Re: [PATCH] Builtin function roundeven folding implementation

[Tejas Joshi <tejasjoshi9673 at gmail dot com>]

Hi.
Here is a clean patch that does not fold roundeven resulting for
integer type and the conditions for folding functions
round/ceil/floor/roundeven and trunc only checks for signaling NaN.
This patch also conforms to GNU's coding style and standards. The fact
that it should be CASE_MATHFN_FLOATN rather than CASE_MATHFN for
roundeven is corrected in i386 expansion patch.

Thanks,
Tejas

gcc/ChangeLog:

2019-06-12  Tejas Joshi  <tejasjoshi9673@gmail.com>

    * builtins.c (mathfn_built_in_2): Added CASE_MATHFN for ROUNDEVEN.
    * builtins.def: Added function definitions for roundeven function
    variants.
    * fold-const-call.c (fold_const_call_ss): Added case for roundeven
    function call.
    * fold-const.c (negate_mathfn_p): Added case for roundeven function.
    (tree_call_nonnegative_warnv_p): Added case for roundeven function.
    (integer_valued_real_call_p): Added case for roundeven function.
    * real.c (is_even): New function. Returns true if real number is
    even, otherwise returns false.
    (is_halfway_below): New function. Returns true if real number is
    halfway between two integers, else return false.
    (real_roundeven): New function. Round real number to nearest
    integer, rounding halfway cases towards even.
    * real.h (real_value): Added descriptive comments.
    Added function declaration for roundeven function.

gcc/testsuite/ChangeLog:

2019-06-12  Tejas Joshi  <tejasjoshi9673@gmail.com>

    * gcc.dg/torture/builtin-round-roundeven.c: New test.
    * gcc.dg/torture/builtin-round-roundevenf128.c: New test.

On Sat, 10 Aug 2019 at 02:15, Joseph Myers <joseph@codesourcery.com> wrote:
>
> On Fri, 28 Jun 2019, Tejas Joshi wrote:
>
> > +    CASE_CFN_ROUNDEVEN:
> > +    CASE_CFN_ROUNDEVEN_FN:
> > +      if (!REAL_VALUE_ISNAN (*arg) || !flag_errno_math)
>
> Checking flag_errno_math here does not make sense.  roundeven never sets
> errno (at least, TS 18661-1 makes it implementation-defined whether sNaN
> input counts as a domain error, but I'm not aware of implementations that
> make it a domain error and set errno, and typically GCC follows glibc in
> such cases in the absence of known implementations requiring a different
> approach).
>
> The only case where you need to avoid folding is where the argument is a
> signaling NaN (it's fine to fold for quiet NaNs).  In that case, you need
> to avoid folding to avoid losing an exception (if the user cares about
> signaling NaNs, they probably care about exceptions) - so it still doesn't
> matter whether the library implementation also sets errno or not.
>
> (Yes, this means the existing ceil / floor / round checks should be
> adjusted just to check for signaling NaN, though that's fairly cosmetic as
> calls to those functions with quiet NaN argument still get folded via
> match.pd.  trunc ought also check for signaling NaN rather than folding
> unconditionally, so all those functions should end up with the same
> conditions for folding.)
>
> > @@ -898,6 +907,10 @@ fold_const_call_ss (wide_int *result, combined_fn fn,
> >        return fold_const_conversion (result, real_round, arg,
> >                                   precision, format);
> >
> > +    CASE_CFN_ROUNDEVEN:
> > +    CASE_CFN_ROUNDEVEN_FN:
> > +      return fold_const_conversion (result, real_roundeven, arg, precision, format);
> > +
>
> This is the version of fold_const_call_ss for functions returning a result
> of integer type; roundeven returns an integer value in a floating-point
> type.  I don't think this code should be there, and I don't think this
> version of the function should be called at all for roundeven.
>
> --
> Joseph S. Myers
> joseph@codesourcery.com

