Messages in this thread | | | From | cgel.zte@gmail ... | Subject | 'Re: [PATCH] drivers/android: remove redundant ret variable' | Date | Wed, 5 Jan 2022 09:19:42 +0000 |
| |
I found that there are indeed some optimizations after removing the redundancy.
For example:
int foo(int a, int b) { int ret; ret = a>b ? a: b; return ret; } int main() { int val; val = foo(7,2); return 0; }
and
int foo(int a, int b) { return a>b ? a: b; } int main() { int val; val = foo(7,2); return 0; }
The corresponding disassembly code is as follows:
1129: f3 0f 1e fa endbr64 112d: 55 push %rbp 112e: 48 89 e5 mov %rsp,%rbp 1131: 89 7d fc mov %edi,-0x4(%rbp) 1134: 89 75 f8 mov %esi,-0x8(%rbp) 1137: 8b 45 fc mov -0x4(%rbp),%eax 113a: 39 45 f8 cmp %eax,-0x8(%rbp) 113d: 0f 4d 45 f8 cmovge -0x8(%rbp),%eax 1141: 5d pop %rbp 1142: c3 retq
and
1129: f3 0f 1e fa endbr64 112d: 55 push %rbp 112e: 48 89 e5 mov %rsp,%rbp 1131: 89 7d ec mov %edi,-0x14(%rbp) 1134: 89 75 e8 mov %esi,-0x18(%rbp) 1137: 8b 45 ec mov -0x14(%rbp),%eax 113a: 39 45 e8 cmp %eax,-0x18(%rbp) 113d: 0f 4d 45 e8 cmovge -0x18(%rbp),%eax 1141: 89 45 fc mov %eax,-0x4(%rbp) 1144: 8b 45 fc mov -0x4(%rbp),%eax 1147: 5d pop %rbp 1148: c3 retq
After removing the redundancy, the compiler does have some optimizations
| |