[PATCH] sccvn: Fix handling of POINTER_PLUS_EXPR in memset offset [PR93582]

[Jakub Jelinek]

Hi!

On Wed, Mar 04, 2020 at 11:33:06AM +0100, Richard Biener wrote:
> > where POINTER_PLUS_EXPR last operand has sizetype type, thus unsigned,
> > and in the testcase gimple_assign_rhs2 (def) is thus 0xf000000000000001ULL
> > which multiplied by 8 doesn't fit into signed HWI.  If it would be treated
> > as signed offset instead, it would fit (-0xfffffffffffffffLL, multiplied
> > by 8 is -0x7ffffffffffffff8LL).  Unfortunately with the poly_int obfuscation
> > I'm not sure how to convert it from unsigned to signed poly_int.
> 
> mem_ref_offset provides a boiler-plate for this:
> 
> poly_offset_int::from (wi::to_poly_wide (TREE_OPERAND (t, 1)), SIGNED);

Thanks, that seems to work.
So, is the following ok for trunk if it passes bootstrap/regtest?
The test now works on both big-endian and little-endian.

2020-03-04  Richard Biener  <rguenther@suse.de>
	    Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/93582
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Treat POINTER_PLUS_EXPR
	last operand as signed when looking for memset offset.  Formatting
	fix.

	* gcc.dg/tree-ssa/pr93582-11.c: New test.

--- gcc/tree-ssa-sccvn.c.jj	2020-03-04 12:46:09.809610729 +0100
+++ gcc/tree-ssa-sccvn.c	2020-03-04 13:07:07.982902846 +0100
@@ -2656,7 +2656,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree
 	{
 	  poly_int64 soff;
 	  if (TREE_CODE (base) != MEM_REF
-	      || !(mem_ref_offset (base) << LOG2_BITS_PER_UNIT).to_shwi (&soff))
+	      || !(mem_ref_offset (base)
+		   << LOG2_BITS_PER_UNIT).to_shwi (&soff))
 	    return (void *)-1;
 	  offset += soff;
 	  offset2 = 0;
@@ -2666,10 +2667,13 @@ vn_reference_lookup_3 (ao_ref *ref, tree
 	      if (is_gimple_assign (def)
 		  && gimple_assign_rhs_code (def) == POINTER_PLUS_EXPR
 		  && gimple_assign_rhs1 (def) == TREE_OPERAND (base, 0)
-		  && poly_int_tree_p (gimple_assign_rhs2 (def))
-		  && (wi::to_poly_offset (gimple_assign_rhs2 (def))
-		      << LOG2_BITS_PER_UNIT).to_shwi (&offset2))
+		  && poly_int_tree_p (gimple_assign_rhs2 (def)))
 		{
+		  tree rhs2 = gimple_assign_rhs2 (def);
+		  if (!(poly_offset_int::from (wi::to_poly_wide (rhs2),
+					       SIGNED)
+			<< LOG2_BITS_PER_UNIT).to_shwi (&offset2))
+		    return (void *)-1;
 		  ref2 = gimple_assign_rhs1 (def);
 		  if (TREE_CODE (ref2) == SSA_NAME)
 		    ref2 = SSA_VAL (ref2);
--- gcc/testsuite/gcc.dg/tree-ssa/pr93582-11.c.jj	2020-03-04 13:12:22.819222647 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/pr93582-11.c	2020-03-04 13:13:47.234968590 +0100
@@ -0,0 +1,16 @@
+/* PR tree-optimization/93582 */
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+/* { dg-final { scan-tree-dump "return 9223372036854775806;" "fre1" } } */
+
+union U { struct A { unsigned long long a : 1, b : 62, c : 1; } a; unsigned long long i; };
+
+unsigned long long
+foo (char *p)
+{
+  __builtin_memset (p - 0xfffffffffffffffULL, 0, 0xffffffffffffffeULL);
+  __builtin_memset (p + 1, 0, 0xffffffffffffffeULL);
+  union U *q = (union U *) (void *) (p - 4);
+  q->a.b = -1;
+  return q->i;
+}


	Jakub