[Bug ipa/87254] New: Inlining clones in trivial wrappers

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87254

            Bug ID: 87254
           Summary: Inlining clones in trivial wrappers
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

int h();
static int f(int j,double*a){
  if(j)
  {
    double t[1024];
    for(int i=0;i<1024;++i){t[i]=i;}
    return t[(int)*a];
  }
  else
    return h();
}
int g(double*a){return f(0,a);}

Compiled with -O3.

The code in f is random crap, the key elements to reproduce are:
- f is not inlined in einline,
- f is cloned in IPA-CP,
- the clone of f is not inlined in g.

(so a simpler reproducer may be possible with -fdisable-tree-einline --param
ipa-cp-eval-threshold=10)

The first 2 steps are normal, but the last one seems wrong to me. There is
nothing to lose by inlining f's clone into the trivial wrapper that is its only
caller. The inline dump complains that "--param large-stack-frame-growth limit
reached", but changing this param has no effect, I have to change
"large-stack-frame" instead to convince it to inline.


Just in case, before that I was investigating

static int f(int j,double*a){
  if(j)
  {
    double t[1024];
    for(int i=0;i<1024;++i){t[i]=i;}
    return t[(int)*a];
  }
  else
  {
    float t[1024];
    for(int i=0;i<1024;++i){t[i]=i;}
    return t[(int)*a];
  }
}
int g(double*a){return f(0,a);}
int h(double*a){return f(1,a);}

with -O3 -fdisable-tree-einline --param ipa-cp-eval-threshold=10 .

In the past, I have seen such trivial left-over wrappers with -flto on GMP (
https://gmplib.org/list-archives/gmp-devel/2018-April/004874.html ), and I was
reminded of it by https://stackoverflow.com/q/51152215/1918193 .