[gcc r13-205] tree-optimization/105517 - avoid offset truncation during VN

[gcc r13-205] tree-optimization/105517 - avoid offset truncation during VN

[Richard Biener]

https://gcc.gnu.org/g:faabc751d0bb7e7fe86abfe8991b0307d585874a

commit r13-205-gfaabc751d0bb7e7fe86abfe8991b0307d585874a
Author: Richard Biener <rguenther@suse.de>
Date:   Mon May 9 11:33:44 2022 +0200

    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:
---
 gcc/poly-int.h        | 13 +++++++++++++
 gcc/tree-ssa-sccvn.cc | 14 ++++++++++++--
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/gcc/poly-int.h b/gcc/poly-int.h
index 2bf9d98599f..d085544a57e 100644
--- 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 76587632312..3732d06b0bb 100644
--- 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];