so.2 --library-path .:./elf:./math  ./math/test-ibm128-y1
testing long double (without inline functions)
Failure: Test: y1_downward (0x2p+0)
Result:
 is:         -1.07032431540937546888370772277496e-01 
-0x1.b667a3914664758b0c44371e580p-4
 should be:  -1.07032431540937546888370772277477e-01 
-0x1.b667a3914664758b0c44371e520p-4
 difference:  1.84889274661174641893373882488153e-32  
0x1.800000000000000000000000000p-106
 ulp       :  12.0000
 max.ulp   :  11.0000
Maximal error of `y1_downward'
 is      : 12 ulp
 accepted: 11 ulp
Failure: Test: y1_upward (0x1.c1bc2ep+0)
Result:
 is:         -2.49838507061808223791568937534715e-01 
-0x1.ffab54c8e53c466a84209c10030p-3
 should be:  -2.49838507061808223791568937534759e-01 
-0x1.ffab54c8e53c466a84209c100a0p-3
 difference:  4.31408307542740831084539059139024e-32  
0x1.c00000000000000000000000000p-105
 ulp       :  14.0000
 max.ulp   :  9.0000
Failure: Test: y1_upward (0x2p+0)
Result:
 is:         -1.07032431540937546888370772277458e-01 
-0x1.b667a3914664758b0c44371e4c0p-4
 should be:  -1.07032431540937546888370772277475e-01 
-0x1.b667a3914664758b0c44371e518p-4
 difference:  1.69481835106076755068926058947474e-32  
0x1.600000000000000000000000000p-106
 ulp       :  11.0000
 max.ulp   :  9.0000
Maximal error of `y1_upward'
 is      : 14 ulp
 accepted: 9 ulp

Test suite completed:
  175 test cases plus 171 tests for exception flags and
    171 tests for errno executed.

O2:

(kinetic-ppc64el)root@bobonevm3:/build/glibc-9T9BfE/glibc-2.36/build-tree/ppc64el-libc#
./elf/ld64.so.2 --library-path .:./elf:./math  ./math/test-ibm128-y1
testing long double (without inline functions)
Failure: Test: y1_upward (0x1.c1bc2ep+0)
Result:
 is:         -2.49838507061808223791568937534728e-01 
-0x1.ffab54c8e53c466a84209c10050p-3
 should be:  -2.49838507061808223791568937534759e-01 
-0x1.ffab54c8e53c466a84209c100a0p-3
 difference:  3.08148791101957736488956470813589e-32  
0x1.400000000000000000000000000p-105
 ulp       :  10.0000
 max.ulp   :  9.0000
Failure: Test: y1_upward (0x2p+0)
Result:
 is:         -1.07032431540937546888370772277458e-01 
-0x1.b667a3914664758b0c44371e4c0p-4
 should be:  -1.07032431540937546888370772277475e-01 
-0x1.b667a3914664758b0c44371e518p-4
 difference:  1.69481835106076755068926058947474e-32  
0x1.600000000000000000000000000p-106
 ulp       :  11.0000
 max.ulp   :  9.0000
Maximal error of `y1_upward'
 is      : 11 ulp
 accepted: 9 ulp

Test suite completed:
  175 test cases plus 171 tests for exception flags and
    171 tests for errno executed.
  3 errors occurred.

(I also see llround errors on ppc64el, no idea what's going on there...)