https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118467
Bug ID: 118467
Summary: Missed pointer overflow optimisation
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: sjames at gcc dot gnu.org
Target Milestone: ---
Created attachment 60148
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=60148&action=edit
mbrtowc.c.xz
This comes from
https://inbox.sourceware.org/libc-alpha/20250114014804.79188-1-yunqi...@isrc.iscas.ac.cn/T/#u
which is the same as PR82694.
```
$ gcc mbrtowc.c -std=gnu11 -fgnu89-inline -O2 -fPIE -ftls-model=initial-exec
-fmerge-all-constants -frounding-math -fno-stack-protector -fmath-errno -c
-ggdb3
[...]
$ objdump -S mbrtowc.o
[...]
inbuf = (const unsigned char *)s;
endbuf = inbuf + n;
if (__builtin_expect((endbuf < inbuf), 0)) {
7d: 48 01 d8 add %rbx,%rax
inbuf = (const unsigned char *)s;
80: 48 89 5c 24 28 mov %rbx,0x28(%rsp)
if (__builtin_expect((endbuf < inbuf), 0)) {
85: 4c 8d 4c 24 20 lea 0x20(%rsp),%r9
8a: 48 89 c1 mov %rax,%rcx
8d: 0f 82 a5 00 00 00 jb 138 <__mbrtowc+0x138>
endbuf = (const unsigned char *)~(uintptr_t)0;
if (endbuf == inbuf)
```
We don't seem to optimise the comparison of endbuf/inbuf away.
