[Bug c++/51680] New: g++ 4.7 fails to inline trivial template stuff

[miles at gnu dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51680

             Bug #: 51680
           Summary: g++ 4.7 fails to inline trivial template stuff
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: mi...@gnu.org


Given the following source code (and options "-O2 -S"):

   extern void process (float);

   template<typename Fun, typename T>
   void process_fun_at (const Fun &fun, T x)
   {
     process (fun (x));
   }

   static float add1 (float x)
   {
     return x + 1;
   }

   void test (float i)
   {
     process_fun_at (add1, i);
   }

g++ 4.6 (and clang++ 3.0) produce the obvious output, inlining the template
function "process_fun_at", and the function "add1":

           .globl       test(float)
   test(float):
           addss        .LC0(%rip), %xmm0
           jmp  process(float)
   .LC0:
           .long        1065353216
           .ident       "GCC: (Debian 4.6.2-9) 4.6.2"


However g++ 4.7 produces much more awkward code, inlining nothing:

   add1(float):
           addss        .LC0(%rip), %xmm0
           ret

   void process_fun_at<float (float), float>(float ( const&)(float), float):
           subq $8, %rsp
           call *%rdi
           addq $8, %rsp
           jmp  process(float)

           .globl       test(float)
   test(float):
           movl add1(float), %edi
           jmp  void process_fun_at<float (float), float>(float (
const&)(float), float)
   .LC0:
           .long        1065353216
           .ident       "GCC: (Debian 20111210-1) 4.7.0 20111210 (experimental)
[trunk revision 182188]"


If I add the keyword "inline" to the declaration of the "process_fun_at"
template function, then g++ 4.7 inlines everything and produces the same result
as 4.6.

However my impression is that given such very simple input, it should do this
inlining automatically.

g++ version is:
(Debian 20111210-1) 4.7.0 20111210 (experimental) [trunk revision 182188]

Thanks,

-miles