[PATCH V2] improve bitmap / sbitmap compatability of bitmap_set_bit

[tbsaunde+gcc]

From: Trevor Saunders <tbsaunde+...@tbsaunde.org>

This makes the sbitmap version return true if the bit was previously
unset to make it similar to the bitmap version.

I believe I fixed up the comments from may, and rebootstrapped + regtested
ppc64le-linux-gnu, ok?

Trev

gcc/ChangeLog:

2017-07-20  Trevor Saunders  <tbsaunde+...@tbsaunde.org>

        * sbitmap.h (bitmap_set_bit): Return bool similar to bitmap
        version of this function.
---
 gcc/ChangeLog |  5 +++++
 gcc/sbitmap.h | 12 ++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ef0e7881073..8d171b1a8a5 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2017-07-20  Trevor Saunders  <tbsaunde+...@tbsaunde.org>
+
+       * sbitmap.h (bitmap_set_bit): Return bool similar to bitmap
+       version of this function.
+
 2017-07-18  Uros Bizjak  <ubiz...@gmail.com>
 
        PR target/81471
diff --git a/gcc/sbitmap.h b/gcc/sbitmap.h
index ce4d27d927c..6f90fc877d4 100644
--- a/gcc/sbitmap.h
+++ b/gcc/sbitmap.h
@@ -104,13 +104,17 @@ bitmap_bit_p (const_sbitmap map, int bitno)
   return (map->elms[i] >> s) & (SBITMAP_ELT_TYPE) 1;
 }
 
-/* Set bit number BITNO in the sbitmap MAP.  */
+/* Set bit number BITNO in the sbitmap MAP.  Return true if it was
+   previously unset.  */
 
-static inline void
+static inline bool
 bitmap_set_bit (sbitmap map, int bitno)
 {
-  map->elms[bitno / SBITMAP_ELT_BITS]
-    |= (SBITMAP_ELT_TYPE) 1 << (bitno) % SBITMAP_ELT_BITS;
+  SBITMAP_ELT_TYPE *word = &map->elms[bitno / SBITMAP_ELT_BITS];
+  SBITMAP_ELT_TYPE mask = (SBITMAP_ELT_TYPE) 1 << (bitno) % SBITMAP_ELT_BITS;
+  bool ret = (*word & mask) == 0;
+  *word |= mask;
+  return ret;
 }
 
 /* Reset bit number BITNO in the sbitmap MAP.  */
-- 
2.11.0