diff --git a/gcc/builtins.c b/gcc/builtins.c
index e2ba356c0d3..8ceb077b0bf 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -2056,6 +2056,7 @@ mathfn_built_in_2 (tree type, combined_fn fn)
     CASE_MATHFN (REMQUO)
     CASE_MATHFN_FLOATN (RINT)
     CASE_MATHFN_FLOATN (ROUND)
+    CASE_MATHFN (ROUNDEVEN)
     CASE_MATHFN (SCALB)
     CASE_MATHFN (SCALBLN)
     CASE_MATHFN (SCALBN)
diff --git a/gcc/builtins.def b/gcc/builtins.def
index 6d41bdb4f44..8bb7027aac7 100644
--- a/gcc/builtins.def
+++ b/gcc/builtins.def
@@ -542,12 +542,18 @@ DEF_C99_BUILTIN        (BUILT_IN_RINTL, "rintl", BT_FN_LONGDOUBLE_LONGDOUBLE, AT
 #define RINT_TYPE(F) BT_FN_##F##_##F
 DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_RINT, "rint", RINT_TYPE, ATTR_CONST_NOTHROW_LEAF_LIST)
 #undef RINT_TYPE
+DEF_EXT_LIB_BUILTIN    (BUILT_IN_ROUNDEVEN, "roundeven", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
+DEF_EXT_LIB_BUILTIN    (BUILT_IN_ROUNDEVENF, "roundevenf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
+DEF_EXT_LIB_BUILTIN    (BUILT_IN_ROUNDEVENL, "roundevenl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUND, "round", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUNDF, "roundf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUNDL, "roundl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 #define ROUND_TYPE(F) BT_FN_##F##_##F
 DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_ROUND, "round", ROUND_TYPE, ATTR_CONST_NOTHROW_LEAF_LIST)
 #undef ROUND_TYPE
+#define ROUNDEVEN_TYPE(F) BT_FN_##F##_##F
+DEF_EXT_LIB_FLOATN_NX_BUILTINS (BUILT_IN_ROUNDEVEN, "roundeven", ROUNDEVEN_TYPE, ATTR_CONST_NOTHROW_LEAF_LIST)
+#undef ROUNDEVEN_TYPE
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_SCALB, "scalb", BT_FN_DOUBLE_DOUBLE_DOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_SCALBF, "scalbf", BT_FN_FLOAT_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
 DEF_EXT_LIB_BUILTIN    (BUILT_IN_SCALBL, "scalbl", BT_FN_LONGDOUBLE_LONGDOUBLE_LONGDOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
diff --git a/gcc/fold-const-call.c b/gcc/fold-const-call.c
index 702c8b4057a..73dfb6980f1 100644
--- a/gcc/fold-const-call.c
+++ b/gcc/fold-const-call.c
@@ -806,7 +806,7 @@ fold_const_call_ss (real_value *result, combined_fn fn,
 
     CASE_CFN_FLOOR:
     CASE_CFN_FLOOR_FN:
-      if (!REAL_VALUE_ISNAN (*arg) || !flag_errno_math)
+      if (!REAL_VALUE_ISNAN (*arg))
 	{
 	  real_floor (result, format, arg);
 	  return true;
@@ -815,7 +815,7 @@ fold_const_call_ss (real_value *result, combined_fn fn,
 
     CASE_CFN_CEIL:
     CASE_CFN_CEIL_FN:
-      if (!REAL_VALUE_ISNAN (*arg) || !flag_errno_math)
+      if (!REAL_VALUE_ISNAN (*arg))
 	{
 	  real_ceil (result, format, arg);
 	  return true;
@@ -824,18 +824,31 @@ fold_const_call_ss (real_value *result, combined_fn fn,
 
     CASE_CFN_TRUNC:
     CASE_CFN_TRUNC_FN:
-      real_trunc (result, format, arg);
-      return true;
+      if (!REAL_VALUE_ISNAN (*arg))
+	{
+	  real_trunc (result, format, arg);
+	  return true;
+	}
+      return false;
 
     CASE_CFN_ROUND:
     CASE_CFN_ROUND_FN:
-      if (!REAL_VALUE_ISNAN (*arg) || !flag_errno_math)
+      if (!REAL_VALUE_ISNAN (*arg))
 	{
 	  real_round (result, format, arg);
 	  return true;
 	}
       return false;
 
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
+      if (!REAL_VALUE_ISNAN (*arg))
+	{
+	  real_roundeven (result, format, arg);
+	  return true;
+	}
+      return false;
+
     CASE_CFN_LOGB:
       return fold_const_logb (result, arg, format);
 
