https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98292
Bug ID: 98292
Summary: Optimize away C return; in function returning
integral/pointer
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
This is related to the PR94779, but that one talks just about switches.
int
foo (int x)
{
if (x > 20)
return x;
}
int
bar (int x)
{
if (x > 30)
return 30;
}
int
baz (int x)
{
if (x > 40)
return x + 1U;
}
int
qux (int x)
{
if (x > 50)
return x | 32;
}
is optimized to just the return statement in C++ (because we add
__builtin_unreachable() in that case), but not in C.
I think we should do that also in C, provided that there are no non-debug
non-CLOBBER stmts on the branch with GIMPLE_RETURN without argument, and
provided that on the other branch there are just very few cheap stmts
guaranteed not to invoke UB/trap (appart from debug/CLOBBER stmts) plus the
GIMPLE_RETURN with argument.
LLVM seems to optimize that (though not sure if it isn't because it incorrectly
adds something like __builtin_unreachable () even for C).
