[PATCH 8.2+trunk 2/2] Set TYPE_LENGTH on a variant part

[Tom Tromey <tom@tromey.com>]

gdb represents a DW_TAG_variant_part as a union.  While normally DWARF
would not set the size of a DW_TAG_variant_part, gdb's representation
requires the TYPE_LENGTH to be set.

This patch arranges to set the TYPE_LENGTH of a variant part if it has
not already been set.

This fixes some Rust regressions when testing against a version of
rustc that emits DW_TAG_variant_part.

gdb/ChangeLog
2018-08-31  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c (dwarf2_add_field): Set the TYPE_LENGTH of the
	variant part type.
---
 gdb/ChangeLog    |  5 +++++
 gdb/dwarf2read.c | 12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 0d55fd45f5..fc9e2b943f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-08-31  Tom Tromey  <tom@tromey.com>
+
+	* dwarf2read.c (dwarf2_add_field): Set the TYPE_LENGTH of the
+	variant part type.
+
 2018-08-30  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* riscv-tdep.c (riscv_insn::decode): Decode c.addi4spn, c.sd,
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 8834d08a1c..d66dfeaf2d 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -15169,6 +15169,18 @@ dwarf2_add_field (struct field_info *fip, struct die_info *die,
       fp->type = get_die_type (die, cu);
       fp->artificial = 1;
       fp->name = "<<variant>>";
+
+      /* Normally a DW_TAG_variant_part won't have a size, but our
+	 representation requires one, so set it to the maximum of the
+	 child sizes.  */
+      if (TYPE_LENGTH (fp->type) == 0)
+	{
+	  unsigned max = 0;
+	  for (int i = 0; i < TYPE_NFIELDS (fp->type); ++i)
+	    if (TYPE_LENGTH (TYPE_FIELD_TYPE (fp->type, i)) > max)
+	      max = TYPE_LENGTH (TYPE_FIELD_TYPE (fp->type, i));
+	  TYPE_LENGTH (fp->type) = max;
+	}
     }
   else
     gdb_assert_not_reached ("missing case in dwarf2_add_field");
-- 
2.17.1