[gcc r14-6421] aarch64: Fix wrong code for bfloat when f16 is enabled [PR 111867]

[Andrew Pinski]

https://gcc.gnu.org/g:35ade856eaafd9c39ce864b25d127e1f98a3bb57

commit r14-6421-g35ade856eaafd9c39ce864b25d127e1f98a3bb57
Author: Andrew Pinski <quic_apinski@quicinc.com>
Date:   Sat Dec 9 20:02:24 2023 -0800

    aarch64: Fix wrong code for bfloat when f16 is enabled [PR 111867]
    
    The problem here is when f16 is enabled, movbf_aarch64 accepts `Ufc`
    as a constraint:
         [ w        , Ufc ; fconsts     , fp16  ] fmov\t%h0, %1
    But that is for fmov values and in this case fmov represents f16 rather than bfloat16 values.
    This means we would get the wrong value in the register.
    
    Built and tested for aarch64-linux-gnu with no regressions.  Also tested with `-march=armv9-a+sve2,
    gcc.dg/torture/bfloat16-basic.c and gcc.dg/torture/bfloat16-builtin.c no longer fail.
    
    gcc/ChangeLog:
    
            PR target/111867
            * config/aarch64/aarch64.cc (aarch64_float_const_representable_p): For BFmode,
            only accept +0.0.
    
    Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

Diff:
---
 gcc/config/aarch64/aarch64.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index a58b02d8421..21a24d92b02 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -23936,6 +23936,10 @@ aarch64_float_const_representable_p (rtx x)
       || REAL_VALUE_MINUS_ZERO (r))
     return false;
 
+  /* For BFmode, only handle 0.0. */
+  if (GET_MODE (x) == BFmode)
+    return real_iszero (&r, false);
+
   /* Extract exponent.  */
   r = real_value_abs (&r);
   exponent = REAL_EXP (&r);