https://bugs.llvm.org/show_bug.cgi?id=41318
Bug ID: 41318
Summary: Stack realignment produces inefficient code
Product: new-bugs
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
-mstackrealign or __attribute__((force_align_arg_pointer)) in combination with
-mstack-alignment=32 (or larger) emits an unnecessary instruction.
Minimal test case:
void foo(void);
__attribute__((force_align_arg_pointer))
void bar(void) {
foo();
}
-O3 -mstack-alignment=16
<bar>:
55 push rbp
48 89 e5 mov rbp,rsp
48 83 e4 f0 and rsp,0xfffffffffffffff0
e8 00 00 00 00 call <foo>
48 89 ec mov rsp,rbp
5d pop rbp
c3 ret
-O3 -mstack-alignment=32
<bar>:
55 push rbp
48 89 e5 mov rbp,rsp
48 83 e4 e0 and rsp,0xffffffffffffffe0
48 83 ec 20 sub rsp,0x20 <- This is completely redundant
e8 00 00 00 00 call <foo>
48 89 ec mov rsp,rbp
5d pop rbp
c3 ret
Any stack alignment value larger than 16 results in the unnecessary subtraction
seen above. GCC does not have the same issue.
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