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 0ca472d422f..07d82a17e25 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -329,6 +329,8 @@ negate_mathfn_p (combined_fn fn)
     CASE_CFN_LLROUND:
     CASE_CFN_LROUND:
     CASE_CFN_ROUND:
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
     CASE_CFN_SIN:
     CASE_CFN_SINH:
     CASE_CFN_TAN:
@@ -13063,6 +13065,8 @@ tree_call_nonnegative_warnv_p (tree type, combined_fn fn, tree arg0, tree arg1,
     CASE_CFN_RINT_FN:
     CASE_CFN_ROUND:
     CASE_CFN_ROUND_FN:
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
     CASE_CFN_SCALB:
     CASE_CFN_SCALBLN:
     CASE_CFN_SCALBN:
@@ -13586,6 +13590,8 @@ integer_valued_real_call_p (combined_fn fn, tree arg0, tree arg1, int depth)
     CASE_CFN_RINT_FN:
     CASE_CFN_ROUND:
     CASE_CFN_ROUND_FN:
+    CASE_CFN_ROUNDEVEN:
+    CASE_CFN_ROUNDEVEN_FN:
     CASE_CFN_TRUNC:
     CASE_CFN_TRUNC_FN:
       return true;
diff --git a/gcc/real.c b/gcc/real.c
index 0164f097a53..0c0d8c51fe4 100644
--- a/gcc/real.c
+++ b/gcc/real.c
@@ -5010,6 +5010,89 @@ real_round (REAL_VALUE_TYPE *r, format_helper fmt,
     real_convert (r, fmt, r);
 }
 
+/* Return true including 0 if integer part of R is even, else return
+   false.  The function is not valid for rvc_inf and rvc_nan classes.  */
+
+bool
+is_even (REAL_VALUE_TYPE *r)
+{
+  gcc_assert (r->cl != rvc_inf);
+  gcc_assert (r->cl != rvc_nan);
+
+  if (r->cl == rvc_zero)
+    return true;
+
+  /* For (-1,1), number is even.  */
+  if (REAL_EXP (r) <= 0)
+    return true;
+
+  /* Check lowest bit, if not set, return true.  */
+  else if (REAL_EXP (r) <= SIGNIFICAND_BITS)
+  {
+    unsigned int n = SIGNIFICAND_BITS - REAL_EXP (r);
+    int w = n / HOST_BITS_PER_LONG;
+
+    unsigned long num = ((unsigned long)1 << (n % HOST_BITS_PER_LONG));
+
+    if ((r->sig[w] & num) == 0)
+      return true;
+  }
+
+  else
+    return true;
+
+  return false;
+}
+
+/* Return true if R is halfway between two integers, else return
+   false.  The function is not valid for rvc_inf and rvc_nan classes.  */
+
+bool
+is_halfway_below (const REAL_VALUE_TYPE *r)
+{
+  gcc_assert (r->cl != rvc_inf);
+  gcc_assert (r->cl != rvc_nan);
+  int i;
+
+  /* For numbers (-0.5,0) and (0,0.5).  */
+  if (REAL_EXP (r) < 0)
+    return false;
+
+  else if (REAL_EXP (r) < SIGNIFICAND_BITS)
+  {
+    unsigned int n = SIGNIFICAND_BITS - REAL_EXP (r) - 1;
+    int w = n / HOST_BITS_PER_LONG;
+
+    for (i = 0; i < w; ++i)
+      if (r->sig[i] != 0)
+	return false;
+
+    unsigned long num = ((unsigned long)1 << (n % HOST_BITS_PER_LONG));
+
+    if (((r->sig[w] & num) != 0) && ((r->sig[w] & (num-1)) == 0))
+      return true;
+  }
+  return false;
+}
+
+/* Round X to nearest integer, rounding halfway cases towards even.  */
+
+void
+real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
+		const REAL_VALUE_TYPE *x)
+{
+  if (is_halfway_below (x))
+  {
+    do_add (r, x, &dconsthalf, x->sign);
+    if (!is_even (r))
+      do_add (r, r, &dconstm1, x->sign);
+    if (fmt)
+      real_convert (r, fmt, r);
+  }
+  else
+    real_round (r, fmt, x);
+}
+
 /* Set the sign of R to the sign of X.  */
 
