[v2,for-10.0,02/54] fpu: Check for default_nan_mode before calling pickNaNMulAdd

Commit Message

Peter Maydell Dec. 2, 2024, 1:12 p.m. UTC

If the target sets default_nan_mode then we're always going to return
the default NaN, and pickNaNMulAdd() no longer has any side effects.
For consistency with pickNaN(), check for default_nan_mode before
calling pickNaNMulAdd().

When we convert pickNaNMulAdd() to allow runtime selection of the NaN
propagation rule, this means we won't have to make the targets which
use default_nan_mode also set a propagation rule.

Since RiscV always uses default_nan_mode, this allows us to remove
its ifdef case from pickNaNMulAdd().

Signed-off-by: Peter Maydell <[e-mail]>
Reviewed-by: Richard Henderson <[e-mail]>
---
 fpu/softfloat-parts.c.inc      | 8 ++++++--
 fpu/softfloat-specialize.c.inc | 9 +++++++--
 2 files changed, 13 insertions(+), 4 deletions(-)

Patch

diff --git a/fpu/softfloat-parts.c.inc b/fpu/softfloat-parts.c.inc
index d63cd957a19..aac1f9cd28c 100644
--- a/fpu/softfloat-parts.c.inc
+++ b/fpu/softfloat-parts.c.inc
@@ -77,9 +77,13 @@  static FloatPartsN *partsN(pick_nan_muladd)(FloatPartsN *a, FloatPartsN *b,
         float_raise(float_flag_invalid | float_flag_invalid_imz, s);
     }
 
-    which = pickNaNMulAdd(a->cls, b->cls, c->cls, infzero, s);
+    if (s->default_nan_mode) {
+        which = 3;
+    } else {
+        which = pickNaNMulAdd(a->cls, b->cls, c->cls, infzero, s);
+    }
 
-    if (s->default_nan_mode || which == 3) {
+    if (which == 3) {
         parts_default_nan(a, s);
         return a;
     }
diff --git a/fpu/softfloat-specialize.c.inc b/fpu/softfloat-specialize.c.inc
index c557c41b2af..81a67eb67b5 100644
--- a/fpu/softfloat-specialize.c.inc
+++ b/fpu/softfloat-specialize.c.inc
@@ -475,6 +475,13 @@  static int pickNaN(FloatClass a_cls, FloatClass b_cls,
 static int pickNaNMulAdd(FloatClass a_cls, FloatClass b_cls, FloatClass c_cls,
                          bool infzero, float_status *status)
 {
+    /*
+     * We guarantee not to require the target to tell us how to
+     * pick a NaN if we're always returning the default NaN.
+     * But if we're not in default-NaN mode then the target must
+     * specify.
+     */
+    assert(!status->default_nan_mode);
 #if defined(TARGET_ARM)
     /* For ARM, the (inf,zero,qnan) case sets InvalidOp and returns
      * the default NaN
@@ -578,8 +585,6 @@  static int pickNaNMulAdd(FloatClass a_cls, FloatClass b_cls, FloatClass c_cls,
     } else {
         return 1;
     }
-#elif defined(TARGET_RISCV)
-    return 3; /* default NaN */
 #elif defined(TARGET_S390X)
     if (infzero) {
         return 3;