[Bug tree-optimization/93447] New: Value range propagation not working at -Os

[pskocik at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93447

            Bug ID: 93447
           Summary: Value range propagation not working at -Os
           Product: gcc
           Version: 9.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pskocik at gmail dot com
  Target Milestone: ---

I have a lot of cases where I'd like to translate boolean conditions to negated
errno codes (possibly wrapped in an struct or a trivial union).

If this translation is inlinable, I'd expect that undoing it to get a boolean
again (bool => negated errno => bool) would eliminate the roundtrip.

GCC indeed does this at -O2 and -O3, but the optimization's failing to kick in
at -Os, leading to code size increases.

Clang succeeds at eliminating the roundrip at -Os (and it does this
optimization already at -O1).

A simple example that generates unnecessary code at -Os:

#include <errno.h>

_Bool addb_simple(int A, int B, int *Rp)
{
    int ec=0;
    if(__builtin_add_overflow(A,B,Rp)) 
        ec = -ERANGE;
    return !!ec;
}

https://gcc.godbolt.org/z/tGkbtD


Thanks for looking into it!