http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55026
Bug #: 55026
Summary: [Multiple targets] Inefficient code with structs
passed by value
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: m...@mansr.com
Multiple targets (including ARM, HPPA, and MIPS) generate inefficient code in
functions taking struct arguments by value. Consider this code:
struct foo {
int a;
int b;
};
int f(struct foo x)
{
return x.a + x.b;
}
On ARM, this compiles to the following at -O3 optimisation:
f:
@ args = 0, pretend = 0, frame = 8
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
sub sp, sp, #8
add r3, sp, #8
stmdb r3, {r0, r1}
ldmia sp, {r0, r3}
add r0, r0, r3
add sp, sp, #8
@ sp needed
bx lr
Note the entirely unnecessary (and inefficiently done to boot) storing and
loading of the argument registers to/from the stack.
The x86_64 and SH4 targets do not show this behaviour.
