tree-optimization/105517 - avoid offset truncation during VN

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.

diff --git a/gcc/poly-int.h b/gcc/poly-int.h
index 2bf9d98599fd6ffde7eb78eb0427c6eb2b388d2e..d085544a57e94ddb1d96e2140e9ddf9d47711424 100644 (file)
--- a/gcc/poly-int.h
+++ b/gcc/poly-int.h
@@ -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.  */
 

diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 76587632312738fd77b636478880bf7a30be4611..3732d06b0bb0421fe2bafa862af37fcb50269386 100644 (file)
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -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];