http://llvm.org/bugs/show_bug.cgi?id=8186
Summary: -O3 does not imply -fomit-frame-pointer
Product: clang
Version: 2.7
Platform: PC
OS/Version: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: LLVM Codegen
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
I compiled the following source using clang-2.7 -O3 on Debian sid amd64:
=====
struct buffer {
const char *data;
unsigned int length;
};
void buffer_inplace_advance(struct buffer *b, unsigned int length) {
b->data += length;
b->length -= length;
}
=====
This is a disassembly:
=====
Dump of assembler code for function buffer_inplace_advance:
0x0000000000400760 <+0>: push %rbp
0x0000000000400761 <+1>: mov %rsp,%rbp
0x0000000000400764 <+4>: mov %esi,%eax
0x0000000000400766 <+6>: add %rax,(%rdi)
0x0000000000400769 <+9>: sub %eax,0x8(%rdi)
0x000000000040076c <+12>: pop %rbp
0x000000000040076d <+13>: retq
=====
As you can see it contains a frame pointer. Turning on -fomit-frame-pointer in
addition to -O3 makes the code much shorter. For gcc -fomit-frame-pointer is
implied in -O3 on this architecture, so clang should probably do this, too.
According to baldrick (irc). This bug is reproducible on 2.8, too.
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