 void
diff --git a/gcc/real.h b/gcc/real.h
index 95b9db83d24..2f41834ecfd 100644
--- a/gcc/real.h
+++ b/gcc/real.h
@@ -41,11 +41,18 @@ struct GTY(()) real_value {
      sure they're packed together, otherwise REAL_VALUE_TYPE_SIZE will
      be miscomputed.  */
   unsigned int /* ENUM_BITFIELD (real_value_class) */ cl : 2;
+  /* 1 if number is decimal floating point.  */
   unsigned int decimal : 1;
+  /* 1 if number is negative.  */
   unsigned int sign : 1;
+  /* 1 if number is signalling.  */
   unsigned int signalling : 1;
+  /* 1 if number is canonical
+  All are generally used for handling cases in real.c.  */
   unsigned int canonical : 1;
+  /* unbiased exponent of the number.  */
   unsigned int uexp : EXP_BITS;
+  /* significand of the number.  */
   unsigned long sig[SIGSZ];
 };
 
@@ -500,6 +507,8 @@ extern void real_ceil (REAL_VALUE_TYPE *, format_helper,
 		       const REAL_VALUE_TYPE *);
 extern void real_round (REAL_VALUE_TYPE *, format_helper,
 			const REAL_VALUE_TYPE *);
+extern void real_roundeven (REAL_VALUE_TYPE *, format_helper,
+			    const REAL_VALUE_TYPE *);
 
 /* Set the sign of R to the sign of X.  */
 extern void real_copysign (REAL_VALUE_TYPE *, const REAL_VALUE_TYPE *);
diff --git a/gcc/testsuite/gcc.dg/torture/builtin-round-roundeven.c b/gcc/testsuite/gcc.dg/torture/builtin-round-roundeven.c
new file mode 100644
index 00000000000..f75adf6ec8a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/builtin-round-roundeven.c
@@ -0,0 +1,23 @@
+/* { dg-do link } */
+
+extern int link_error (int);
+
+#define TEST(FN, VALUE, RESULT) \
+  if (__builtin_##FN (VALUE) != RESULT) link_error (__LINE__);
+
+int
+main (void)
+{
+  TEST(roundeven,  0, 0);
+  TEST(roundeven,  0.5, 0);
+  TEST(roundeven,  -0.5, 0);
+  TEST(roundeven,  6, 6);
+  TEST(roundeven,  -8, -8);
+  TEST(roundeven,  2.5, 2);
+  TEST(roundeven,  3.5, 4);
+  TEST(roundeven,  -1.5, -2);
+  TEST(roundeven,  3.499, 3);
+  TEST(roundeven,  3.501, 4);
+
+  return 0;
+}
\ No newline at end of file
diff --git a/gcc/testsuite/gcc.dg/torture/builtin-round-roundevenf128.c b/gcc/testsuite/gcc.dg/torture/builtin-round-roundevenf128.c
new file mode 100644
index 00000000000..592bad49623
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/builtin-round-roundevenf128.c
@@ -0,0 +1,20 @@
+/* { dg-do link } */
+/* { dg-add-options float128 } */
+/* { dg-require-effective-target float128 } */
+
+extern int link_error (int);
+
+#define TEST(FN, VALUE, RESULT) \
+  if (__builtin_##FN##f128 (VALUE) != RESULT) link_error (__LINE__);
+
+int
+main (void)
+{
+  TEST(roundeven,  (0x1p64+0.5f128), (0x1p64f128));
+  TEST(roundeven,  (0x1p63+0.5f128), (0x1p63f128));
+  TEST(roundeven,  (0x1p63-0.5f128), (0x1p63f128));
+  TEST(roundeven,  (0x1p64-0.5f128), (0x1p64f128));
+  TEST(roundeven,  (0x1p64+0.501f128), (0x1p64+1.0f128));
+  TEST(roundeven,  (0x1.C00000000000039A5653p1f128), (0x1p2f128))
+  return 0;
+}
\ No newline at end of file