* Re: [PATCH] Decimal floats can never be an frange::singleton_p.
2022-09-05 13:47 [PATCH] Decimal floats can never be an frange::singleton_p Aldy Hernandez
@ 2022-09-05 13:51 ` Jakub Jelinek
2022-09-05 15:55 ` Aldy Hernandez
1 sibling, 0 replies; 3+ messages in thread
From: Jakub Jelinek @ 2022-09-05 13:51 UTC (permalink / raw)
To: Aldy Hernandez; +Cc: GCC patches, Andrew MacLeod
On Mon, Sep 05, 2022 at 03:47:01PM +0200, Aldy Hernandez wrote:
> As Jakub mentioned in the PR, because many numbers have multiple
> possible representations, we can't reliably return true here.
>
> I'll commit this if tests pass.
>
> I wonder if its worth even handling decimal floats in frange, since
> there's a lot of things we can't represent. I suppose even though we
> could never propagate an actual value with VRP, we could fold
> conditionals (symbolic and stuff outside ranges, etc) ??.
>
> Thoughts?
>
> PR middle-end/106831
>
> gcc/ChangeLog:
>
> * value-range.cc (frange::singleton_p): Return false for
> DECIMAL_FLOAT_TYPE_P.
> ---
> gcc/value-range.cc | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
> index c3f668a811a..12a3750d078 100644
> --- a/gcc/value-range.cc
> +++ b/gcc/value-range.cc
> @@ -647,6 +647,14 @@ frange::singleton_p (tree *result) const
> if (HONOR_NANS (m_type) && !get_nan ().no_p ())
> return false;
>
> + // Because the significand is not normalized (there is no
> + // implicit leading "1"). Most values with less than 7
> + // significant digits have multiple possible representations.
> + // Zero has 192 possible representations (or twice that for
> + // signed zeros).
The exact details (7, 192) are dependent on the format, for
decimal64 it is (16, 768) and for decimal128 (34, 12288).
Jakub
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Decimal floats can never be an frange::singleton_p.
2022-09-05 13:47 [PATCH] Decimal floats can never be an frange::singleton_p Aldy Hernandez
2022-09-05 13:51 ` Jakub Jelinek
@ 2022-09-05 15:55 ` Aldy Hernandez
1 sibling, 0 replies; 3+ messages in thread
From: Aldy Hernandez @ 2022-09-05 15:55 UTC (permalink / raw)
To: GCC patches; +Cc: Jakub Jelinek, Andrew MacLeod
[-- Attachment #1: Type: text/plain, Size: 1697 bytes --]
Final version of the patch. Disable frange for DECIMAL_FLOAT_MODE_P altogether.
Tested on x86-64 Linux with regstrap as well as mpfr tests.
On Mon, Sep 5, 2022 at 3:47 PM Aldy Hernandez <aldyh@redhat.com> wrote:
>
> As Jakub mentioned in the PR, because many numbers have multiple
> possible representations, we can't reliably return true here.
>
> I'll commit this if tests pass.
>
> I wonder if its worth even handling decimal floats in frange, since
> there's a lot of things we can't represent. I suppose even though we
> could never propagate an actual value with VRP, we could fold
> conditionals (symbolic and stuff outside ranges, etc) ??.
>
> Thoughts?
>
> PR middle-end/106831
>
> gcc/ChangeLog:
>
> * value-range.cc (frange::singleton_p): Return false for
> DECIMAL_FLOAT_TYPE_P.
> ---
> gcc/value-range.cc | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
> index c3f668a811a..12a3750d078 100644
> --- a/gcc/value-range.cc
> +++ b/gcc/value-range.cc
> @@ -647,6 +647,14 @@ frange::singleton_p (tree *result) const
> if (HONOR_NANS (m_type) && !get_nan ().no_p ())
> return false;
>
> + // Because the significand is not normalized (there is no
> + // implicit leading "1"). Most values with less than 7
> + // significant digits have multiple possible representations.
> + // Zero has 192 possible representations (or twice that for
> + // signed zeros).
> + if (DECIMAL_FLOAT_TYPE_P (m_type))
> + return false;
> +
> // Return the appropriate zero if known.
> if (HONOR_SIGNED_ZEROS (m_type) && zero_p ())
> {
> --
> 2.37.1
>
[-- Attachment #2: 0002-Disable-decimal-floating-point-in-frange.patch --]
[-- Type: text/x-patch, Size: 2458 bytes --]
From 4f32e08f7317c52ed72ee48447cb4dd5d68a5c28 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Mon, 5 Sep 2022 15:41:39 +0200
Subject: [PATCH] Disable decimal floating point in frange.
As Jakub mentioned in the PR, because many numbers have multiple
possible representations, we can't reliably return true for singleton_p.
For that matter, we may not be capable of modeling them just yet.
Disabling them until someone with DFP knowledge can opine or extend
frange.
PR middle-end/106831
gcc/ChangeLog:
* value-range.h (frange::supports_p): Disable decimal floats.
* range-op-float.cc (frange_drop_inf): Remove DECIMAL_FLOAT_MODE_P
check.
(frange_drop_ninf): Same.
---
gcc/range-op-float.cc | 10 ----------
gcc/value-range.h | 5 ++++-
2 files changed, 4 insertions(+), 11 deletions(-)
diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 7301e5a060b..050f07a9867 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -204,11 +204,6 @@ frelop_early_resolve (irange &r, tree type,
static inline void
frange_drop_inf (frange &r, tree type)
{
- // FIXME: build_real() bails on decimal float modes when called with
- // a max representable endpoint.
- if (DECIMAL_FLOAT_MODE_P (TYPE_MODE (type)))
- return;
-
REAL_VALUE_TYPE max;
real_max_representable (&max, type);
frange tmp (type, r.lower_bound (), max);
@@ -221,11 +216,6 @@ frange_drop_inf (frange &r, tree type)
static inline void
frange_drop_ninf (frange &r, tree type)
{
- // FIXME: build_real() bails on decimal float modes when called with
- // a max representable endpoint.
- if (DECIMAL_FLOAT_MODE_P (TYPE_MODE (type)))
- return;
-
REAL_VALUE_TYPE min;
real_min_representable (&min, type);
frange tmp (type, min, r.upper_bound ());
diff --git a/gcc/value-range.h b/gcc/value-range.h
index bc00f3d5b08..645dc76c33a 100644
--- a/gcc/value-range.h
+++ b/gcc/value-range.h
@@ -338,7 +338,10 @@ public:
value_range_kind = VR_RANGE);
static bool supports_p (const_tree type)
{
- return SCALAR_FLOAT_TYPE_P (type);
+ // ?? Decimal floats can have multiple representations for the
+ // same number. Supporting them may be as simple as just
+ // disabling them in singleton_p. No clue.
+ return SCALAR_FLOAT_TYPE_P (type) && !DECIMAL_FLOAT_TYPE_P (type);
}
virtual tree type () const override;
virtual void set (tree, tree, value_range_kind = VR_RANGE) override;
--
2.37.1
^ permalink raw reply [flat|nested] 3+ messages in thread