Doh! Wrong patch2.txt file. Sorry.
-----Original Message-----
From: Roger Sayle <[email protected]>
Sent: 27 November 2020 10:52
To: 'Jakub Jelinek' <[email protected]>; 'Joseph S. Myers'
<[email protected]>
Cc: 'Richard Biener' <[email protected]>; '[email protected]'
<[email protected]>
Subject: RE: [PATCH] fold-const: Don't consider NaN non-negative [PR97965]
Hi Jakub,
Technically, PR97965 doesn't explicitly mention equality/inequality, but
you're right, it makes sense to tackle this missed optimization at the same
time as we fix the wrong-code.
On Thu, Nov 26, 2020, Jakub Jelinek wrote:
>On Thu, Nov 26, 2020 at 01:56:03PM -0000, Roger Sayle wrote:
>> --- a/gcc/match.pd
>> +++ b/gcc/match.pd
>> @@ -3998,7 +3998,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>> (cmp @0 { build_real (TREE_TYPE (@1), dconst0); }))
>> /* x != NaN is always true, other ops are always false. */
>> (if (REAL_VALUE_ISNAN (TREE_REAL_CST (@1))
>> - && ! HONOR_SNANS (@1))
>> + && ! flag_trapping_math)
>
>Shouldn't this one stay as is for cmp == EQ_EXPR || cmp == NE_EXPR?
>I mean, == or != only raise exceptions on sNaNs, while other simple
comparisons raise on both sNaNs and qNaNs.
The case to be careful of here is that (x == qNaN) can still raise/trap if x
is a sNaN.
Hence, the full condition should include:
&& (!flag_trapping_math
|| ((cmp == EQ_EXPR || cmp == NE_EXPR)
&& !tree_expr_maybe_signaling_nan_p (@1)
&& !tree_expr_maybe_signaling_nan_p (@0)))
Note: I repeat tree_expr_maybe_signaling_nan_p here for symmetry, though
because we know @1 is a NaN, this could have been written as
!tree_expr_signaling_nan_p (@1).
>> --- a/gcc/simplify-rtx.c
>> +++ b/gcc/simplify-rtx.c
>> @@ -5732,12 +5732,13 @@ simplify_const_relational_operation (enum
rtx_code code,
>> if (REAL_VALUE_ISNAN (*d0) || REAL_VALUE_ISNAN (*d1))
>> switch (code)
>> {
>> + case NE:
>> + return flag_trapping_math ? 0 : const_true_rtx;
>
> And here too (for NE and would need moving EQ later too.
Yep/Agreed. These cases become:
case NE:
if (flag_trapping_math
&& (REAL_VALUE_ISSIGNALING_NAN (*d0)
|| REAL_VALUE_ISSIGANLING_NAN (*d1)))
return 0;
return const_true_rtx;
case EQ:
if (flag_trapping_math
&& (REAL_VALUE_ISSIGNALING_NAN (*d0)
|| REAL_VALUE_ISSIGANLING_NAN (*d1)))
return 0;
return const0_rtx;
A revised patch is attached (which I've confirmed compiles but haven't
regression tested).
Many thanks again.
Roger
--
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 632a241a964..b76e80c02a3 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -12007,8 +12007,8 @@ fold_binary_loc (location_t loc, enum tree_code code,
tree type,
strict_overflow_p = false;
if (code == GE_EXPR
&& (integer_zerop (arg1)
- || (! HONOR_NANS (arg0)
- && real_zerop (arg1)))
+ || (real_zerop (arg1)
+ && !tree_expr_maybe_nan_p (arg0)))
&& tree_expr_nonnegative_warnv_p (arg0, &strict_overflow_p))
{
if (strict_overflow_p)
@@ -12024,7 +12024,10 @@ fold_binary_loc (location_t loc, enum tree_code code,
tree type,
/* Convert ABS_EXPR<x> < 0 to false. */
strict_overflow_p = false;
if (code == LT_EXPR
- && (integer_zerop (arg1) || real_zerop (arg1))
+ && (integer_zerop (arg1)
+ || (real_zerop (arg1)
+ && (!flag_trapping_math
+ || !tree_expr_maybe_nan_p (arg0))))
&& tree_expr_nonnegative_warnv_p (arg0, &strict_overflow_p))
{
if (strict_overflow_p)
diff --git a/gcc/match.pd b/gcc/match.pd
index b6dfc24af88..ef1bfb42d12 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -4037,7 +4037,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(cmp @0 { build_real (TREE_TYPE (@1), dconst0); }))
/* x != NaN is always true, other ops are always false. */
(if (REAL_VALUE_ISNAN (TREE_REAL_CST (@1))
- && ! HONOR_SNANS (@1))
+ && (!flag_trapping_math
+ || ((cmp == EQ_EXPR || cmp == NE_EXPR)
+ && !tree_expr_maybe_signaling_nan_p (@1)
+ && !tree_expr_maybe_signaling_nan_p (@0))))
{ constant_boolean_node (cmp == NE_EXPR, type); })
/* Fold comparisons against infinity. */
(if (REAL_VALUE_ISINF (TREE_REAL_CST (@1))
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 47e7aebda8a..dd97a353bff 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -5732,20 +5732,31 @@ simplify_const_relational_operation (enum rtx_code code,
if (REAL_VALUE_ISNAN (*d0) || REAL_VALUE_ISNAN (*d1))
switch (code)
{
+ case NE:
+ if (flag_trapping_math
+ && (REAL_VALUE_ISSIGNALING_NAN (*d0)
+ || REAL_VALUE_ISSIGNALING_NAN (*d1)))
+ return 0;
+ return const_true_rtx;
case UNEQ:
case UNLT:
case UNGT:
case UNLE:
case UNGE:
- case NE:
case UNORDERED:
return const_true_rtx;
case EQ:
+ if (flag_trapping_math
+ && (REAL_VALUE_ISSIGNALING_NAN (*d0)
+ || REAL_VALUE_ISSIGNALING_NAN (*d1)))
+ return 0;
+ return const0_rtx;
case LT:
case GT:
case LE:
case GE:
case LTGT:
+ return flag_trapping_math ? 0 : const0_rtx;
case ORDERED:
return const0_rtx;
default:
