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tree-optimization/105517 - avoid offset truncation during VN

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When value-numbering an address expression like
&p_74(D)->a1x[4294967295].a1; we are accumulating the byte offset
in an 64bit integer.  When later exploiting the duality between
that and a POINTER_PLUS_EXPR we should avoid truncating that
offset to fit in the target specific sizetype.  While such
overflows are generally undefined behavior, exploiting this
may leads to spurious missing diagnostics.

2022-05-09  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/105517
	* tree-ssa-sccvn.cc (vn_reference_lookup): Make sure the accumulated
	offset can be represented in the POINTER_PLUS_EXPR IL.
	(vn_reference_insert): Likewise.
	* poly-int.h (sext_hwi): Add poly version of sext_hwi.
This commit is contained in:
Richard Biener 2022-05-09 11:33:44 +02:00
parent 93416de0cb
commit faabc751d0
2 changed files with 25 additions and 2 deletions
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13
gcc/poly-int.h
View file

@ -1178,6 +1178,19 @@ lshift (const poly_int_pod<N, Ca> &a, const Cb &b)
}
}
/* Poly version of sext_hwi, with the same interface. */
template<unsigned int N, typename C>
inline poly_int<N, HOST_WIDE_INT>
sext_hwi (const poly_int<N, C> &a, unsigned int precision)
{
poly_int_pod<N, HOST_WIDE_INT> r;
for (unsigned int i = 0; i < N; i++)
r.coeffs[i] = sext_hwi (a.coeffs[i], precision);
return r;
}
/* Return true if a0 + a1 * x might equal b0 + b1 * x for some nonnegative
integer x. */

14
gcc/tree-ssa-sccvn.cc
View file

@ -3684,7 +3684,12 @@ vn_reference_lookup (tree op, tree vuse, vn_lookup_kind kind,
break;
off += vro->off;
}
if (i == operands.length () - 1)
if (i == operands.length () - 1
/* Make sure we the offset we accumulated in a 64bit int
fits the address computation carried out in target
offset precision. */
&& (off.coeffs[0]
== sext_hwi (off.coeffs[0], TYPE_PRECISION (sizetype))))
{
gcc_assert (operands[i-1].opcode == MEM_REF);
tree ops[2];
@ -3808,7 +3813,12 @@ vn_reference_insert (tree op, tree result, tree vuse, tree vdef)
break;
off += vro->off;
}
if (i == operands.length () - 1)
if (i == operands.length () - 1
/* Make sure we the offset we accumulated in a 64bit int
fits the address computation carried out in target
offset precision. */
&& (off.coeffs[0]
== sext_hwi (off.coeffs[0], TYPE_PRECISION (sizetype))))
{
gcc_assert (operands[i-1].opcode == MEM_REF);
tree ops[2];