On Wed, 27 Oct 2021, Richard Biener wrote:
> On October 27, 2021 4:44:53 PM GMT+02:00, Jakub Jelinek <ja...@redhat.com>
> wrote:
> >On Wed, Oct 27, 2021 at 04:29:38PM +0200, Richard Biener wrote:
> >> So something like the following below? Note I have to fix
> >> simplify_const_unary_operation to not perform the invalid constant
> >> folding with (not worrying about the exact conversion case - I doubt
> >> any of the constant folding is really relevant on RTL these days,
> >> maybe we should simply punt for all unary float-float ops when either
> >> mode has sign dependent rounding modes)
> >>
> >> diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
> >> index bbbd6b74942..9522a31570e 100644
> >> --- a/gcc/simplify-rtx.c
> >> +++ b/gcc/simplify-rtx.c
> >> @@ -2068,6 +2073,9 @@ simplify_const_unary_operation (enum rtx_code code,
> >> machine_mode mode,
> >> and the operand is a signaling NaN. */
> >> if (HONOR_SNANS (mode) && REAL_VALUE_ISSIGNALING_NAN (d))
> >> return NULL_RTX;
> >> + /* Or if flag_rounding_math is on. */
> >> + if (HONOR_SIGN_DEPENDENT_ROUNDING (mode))
> >> + return NULL_RTX;
> >> d = real_value_truncate (mode, d);
> >> break;
> >
> >Won't this stop folding of truncations that are never a problem?
> >I mean at least if the wider float mode constant is exactly representable
> >in the narrower float mode, no matter what rounding mode is used the value
> >will be always the same...
> >And people use
> > float f = 1.0;
> >or
> > float f = 1.25;
> >etc. a lot.
>
> Yes, but I do expect any such opportunities to be realized on GENERIC/GIMPLE?
>
> >So perhaps again
> > if (HONOR_SIGN_DEPENDENT_ROUNDING (mode)
> > && !exact_real_truncate (mode, &d))
> > return NULL_RTX;
> >?
>
> Sure, for this case it's short and straight forward.
>
> >
> >> /* PR57245 */
> >> /* { dg-do run } */
> >> /* { dg-require-effective-target fenv } */
> >> /* { dg-additional-options "-frounding-math" } */
> >>
> >> #include <fenv.h>
> >> #include <stdlib.h>
> >>
> >> int
> >> main ()
> >> {
> >
> >Roughly yes. Some tests also do #ifdef FE_*, so in your case
> >> #if __DBL_MANT_DIG__ == 53 && __FLT_MANT_DIG__ == 24
> >+#ifdef FE_UPWARD
>
> Ah, OK. Will fix.
So like this - bootstrapped and tested on x86_64-unknown-linux-gnu.
OK now?
Thanks,
Richard.
>From 22da541c70ec2eff1e9208dd53c6d7309c33b0c9 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguent...@suse.de>
Date: Wed, 27 Oct 2021 14:27:40 +0200
Subject: [PATCH] middle-end/57245 - honor -frounding-math in real truncation
To: gcc-patches@gcc.gnu.org
The following honors -frounding-math when converting a FP constant
to another FP type.
2021-10-27 Richard Biener <rguent...@suse.de>
PR middle-end/57245
* fold-const.c (fold_convert_const_real_from_real): Honor
-frounding-math if the conversion is not exact.
* simplify-rtx.c (simplify_const_unary_operation): Do not
simplify FLOAT_TRUNCATE with sign dependent rounding.
* gcc.dg/torture/fp-double-convert-float-1.c: New testcase.
---
gcc/fold-const.c | 6 +++
gcc/simplify-rtx.c | 5 +++
.../torture/fp-double-convert-float-1.c | 41 +++++++++++++++++++
3 files changed, 52 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/torture/fp-double-convert-float-1.c
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index ff23f12f33c..18950aeb760 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -2139,6 +2139,12 @@ fold_convert_const_real_from_real (tree type, const_tree
arg1)
&& REAL_VALUE_ISSIGNALING_NAN (TREE_REAL_CST (arg1)))
return NULL_TREE;
+ /* With flag_rounding_math we should respect the current rounding mode
+ unless the conversion is exact. */
+ if (HONOR_SIGN_DEPENDENT_ROUNDING (arg1)
+ && !exact_real_truncate (TYPE_MODE (type), &TREE_REAL_CST (arg1)))
+ return NULL_TREE;
+
real_convert (&value, TYPE_MODE (type), &TREE_REAL_CST (arg1));
t = build_real (type, value);
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index bbbd6b74942..f38b6d7d31c 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -2068,6 +2068,11 @@ simplify_const_unary_operation (enum rtx_code code,
machine_mode mode,
and the operand is a signaling NaN. */
if (HONOR_SNANS (mode) && REAL_VALUE_ISSIGNALING_NAN (d))
return NULL_RTX;
+ /* Or if flag_rounding_math is on and the truncation is not
+ exact. */
+ if (HONOR_SIGN_DEPENDENT_ROUNDING (mode)
+ && !exact_real_truncate (mode, &d))
+ return NULL_RTX;
d = real_value_truncate (mode, d);
break;
case FLOAT_EXTEND:
diff --git a/gcc/testsuite/gcc.dg/torture/fp-double-convert-float-1.c
b/gcc/testsuite/gcc.dg/torture/fp-double-convert-float-1.c
new file mode 100644
index 00000000000..ec23274ea98
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/fp-double-convert-float-1.c
@@ -0,0 +1,41 @@
+/* PR57245 */
+/* { dg-do run } */
+/* { dg-require-effective-target fenv } */
+/* { dg-additional-options "-frounding-math" } */
+
+#include <fenv.h>
+#include <stdlib.h>
+
+int
+main ()
+{
+#if __DBL_MANT_DIG__ == 53 && __FLT_MANT_DIG__ == 24
+#ifdef FE_UPWARD
+ fesetround (FE_UPWARD);
+ float f = 1.3;
+ if (f != 0x1.4ccccep+0f)
+ __builtin_abort ();
+#endif
+#ifdef FE_TONEAREST
+ fesetround (FE_TONEAREST);
+ /* Use different actual values so the bogus CSE we perform does not
+ break things. */
+ f = 1.33;
+ if (f != 0x1.547ae2p+0f)
+ abort ();
+#endif
+#ifdef FE_DOWNWARD
+ fesetround (FE_DOWNWARD);
+ f = 1.333;
+ if (f != 0x1.553f7cp+0f)
+ abort ();
+#endif
+#ifdef FE_TOWARDZERO
+ fesetround (FE_TOWARDZERO);
+ f = 1.3333;
+ if (f != 0x1.555326p+0f)
+ abort ();
+#endif
+#endif
+ return 0;
+}
--
2.31.1
