http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55747
Bug #: 55747
Summary: Extra registers are saved in functions that only call
noreturn functions
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: josh.m.con...@gmail.com
On architectures such as ARM, where a link register is used to save the return
address, this value does not need to be saved in a function that only calls
noreturn functions.
For example, if I build the following source:
__attribute__((noreturn))
extern void bar (void);
int x;
void foo (void)
{
if (x)
bar ();
}
Using the options "-O2", the link register is saved:
stmfd sp!, {r3, lr}
...
ldmeqfd sp!, {r3, pc}
However, this is unnecessary since the only way the link register cannot be
corrupted since any calls to "bar" will not return.
Note that I am not filing this as an ARM target bug since the issue appears to
be a general problem related to dataflow analysis not tracking the difference
between calls to normal functions and calls to noreturn functions. At any
rate, I see a similar problem in our custom target as well.
