[PATCH] tree-optimization/126650 - get_inner_reference_aff and bitfields

get_inner_reference_aff tries to compensate for bit precision
offsets and sizes by rounding down and up, but fails to do this
correctly.  The following makes it more obviously correct by
rounding positions and computing the rounded size based on those.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	PR tree-optimization/126650
	* tree-affine.cc (get_inner_reference_aff): Fixup rounding
	of size.

	* gcc.dg/torture/pr126650.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr126650.c | 35 +++++++++++++++++++++++++
 gcc/tree-affine.cc                      |  5 ++--
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr126650.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr126650.c b/gcc/testsuite/gcc.dg/torture/pr126650.c
new file mode 100644
index 00000000000..166705d9cfe
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr126650.c
@@ -0,0 +1,35 @@
+/* { dg-do run } */
+
+#include <stdarg.h>
+#include <stdlib.h>
+
+long a;
+
+void __attribute__((noipa)) foo (int n, ...)
+{
+  va_list list;
+  va_start (list, n);
+  int val = va_arg (list, int);
+  if (val != -64)
+    abort ();
+  va_end (list);
+}
+
+int main()
+{
+  struct b {
+    int : 7;
+    int : 2;
+    int : 6;
+    int : 3;
+    int c : 7;
+  };
+  union {
+    int d;
+    struct b bf;
+    char e[4];
+  } f;
+  f.d = a;
+  f.e[3] = 7;
+  foo (1, f.bf.c);
+}
diff --git a/gcc/tree-affine.cc b/gcc/tree-affine.cc
index b5b7249c675..181fd6fb33c 100644
--- a/gcc/tree-affine.cc
+++ b/gcc/tree-affine.cc
@@ -1030,10 +1030,11 @@ get_inner_reference_aff (tree ref, aff_tree *addr, poly_widest_int *size)
       aff_combination_add (addr, &tmp);
     }
 
-  aff_combination_const (&tmp, sizetype, bits_to_bytes_round_down (bitpos));
+  poly_int64 bytepos = bits_to_bytes_round_down (bitpos);
+  aff_combination_const (&tmp, sizetype, bytepos);
   aff_combination_add (addr, &tmp);
 
-  *size = bits_to_bytes_round_up (bitsize);
+  *size = bits_to_bytes_round_up (bitpos + bitsize) - bytepos;
 
   return base;
 }
-- 
2.51.0