https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116988
Bug ID: 116988
Summary: Documentation for local register variables with
inline-asm could have better example
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: documentation
Severity: enhancement
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Noticed while reading/helping
https://hachyderm.io/@pkhuong@discuss.systems/113255889240859000 .
A few things here.
First off: "Some developers use Local Register Variables in an attempt to
improve gcc’s allocation of registers, especially in large functions. ..." this
should be improved to just say:
"Some developers will try to use Register Variables in an attempt to improve
gcc’s allocation of registers, the problems listed with respect to inline-asm
and calls will cause issues and should not be used".
Second is the example with the inline-asm only has about inputs having issue
but outputs have the same issue too:
so we have:
```
int *t1 = …;
register int *p1 asm ("r0") = …;
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
```
It should be :
```
int *t1 = …;
register int *p1 asm ("r0") = …;
register int *p2 asm ("r1") = t1;
register int *r0 asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
int result = r0;
....
```
