[binutils-gdb] opcodes: make use of __builtin_popcount when available

[Andrew Burgess]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=46b8b3d6f87c0c65d908e3f6c83532d7286868b9

commit 46b8b3d6f87c0c65d908e3f6c83532d7286868b9
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Mon Jun 21 15:10:14 2021 +0100

    opcodes: make use of __builtin_popcount when available
    
    This commit provides a small performance improvement when starting up
    CGEN based disassemblers by making use of __builtin_popcount.
    
    The #if check used in this commit was copied from bfd/elf32-arm.c
    where __builtin_popcount is also used.
    
    I ran into this code while investigating some GDB tests that would
    occasionally timeout.  One of the reason these tests were having
    problems is that the m16c and m32c disassemblers take so long to
    initialise themselves.  Speeding up count_decodable_bits helps, but is
    not a total solution.  Still, this felt like an easy win which added
    minimal extra complexity, so I figure its worth doing.
    
    opcodes/ChangeLog:
    
            * cgen-dis.c (count_decodable_bits): Use __builtin_popcount when
            available.

Diff:
---
 opcodes/ChangeLog  | 5 +++++
 opcodes/cgen-dis.c | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/opcodes/ChangeLog b/opcodes/ChangeLog
index 0dab08e6e54..20e0524a1bf 100644
--- a/opcodes/ChangeLog
+++ b/opcodes/ChangeLog
@@ -1,3 +1,8 @@
+2021-06-22  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* cgen-dis.c (count_decodable_bits): Use __builtin_popcount when
+	available.
+
 2021-06-22  Alan Modra  <amodra@gmail.com>
 
 	* pj-dis.c (print_insn_pj): Don't print trailing tab.  Do
diff --git a/opcodes/cgen-dis.c b/opcodes/cgen-dis.c
index 6a93060edd5..1a5d1ae8459 100644
--- a/opcodes/cgen-dis.c
+++ b/opcodes/cgen-dis.c
@@ -40,6 +40,9 @@ static int
 count_decodable_bits (const CGEN_INSN *insn)
 {
   unsigned mask = CGEN_INSN_BASE_MASK (insn);
+#if GCC_VERSION >= 3004
+  return __builtin_popcount (mask);
+#else
   int bits = 0;
   unsigned m;
 
@@ -49,6 +52,7 @@ count_decodable_bits (const CGEN_INSN *insn)
 	++bits;
     }
   return bits;
+#endif
 }
 
 /* Add an instruction to the hash chain.  */