https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67287
Bug ID: 67287
Summary: FRE should CSE sqrt() calls even with -ferrno-math
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
double sqrt(double x);
double t (double x)
{
double a = sqrt (x);
double b = sqrt (x);
return a * b;
}
should be optimized to
double t (double x)
{
double a = sqrt (x);
return a * a;
}
with -fmath-errno. FRE currently gives up too early and the alias oracle
can handle errno-style references (but it can't use a call as a "ref", so
the "errno"-only side-effect has to be modeled by creating a special ref
for performing the walking for math builtins setting errno as their only
side-effect).
We may not miscompile
sqrt (x);
errno = 0;
sqrt (x);
if (errno != 0)
...
to CSE the second sqrt.
