[PATCH] gimple-fold: Handle _BitInt in __builtin_clear_padding [PR102989]

[Jakub Jelinek <jakub@redhat.com>]

Hi!

The comments about _Atomic _BitInt made me figure out I forgot (although
earlier was planning to do that) to implement __builtin_clear_padding
support for _BitInt.

The following patch (incremental to the _BitInt series) does that.

2023-07-28  Jakub Jelinek  <jakub@redhat.com>

	PR c/102989
	* gimple-fold.cc (clear_padding_unit): Mention in comment that
	_BitInt types don't need to fit either.
	(clear_padding_bitint_needs_padding_p): New function.
	(clear_padding_type_may_have_padding_p): Handle BITINT_TYPE.
	(clear_padding_type): Likewise.

	* gcc.dg/bitint-16.c: New test.

--- gcc/gimple-fold.cc.jj	2023-07-11 15:28:54.704679510 +0200
+++ gcc/gimple-fold.cc	2023-07-28 12:37:18.971789595 +0200
@@ -4103,8 +4103,8 @@ gimple_fold_builtin_realloc (gimple_stmt
   return false;
 }
 
-/* Number of bytes into which any type but aggregate or vector types
-   should fit.  */
+/* Number of bytes into which any type but aggregate, vector or
+   _BitInt types should fit.  */
 static constexpr size_t clear_padding_unit
   = MAX_BITSIZE_MODE_ANY_MODE / BITS_PER_UNIT;
 /* Buffer size on which __builtin_clear_padding folding code works.  */
@@ -4595,6 +4595,26 @@ clear_padding_real_needs_padding_p (tree
 	  && (fmt->signbit_ro == 79 || fmt->signbit_ro == 95));
 }
 
+/* _BitInt has padding bits if it isn't extended in the ABI and has smaller
+   precision than bits in limb or corresponding number of limbs.  */
+
+static bool
+clear_padding_bitint_needs_padding_p (tree type)
+{
+  struct bitint_info info;
+  gcc_assert (targetm.c.bitint_type_info (TYPE_PRECISION (type), &info));
+  if (info.extended)
+    return false;
+  scalar_int_mode limb_mode = as_a <scalar_int_mode> (info.limb_mode);
+  if (TYPE_PRECISION (type) < GET_MODE_PRECISION (limb_mode))
+    return true;
+  else if (TYPE_PRECISION (type) == GET_MODE_PRECISION (limb_mode))
+    return false;
+  else
+    return (((unsigned) TYPE_PRECISION (type))
+	    % GET_MODE_PRECISION (limb_mode)) != 0;
+}
+
 /* Return true if TYPE might contain any padding bits.  */
 
 bool
@@ -4611,6 +4631,8 @@ clear_padding_type_may_have_padding_p (t
       return clear_padding_type_may_have_padding_p (TREE_TYPE (type));
     case REAL_TYPE:
       return clear_padding_real_needs_padding_p (type);
+    case BITINT_TYPE:
+      return clear_padding_bitint_needs_padding_p (type);
     default:
       return false;
     }
@@ -4855,6 +4877,57 @@ clear_padding_type (clear_padding_struct
       memset (buf->buf + buf->size, ~0, sz);
       buf->size += sz;
       break;
+    case BITINT_TYPE:
+      {
+	struct bitint_info info;
+	gcc_assert (targetm.c.bitint_type_info (TYPE_PRECISION (type), &info));
+	scalar_int_mode limb_mode = as_a <scalar_int_mode> (info.limb_mode);
+	if (TYPE_PRECISION (type) <= GET_MODE_PRECISION (limb_mode))
+	  {
+	    gcc_assert ((size_t) sz <= clear_padding_unit);
+	    if ((unsigned HOST_WIDE_INT) sz + buf->size
+		> clear_padding_buf_size)
+	      clear_padding_flush (buf, false);
+	    if (!info.extended
+		&& TYPE_PRECISION (type) < GET_MODE_PRECISION (limb_mode))
+	      {
+		int tprec = GET_MODE_PRECISION (limb_mode);
+		int prec = TYPE_PRECISION (type);
+		tree t = build_nonstandard_integer_type (tprec, 1);
+		tree cst = wide_int_to_tree (t, wi::mask (prec, true, tprec));
+		int len = native_encode_expr (cst, buf->buf + buf->size, sz);
+		gcc_assert (len > 0 && (size_t) len == (size_t) sz);
+	      }
+	    else
+	      memset (buf->buf + buf->size, 0, sz);
+	    buf->size += sz;
+	    break;
+	  }
+	tree limbtype
+	  = build_nonstandard_integer_type (GET_MODE_PRECISION (limb_mode), 1);
+	fldsz = int_size_in_bytes (limbtype);
+	nelts = int_size_in_bytes (type) / fldsz;
+	for (HOST_WIDE_INT i = 0; i < nelts; i++)
+	  {
+	    if (!info.extended
+		&& i == (info.big_endian ? 0 : nelts - 1)
+		&& (((unsigned) TYPE_PRECISION (type))
+		    % TYPE_PRECISION (limbtype)) != 0)
+	      {
+		int tprec = GET_MODE_PRECISION (limb_mode);
+		int prec = (((unsigned) TYPE_PRECISION (type)) % tprec);
+		tree cst = wide_int_to_tree (limbtype,
+					     wi::mask (prec, true, tprec));
+		int len = native_encode_expr (cst, buf->buf + buf->size,
+					      fldsz);
+		gcc_assert (len > 0 && (size_t) len == (size_t) fldsz);
+		buf->size += fldsz;
+	      }
+	    else
+	      clear_padding_type (buf, limbtype, fldsz, for_auto_init);
+	  }
+	break;
+      }
     default:
       gcc_assert ((size_t) sz <= clear_padding_unit);
       if ((unsigned HOST_WIDE_INT) sz + buf->size > clear_padding_buf_size)
--- gcc/testsuite/gcc.dg/bitint-16.c.jj	2023-07-28 12:47:37.641180784 +0200
+++ gcc/testsuite/gcc.dg/bitint-16.c	2023-07-28 12:47:30.488280320 +0200
@@ -0,0 +1,31 @@
+/* PR c/102989 */
+/* { dg-do compile { target bitint } } */
+/* { dg-options "-O2 -std=c2x -pedantic-errors" } */
+
+_BitInt(15) a;
+_BitInt(42) b;
+#if __BITINT_MAXWIDTH__ >= 115
+_BitInt(115) c;
+#endif
+#if __BITINT_MAXWIDTH__ >= 192
+_BitInt(192) d;
+#endif
+#if __BITINT_MAXWIDTH__ >= 575
+_BitInt(575) e;
+#endif
+
+int
+main ()
+{
+  __builtin_clear_padding (&a);
+  __builtin_clear_padding (&b);
+#if __BITINT_MAXWIDTH__ >= 115
+  __builtin_clear_padding (&c);
+#endif
+#if __BITINT_MAXWIDTH__ >= 192
+  __builtin_clear_padding (&d);
+#endif
+#if __BITINT_MAXWIDTH__ >= 575
+  __builtin_clear_padding (&e);
+#endif
+}

	Jakub