fpu: Always decide snan_bit_is_one() at runtime

Currently we have a compile-time shortcut where we return a hardcode
value from snan_bit_is_one() on everything except MIPS, because we
know that's the only target that needs to change
status->no_signaling_nans at runtime.

Remove the ifdef, so we always look at the status flag.  This means
we must update the two targets (HPPA and SH4) that were previously
hardcoded to return true so that they set the status flag correctly.

This has no behavioural change, but will be necessary if we want to
build softfloat once for all targets.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250224111524.1101196-11-peter.maydell@linaro.org
Message-id: 20250217125055.160887-9-peter.maydell@linaro.org

fpu/softfloat-specialize.c.inc

@@ -93,17 +93,10 @@ static inline bool no_signaling_nans(float_status *status)
  * In IEEE 754-1985 this was implementation defined, but in IEEE 754-2008
  * the msb must be zero.  MIPS is (so far) unique in supporting both the
  * 2008 revision and backward compatibility with their original choice.
- * Thus for MIPS we must make the choice at runtime.
  */
 static inline bool snan_bit_is_one(float_status *status)
 {
-#if defined(TARGET_MIPS)
     return status->snan_bit_is_one;
-#elif defined(TARGET_HPPA) || defined(TARGET_SH4)
-    return 1;
-#else
-    return 0;
-#endif
 }
 
 /*----------------------------------------------------------------------------

target/hppa/fpu_helper.c

@@ -67,6 +67,7 @@ void HELPER(loaded_fr0)(CPUHPPAState *env)
     set_float_infzeronan_rule(float_infzeronan_dnan_never, &env->fp_status);
     /* Default NaN: sign bit clear, msb-1 frac bit set */
     set_float_default_nan_pattern(0b00100000, &env->fp_status);
+    set_snan_bit_is_one(true, &env->fp_status);
     /*
      * "PA-RISC 2.0 Architecture" says it is IMPDEF whether the flushing
      * enabled by FPSR.D happens before or after rounding. We pick "before"

target/sh4/cpu.c

@@ -128,6 +128,7 @@ static void superh_cpu_reset_hold(Object *obj, ResetType type)
     set_flush_to_zero(1, &env->fp_status);
 #endif
     set_default_nan_mode(1, &env->fp_status);
+    set_snan_bit_is_one(true, &env->fp_status);
     /* sign bit clear, set all frac bits other than msb */
     set_float_default_nan_pattern(0b00111111, &env->fp_status);
     /*