https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104372
Bug ID: 104372
Summary: [ARM] Unnecessary writes to stack when passing
aggregate in registers
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: palchak at google dot com
Target Milestone: ---
Missed optimization when an aggregate is passed by value entirely in registers:
struct Bar {};
struct Foo {
Bar *addr;
int size;
};
Bar* MakeBar1(Bar *addr, int) noexcept {
return addr;
}
Bar* MakeBar2(Foo foo) noexcept {
return foo.addr;
}
When compiled with '-O2' using 'arm-unknown-linux-gnueabihf-g++ (GCC) 12.0.0'
generates:
MakeBar1(Bar*, int):
bx lr
MakeBar2(Foo):
sub sp, sp, #8
add r3, sp, #8
stmdb r3, {r0, r1}
add sp, sp, #8
bx lr
The creation of a stack frame in MakeBar2 is completely unnecessary. For
comparison, Clang 11.0.1 generates identical code for both functions that
matches MakeBar1 shown here.
