[Bug ipa/78555] New: gcc/sreal.c:232:20: runtime error: left shift of negative value -2018967552

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78555

            Bug ID: 78555
           Summary: gcc/sreal.c:232:20: runtime error: left shift of
                    negative value -2018967552
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: trippels at gcc dot gnu.org
  Target Milestone: ---

bootstrap-ubsan on ppc64le hits the following error very often:

 gcc/sreal.c:232:20: runtime error: left shift of negative value -2018967552

I will test:

diff --git a/gcc/sreal.c b/gcc/sreal.c
index 9c43b4e..ceb63b7 100644
--- a/gcc/sreal.c
+++ b/gcc/sreal.c
@@ -227,9 +227,10 @@ sreal::operator* (const sreal &other) const
 sreal
 sreal::operator/ (const sreal &other) const
 {
+  int64_t sign = m_sig < 0 ? -1 : 1;
   gcc_checking_assert (other.m_sig != 0);
   sreal r;
-  r.m_sig = (m_sig << SREAL_PART_BITS) / other.m_sig;
+  r.m_sig = sign * (absu_hwi (m_sig) << SREAL_PART_BITS) / other.m_sig;
   r.m_exp = m_exp - other.m_exp - SREAL_PART_BITS;
   r.normalize ();
   return r;