[PATCH] expansion: Use __trunchfbf2 calls rather than __extendhfbf2 [PR114907]

[Jakub Jelinek]

Hi!

The HF and BF modes have the same size/precision and neither is
a subset nor superset of the other.
So, using either __extendhfbf2 or __trunchfbf2 is weird.
The expansion apparently emits __extendhfbf2, but on the libgcc side
we apparently have __trunchfbf2 implemented.

I think it is easier to switch to using what is available rather than
adding new entrypoints to libgcc, even alias, because this is backportable.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2024-05-07  Jakub Jelinek  <ja...@redhat.com>

        PR middle-end/114907
        * expr.cc (convert_mode_scalar): Use trunc_optab rather than
        sext_optab for HF->BF conversions.
        * optabs-libfuncs.cc (gen_trunc_conv_libfunc): Likewise.

        * gcc.dg/pr114907.c: New test.

--- gcc/expr.cc.jj      2024-04-09 09:29:04.000000000 +0200
+++ gcc/expr.cc 2024-05-06 13:21:33.933798494 +0200
@@ -355,8 +355,16 @@ convert_mode_scalar (rtx to, rtx from, i
                      && REAL_MODE_FORMAT (from_mode) == &ieee_half_format));
 
       if (GET_MODE_PRECISION (from_mode) == GET_MODE_PRECISION (to_mode))
-       /* Conversion between decimal float and binary float, same size.  */
-       tab = DECIMAL_FLOAT_MODE_P (from_mode) ? trunc_optab : sext_optab;
+       {
+         if (REAL_MODE_FORMAT (to_mode) == &arm_bfloat_half_format
+             && REAL_MODE_FORMAT (from_mode) == &ieee_half_format)
+           /* libgcc implements just __trunchfbf2, not __extendhfbf2.  */
+           tab = trunc_optab;
+         else
+           /* Conversion between decimal float and binary float, same
+              size.  */
+           tab = DECIMAL_FLOAT_MODE_P (from_mode) ? trunc_optab : sext_optab;
+       }
       else if (GET_MODE_PRECISION (from_mode) < GET_MODE_PRECISION (to_mode))
        tab = sext_optab;
       else
--- gcc/optabs-libfuncs.cc.jj   2024-01-03 11:51:31.739728303 +0100
+++ gcc/optabs-libfuncs.cc      2024-05-06 15:50:21.611027802 +0200
@@ -589,7 +589,9 @@ gen_trunc_conv_libfunc (convert_optab ta
   if (GET_MODE_CLASS (float_tmode) != GET_MODE_CLASS (float_fmode))
     gen_interclass_conv_libfunc (tab, opname, float_tmode, float_fmode);
 
-  if (GET_MODE_PRECISION (float_fmode) <= GET_MODE_PRECISION (float_tmode))
+  if (GET_MODE_PRECISION (float_fmode) <= GET_MODE_PRECISION (float_tmode)
+      && (REAL_MODE_FORMAT (float_tmode) != &arm_bfloat_half_format
+         || REAL_MODE_FORMAT (float_fmode) != &ieee_half_format))
     return;
 
   if (GET_MODE_CLASS (float_tmode) == GET_MODE_CLASS (float_fmode))
--- gcc/testsuite/gcc.dg/pr114907.c.jj  2024-05-06 15:59:08.734958523 +0200
+++ gcc/testsuite/gcc.dg/pr114907.c     2024-05-06 16:02:38.914139829 +0200
@@ -0,0 +1,27 @@
+/* PR middle-end/114907 */
+/* { dg-do run } */
+/* { dg-options "" } */
+/* { dg-add-options float16 } */
+/* { dg-require-effective-target float16_runtime } */
+/* { dg-add-options bfloat16 } */
+/* { dg-require-effective-target bfloat16_runtime } */
+
+__attribute__((noipa)) _Float16
+foo (__bf16 x)
+{
+  return (_Float16) x;
+}
+
+__attribute__((noipa)) __bf16
+bar (_Float16 x)
+{
+  return (__bf16) x;
+}
+
+int
+main ()
+{
+  if (foo (11.125bf16) != 11.125f16
+      || bar (11.125f16) != 11.125bf16)
+    __builtin_abort ();
+}

        Jakub