On Wed, Sep 2, 2015 at 1:36 PM, Sujoy Saraswati <ssarasw...@gmail.com> wrote:
> Hi Richard,
>
>> Note that I'm curious what
>> the actual bug is - is it that (double) sNaN creates a sNaN? Then the fix
>> should be elsewhere, in constant folding itself
>> (fold_convert_const_real_from_real
>> or real_convert).
>>
>> If that isn't the bug you have very many other passes to fix for the
>> same problem.
>>
>> So - can you please explain?
>
> In this test case, the floating point operation for converting the
> float to double is what should convert the sNaN to qNaN. I tried to
> cover more floating point operations than just the conversion
> operations exposed by this test case. For example, if we consider the
> following program -
>
> #define _GNU_SOURCE
> #include <stdio.h>
> #include <math.h>
>
> int main (void)
> {
> float x;
> float sNaN = __builtin_nansf ("");
> x = sNaN + .0;
> return issignaling(x);
> }
>
> The operation (sNaN + .0) should also result in qNaN after folding.
> Hence, I thought of doing the sNaN to qNaN conversion in various
> places under tree-ssa-ccp, where the result upon a folding is
> available. I do agree that this approach may mean many more such
> places should also be covered in other passes, but thought of sending
> the fix for the ccp pass to start with.
>
> Let me know if you suggest alternate approach.
CCP and other passes ultimatively end up using fold-const.c:const_{unop,binop}
for constant folding so that is where the fix should go to (or to real.c). That
will automatically handle other passes doing similar transforms.
Richard.
> Regards,
> Sujoy
>
>> Thanks,
>> Richard.
>>
>>> Regards,
>>> Sujoy
>>>
>>> 2015-09-01 Sujoy Saraswati <ssarasw...@gmail.com>
>>>
>>> PR tree-optimization/61441
>>> * tree-ssa-ccp.c (convert_snan_to_qnan): Convert sNaN to qNaN when
>>> flag_signaling_nans is off.
>>> (ccp_fold_stmt, visit_assignment, visit_cond_stmt): call
>>> convert_snan_to_qnan to convert sNaN to qNaN on constant folding.
>>>
>>> PR tree-optimization/61441
>>> * gcc.dg/pr61441.c: New testcase.
>>>
>>> Index: gcc/tree-ssa-ccp.c
>>> ===================================================================
>>> --- gcc/tree-ssa-ccp.c (revision 226965)
>>> +++ gcc/tree-ssa-ccp.c (working copy)
>>> @@ -560,6 +560,24 @@ value_to_wide_int (ccp_prop_value_t val)
>>> return 0;
>>> }
>>>
>>> +/* Convert sNaN to qNaN when flag_signaling_nans is off */
>>> +
>>> +static void
>>> +convert_snan_to_qnan (tree expr)
>>> +{
>>> + if (expr
>>> + && (TREE_CODE (expr) == REAL_CST)
>>> + && !flag_signaling_nans)
>>> + {
>>> + REAL_VALUE_TYPE *d = TREE_REAL_CST_PTR (expr);
>>> +
>>> + if (HONOR_NANS (TYPE_MODE (TREE_TYPE (expr)))
>>> + && REAL_VALUE_ISNAN (*d)
>>> + && d->signalling)
>>> + d->signalling = 0;
>>> + }
>>> +}
>>> +
>>> /* Return the value for the address expression EXPR based on alignment
>>> information. */
>>>
>>> @@ -2156,6 +2174,7 @@ ccp_fold_stmt (gimple_stmt_iterator *gsi)
>>> if (val.lattice_val != CONSTANT
>>> || val.mask != 0)
>>> return false;
>>> + convert_snan_to_qnan (val.value);
>>>
>>> if (dump_file)
>>> {
>>> @@ -2197,7 +2216,10 @@ ccp_fold_stmt (gimple_stmt_iterator *gsi)
>>> bool res;
>>> if (!useless_type_conversion_p (TREE_TYPE (lhs),
>>> TREE_TYPE (new_rhs)))
>>> + {
>>> new_rhs = fold_convert (TREE_TYPE (lhs), new_rhs);
>>> + convert_snan_to_qnan (new_rhs);
>>> + }
>>> res = update_call_from_tree (gsi, new_rhs);
>>> gcc_assert (res);
>>> return true;
>>> @@ -2216,6 +2238,7 @@ ccp_fold_stmt (gimple_stmt_iterator *gsi)
>>> tree new_rhs = fold_builtin_alloca_with_align (stmt);
>>> if (new_rhs)
>>> {
>>> + convert_snan_to_qnan (new_rhs);
>>> bool res = update_call_from_tree (gsi, new_rhs);
>>> tree var = TREE_OPERAND (TREE_OPERAND (new_rhs, 0),0);
>>> gcc_assert (res);
>>> @@ -2260,7 +2283,10 @@ ccp_fold_stmt (gimple_stmt_iterator *gsi)
>>> {
>>> tree rhs = unshare_expr (val);
>>> if (!useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE
>>> (rhs)))
>>> + {
>>> rhs = fold_build1 (VIEW_CONVERT_EXPR, TREE_TYPE (lhs), rhs);
>>> + convert_snan_to_qnan (rhs);
>>> + }
>>> gimple_assign_set_rhs_from_tree (gsi, rhs);
>>> return true;
>>> }
>>> @@ -2292,6 +2318,7 @@ visit_assignment (gimple stmt, tree *output_p)
>>> /* Evaluate the statement, which could be
>>> either a GIMPLE_ASSIGN or a GIMPLE_CALL. */
>>> val = evaluate_stmt (stmt);
>>> + convert_snan_to_qnan (val.value);
>>>
>>> /* If STMT is an assignment to an SSA_NAME, we only have one
>>> value to set. */
>>> @@ -2324,6 +2351,7 @@ visit_cond_stmt (gimple stmt, edge *taken_edge_p)
>>> if (val.lattice_val != CONSTANT
>>> || val.mask != 0)
>>> return SSA_PROP_VARYING;
>>> + convert_snan_to_qnan (val.value);
>>>
>>> /* Find which edge out of the conditional block will be taken and add it
>>> to the worklist. If no single edge can be determined statically,
>>>
>>> Index: gcc/testsuite/gcc.dg/pr61441.c
>>> ===================================================================
>>> --- gcc/testsuite/gcc.dg/pr61441.c (revision 0)
>>> +++ gcc/testsuite/gcc.dg/pr61441.c (working copy)
>>> @@ -0,0 +1,17 @@
>>> +/* { dg-do run } */
>>> +/* { dg-options "-O1 -lm" } */
>>> +
>>> +#define _GNU_SOURCE
>>> +#include <stdio.h>
>>> +#include <math.h>
>>> +
>>> +int main (void)
>>> +{
>>> + float sNaN = __builtin_nansf ("");
>>> + double x = (double) sNaN;
>>> + if (issignaling(x))
>>> + {
>>> + __builtin_abort();
>>> + }
>>> + return 0;
>>> +}
