[Bug ipa/64164] New: [4.9/5 Regression] one more stack slot used due to one less inlining level

[patrick.marlier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64164

            Bug ID: 64164
           Summary: [4.9/5 Regression] one more stack slot used due to one
                    less inlining level
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick.marlier at gmail dot com
              Host: x86_64-linux-gnu
            Target: x86_64-linux-gnu
             Build: x86_64-linux-gnu

Created attachment 34178
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34178&action=edit
testcase

$ cc -O2 -S -o stm.s stm.c
$ cc -O2 -DOPT -S -o stm-opt.s stm.c

if you compare the 2 outputs, stm_load function is using one more slot on the
stack.
The difference is only this:

static inline size_t
AO_myload2(const volatile size_t *addr)
{
  return *(size_t *)addr;
}
static inline size_t
AO_myload(const volatile size_t *addr)
{
#ifdef OPT
  size_t result = AO_myload2(addr);
#else
  size_t result = *(size_t *)addr;
#endif
  return result;
}

Having one more inlined function should have the same optimization not a better
one.
4.8 does not have the problem and the code generated is the same.