bitint: Fix up lowering of bitfield loads/stores [PR114313]

The following testcase ICEs, because for large/huge _BitInt bitfield
loads/stores we use the DECL_BIT_FIELD_REPRESENTATIVE as the underlying
"var" and indexes into it can be larger than the precision of the
bitfield might normally allow.

The following patch fixes that by passing NULL_TREE type in that case
to limb_access, so that we always return m_limb_type type and don't
do the extra assertions, after all, the callers expect that too.
I had to add the first hunk to avoid ICE, it was using type in one place
even when it was NULL.  But TYPE_SIZE (TREE_TYPE (var)) seems like the
right size to use anyway because the code uses VIEW_CONVERT_EXPR on it.

2024-03-13  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/114313
	* gimple-lower-bitint.cc (bitint_large_huge::limb_access): Use
	TYPE_SIZE of TREE_TYPE (var) rather than TYPE_SIZE of type.
	(bitint_large_huge::handle_load): Pass NULL_TREE rather than
	rhs_type to limb_access for the bitfield load cases.
	(bitint_large_huge::lower_mergeable_stmt): Pass NULL_TREE rather than
	lhs_type to limb_access if nlhs is non-NULL.

	* gcc.dg/torture/bitint-62.c: New test.

2 files changed, 36 insertions, 7 deletions

diff --git a/gcc/gimple-lower-bitint.cc b/gcc/gimple-lower-bitint.cc
index 65e4ab3..b58220f 100644
--- a/gcc/gimple-lower-bitint.cc
+++ b/gcc/gimple-lower-bitint.cc
@@ -640,7 +640,7 @@ bitint_large_huge::limb_access (tree type, tree var, tree idx, bool write_p)
 					 TREE_TYPE (TREE_TYPE (var))))
 	{
 	  unsigned HOST_WIDE_INT nelts
-	    = CEIL (tree_to_uhwi (TYPE_SIZE (type)), limb_prec);
+	    = CEIL (tree_to_uhwi (TYPE_SIZE (TREE_TYPE (var))), limb_prec);
 	  tree atype = build_array_type_nelts (ltype, nelts);
 	  var = build1 (VIEW_CONVERT_EXPR, atype, var);
 	}
@@ -1854,7 +1854,7 @@ bitint_large_huge::handle_load (gimple *stmt, tree idx)
 		m_gsi = gsi_after_labels (gsi_bb (m_gsi));
 	      else
 		gsi_next (&m_gsi);
-	      tree t = limb_access (rhs_type, nrhs1, size_int (bo_idx), true);
+	      tree t = limb_access (NULL_TREE, nrhs1, size_int (bo_idx), true);
 	      tree iv = make_ssa_name (m_limb_type);
 	      g = gimple_build_assign (iv, t);
 	      insert_before (g);
@@ -1941,7 +1941,7 @@ bitint_large_huge::handle_load (gimple *stmt, tree idx)
       tree iv2 = NULL_TREE;
       if (nidx0)
 	{
-	  tree t = limb_access (rhs_type, nrhs1, nidx0, true);
+	  tree t = limb_access (NULL_TREE, nrhs1, nidx0, true);
 	  iv = make_ssa_name (m_limb_type);
 	  g = gimple_build_assign (iv, t);
 	  insert_before (g);
@@ -1966,7 +1966,7 @@ bitint_large_huge::handle_load (gimple *stmt, tree idx)
 	      if_then (g, profile_probability::likely (),
 		       edge_true, edge_false);
 	    }
-	  tree t = limb_access (rhs_type, nrhs1, nidx1, true);
+	  tree t = limb_access (NULL_TREE, nrhs1, nidx1, true);
 	  if (m_upwards_2limb
 	      && !m_first
 	      && !m_bitfld_load
@@ -2728,8 +2728,8 @@ bitint_large_huge::lower_mergeable_stmt (gimple *stmt, tree_code &cmp_code,
 	      /* Otherwise, stores to any other lhs.  */
 	      if (!done)
 		{
-		  tree l = limb_access (lhs_type, nlhs ? nlhs : lhs,
-					nidx, true);
+		  tree l = limb_access (nlhs ? NULL_TREE : lhs_type,
+					nlhs ? nlhs : lhs, nidx, true);
 		  g = gimple_build_assign (l, rhs1);
 		}
 	      insert_before (g);
@@ -2873,7 +2873,8 @@ bitint_large_huge::lower_mergeable_stmt (gimple *stmt, tree_code &cmp_code,
 	  /* Otherwise, stores to any other lhs.  */
 	  if (!done)
 	    {
-	      tree l = limb_access (lhs_type, nlhs ? nlhs : lhs, nidx, true);
+	      tree l = limb_access (nlhs ? NULL_TREE : lhs_type,
+				    nlhs ? nlhs : lhs, nidx, true);
 	      g = gimple_build_assign (l, rhs1);
 	    }
 	  insert_before (g);
diff --git a/gcc/testsuite/gcc.dg/torture/bitint-62.c b/gcc/testsuite/gcc.dg/torture/bitint-62.c
new file mode 100644
index 0000000..0dd5ad8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/bitint-62.c
@@ -0,0 +1,28 @@
+/* PR middle-end/114313 */
+/* { dg-do run { target bitint } } */
+/* { dg-options "-std=c23" } */
+/* { dg-skip-if "" { ! run_expensive_tests }  { "*" } { "-O0" "-O2" } } */
+/* { dg-skip-if "" { ! run_expensive_tests } { "-flto" } { "" } } */
+
+#if __BITINT_MAXWIDTH__ >= 256
+struct S { _BitInt(257) : 257; _BitInt(256) b : 182; } s;
+
+__attribute__((noipa)) _BitInt(256)
+foo (void)
+{
+  return s.b;
+}
+#endif
+
+int
+main ()
+{
+#if __BITINT_MAXWIDTH__ >= 256
+  s.b = 1414262180967678524960294186228886540125217087586381431wb;
+  if (foo () != 1414262180967678524960294186228886540125217087586381431wb)
+    __builtin_abort ();
+  s.b = -581849792837428541666755934071828568425158644418477999wb;
+  if (foo () != -581849792837428541666755934071828568425158644418477999wb)
+    __builtin_abort ();
+#endif
+}