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value-range: Fix handling of POLY_INT_CST anti-ranges [PR96146]

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The range infrastructure has code to decompose POLY_INT_CST ranges
to worst-case integer bounds.  However, it had the fundamental flaw
(obvious in hindsight) that it applied to anti-ranges too, meaning
that a range 2+2X would end up with a range of ~[2, +INF], i.e.
[-INF, 1].  This patch decays to varying in that case instead.

I'm still a bit uneasy about this.  ISTM that in terms of
generality:

  SSA_NAME => POLY_INT_CST => INTEGER_CST
           => ADDR_EXPR

I.e. an SSA_NAME could store a POLY_INT_CST and a POLY_INT_CST
could store an INTEGER_CST (before canonicalisation).  POLY_INT_CST
is also “as constant as” ADDR_EXPR (well, OK, only some ADDR_EXPRs
are run-time rather than link-time constants, whereas all POLY_INT_CSTs
are, but still).  So it seems like we should at least be able to treat
POLY_INT_CST as symbolic.  On the other hand, I don't have any examples
in which that would be useful.

gcc/
	PR tree-optimization/96146
	* value-range.cc (value_range::set): Only decompose POLY_INT_CST
	bounds to integers for VR_RANGE.  Decay to VR_VARYING for anti-ranges
	involving POLY_INT_CSTs.

gcc/testsuite/
	PR tree-optimization/96146
	* gcc.target/aarch64/sve/acle/general/pr96146.c: New test.
This commit is contained in:
Richard Sandiford 2020-07-11 13:25:26 +01:00
parent c19f95fb1b
commit 505032d97d
2 changed files with 48 additions and 19 deletions
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20
gcc/testsuite/gcc.target/aarch64/sve/acle/general/pr96146.c Normal file
View File

@ -0,0 +1,20 @@
/* { dg-do run { target aarch64_sve_hw } } */
/* { dg-options "-O3" } */
#include <arm_sve.h>
void __attribute__ ((noipa))
f (volatile int *x)
{
int i;
for (int i = 0; i < svcntd (); ++i)
*x = i;
}
int
main (void)
{
volatile int x;
f (&x);
return 0;
}

47
gcc/value-range.cc
View File

@ -86,7 +86,34 @@ value_range::set (tree min, tree max, value_range_kind kind)
set_undefined ();
return;
}
else if (kind == VR_VARYING)
if (kind == VR_RANGE)
{
/* Convert POLY_INT_CST bounds into worst-case INTEGER_CST bounds. */
if (POLY_INT_CST_P (min))
{
tree type_min = vrp_val_min (TREE_TYPE (min));
widest_int lb
= constant_lower_bound_with_limit (wi::to_poly_widest (min),
wi::to_widest (type_min));
min = wide_int_to_tree (TREE_TYPE (min), lb);
}
if (POLY_INT_CST_P (max))
{
tree type_max = vrp_val_max (TREE_TYPE (max));
widest_int ub
= constant_upper_bound_with_limit (wi::to_poly_widest (max),
wi::to_widest (type_max));
max = wide_int_to_tree (TREE_TYPE (max), ub);
}
}
else if (kind != VR_VARYING)
{
if (POLY_INT_CST_P (min) || POLY_INT_CST_P (max))
kind = VR_VARYING;
}
if (kind == VR_VARYING)
{
gcc_assert (TREE_TYPE (min) == TREE_TYPE (max));
tree typ = TREE_TYPE (min);
@ -99,24 +126,6 @@ value_range::set (tree min, tree max, value_range_kind kind)
return;
}
/* Convert POLY_INT_CST bounds into worst-case INTEGER_CST bounds. */
if (POLY_INT_CST_P (min))
{
tree type_min = vrp_val_min (TREE_TYPE (min));
widest_int lb
= constant_lower_bound_with_limit (wi::to_poly_widest (min),
wi::to_widest (type_min));
min = wide_int_to_tree (TREE_TYPE (min), lb);
}
if (POLY_INT_CST_P (max))
{
tree type_max = vrp_val_max (TREE_TYPE (max));
widest_int ub
= constant_upper_bound_with_limit (wi::to_poly_widest (max),
wi::to_widest (type_max));
max = wide_int_to_tree (TREE_TYPE (max), ub);
}
/* Nothing to canonicalize for symbolic ranges. */
if (TREE_CODE (min) != INTEGER_CST
|| TREE_CODE (max) != INTEGER_CST)