on ARRAY_REFs sign-extend offsets only from sizetype's precision [PR98255]

As discussed in the PR, the problem here is that the routines changed in
this patch sign extend the difference of index and low_bound from the
precision of the index, so e.g. when index is unsigned int and contains
value -2U, we treat it as index -2 rather than 0x00000000fffffffeU on 64-bit
arches.
On the other hand, get_inner_reference which is used during expansion, does:
            if (! integer_zerop (low_bound))
              index = fold_build2 (MINUS_EXPR, TREE_TYPE (index),
                                   index, low_bound);

            offset = size_binop (PLUS_EXPR, offset,
                                 size_binop (MULT_EXPR,
                                             fold_convert (sizetype, index),
                                             unit_size));
which effectively requires that either low_bound is constant 0 and then
index in ARRAY_REFs can be arbitrary type which is then sign or zero
extended to sizetype, or low_bound is something else and then index and
low_bound must have compatible types and it is still converted afterwards to
sizetype and from there then a few lines later:
expr.c-  if (poly_int_tree_p (offset))
expr.c-    {
expr.c:      poly_offset_int tem = wi::sext (wi::to_poly_offset (offset),
expr.c-                               TYPE_PRECISION (sizetype));
The following patch makes those routines match what get_inner_reference is
doing.

2021-01-22  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/98255
	* tree-dfa.c (get_ref_base_and_extent): For ARRAY_REFs, sign
	extend index - low_bound from sizetype's precision rather than index
	precision.
	(get_addr_base_and_unit_offset_1): Likewise.
	* tree-ssa-sccvn.c (ao_ref_init_from_vn_reference): Likewise.
	* gimple-fold.c (fold_const_aggregate_ref_1): Likewise.

	* gcc.dg/pr98255.c: New test.

gcc/gimple-fold.c

@@ -8007,7 +8007,7 @@ fold_const_aggregate_ref_1 (tree t, tree (*valueize) (tree))
 	      poly_offset_int woffset
 		= wi::sext (wi::to_poly_offset (idx)
 			    - wi::to_poly_offset (low_bound),
-			    TYPE_PRECISION (TREE_TYPE (idx)));
+			    TYPE_PRECISION (sizetype));
 	      woffset *= tree_to_uhwi (unit_size);
 	      woffset *= BITS_PER_UNIT;
 	      if (woffset.to_shwi (&offset))

gcc/testsuite/gcc.dg/pr98255.c

@@ -0,0 +1,49 @@
+/* PR tree-optimization/98255 */
+/* { dg-do run } */
+/* { dg-options "-Os" } */
+/* { dg-additional-options "-fPIC" { target fpic } } */
+
+struct A { volatile unsigned b; unsigned c; };
+int d, *e, h, k, l;
+static struct A f;
+long g;
+static unsigned i = -2U;
+volatile int j;
+
+long
+foo (void)
+{
+  char n[4][4][3]
+    = { { {9, 2, 8}, {9, 2, 8}, {9, 2, 8}, {9} }, { {8} }, { {8} }, { {2} } };
+  while (d)
+    {
+      for (; f.c < 4; f.c++)
+	{
+	  *e = 0;
+	  h = n[f.c + 4][0][d];
+	}
+      while (g)
+	return n[0][3][i];
+      while (1)
+	{
+	  if (k)
+	    {
+	      j = 0;
+	      if (j)
+		continue;
+	    }
+	  if (l)
+	    break;
+	}
+    }
+  return 0;
+}
+
+int
+main ()
+{
+  asm volatile ("" : "+g" (d), "+g" (g), "+g" (f.c));
+  asm volatile ("" : "+g" (e), "+g" (k), "+g" (l));
+  foo ();
+  return 0;
+}

gcc/tree-dfa.c

@@ -503,7 +503,7 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
 		poly_offset_int woffset
 		  = wi::sext (wi::to_poly_offset (index)
 			      - wi::to_poly_offset (low_bound),
-			      TYPE_PRECISION (TREE_TYPE (index)));
+			      TYPE_PRECISION (sizetype));
 		woffset *= wi::to_offset (unit_size);
 		woffset <<= LOG2_BITS_PER_UNIT;
 		bit_offset += woffset;
@@ -564,7 +564,7 @@ get_ref_base_and_extent (tree exp, poly_int64_pod *poffset,
 		      {
 			poly_offset_int woffset
 			  = wi::sext (omin - lbound,
-				      TYPE_PRECISION (TREE_TYPE (index)));
+				      TYPE_PRECISION (sizetype));
 			woffset *= wi::to_offset (unit_size);
 			woffset <<= LOG2_BITS_PER_UNIT;
 			bit_offset += woffset;
@@ -822,7 +822,7 @@ get_addr_base_and_unit_offset_1 (tree exp, poly_int64_pod *poffset,
 	    poly_offset_int woffset
 		= wi::sext (wi::to_poly_offset (index)
 			    - wi::to_poly_offset (low_bound),
-			    TYPE_PRECISION (TREE_TYPE (index)));
+			    TYPE_PRECISION (sizetype));
 	    woffset *= wi::to_offset (unit_size);
 	    byte_offset += woffset.force_shwi ();
 	  }

gcc/tree-ssa-sccvn.c

@@ -1108,7 +1108,7 @@ ao_ref_init_from_vn_reference (ao_ref *ref,
 	      poly_offset_int woffset
 		= wi::sext (wi::to_poly_offset (op->op0)
 			    - wi::to_poly_offset (op->op1),
-			    TYPE_PRECISION (TREE_TYPE (op->op0)));
+			    TYPE_PRECISION (sizetype));
 	      woffset *= wi::to_offset (op->op2) * vn_ref_op_align_unit (op);
 	      woffset <<= LOG2_BITS_PER_UNIT;
 	      offset += woffset;