https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109567
Bug ID: 109567
Summary: Useless stack adjustment by 16 around calls with odd
stack-argument counts on SysV x86_64
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: pskocik at gmail dot com
Target Milestone: ---
For function calls with odd stack argument counts, gcc generates a useless `sub
$16, %rsp` at the beginning of the calling function.
Example (https://godbolt.org/z/Y4ErE8ee9):
#include <stdio.h>
int callprintf_0stk(char const*Fmt){ return printf(Fmt,0,0,0,0,0),0; }
int callprintf_1stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0, 1),0; }
//useless sub $0x10,%rsp
int callprintf_2stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0, 1,2),0; }
int callprintf_3stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0, 1,2,3),0; }
//useless sub $0x10,%rsp
int callprintf_4stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0, 1,2,3,4),0;
}
int callprintf_5stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0,
1,2,3,4,5),0; } //useless sub $0x10,%rsp
int callprintf_6stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0,
1,2,3,4,5,6),0; }
int callprintf_7stk(char const *Fmt){ return printf(Fmt,0,0,0,0,0,
1,2,3,4,5,6,7),0; } //useless sub $0x10,%rsp
