| Issue |
176408
|
| Summary |
[MachinePipeliner] Generate invalid schedule due to incorrect memory instructions reordering
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
kasuga-fj
|
The following Fortran program produces incorrect output when MachinePipeliner is enabled.
```fortran
program main
integer,parameter :: n = 10
real a(n),b(n),c(n)
do i=1,n
a(i)=1.0
b(i)=4.0
c(i)=1.0
end do
call sub(n,a,b,c,4.0)
write(6,*) c
stop
end program main
subroutine sub(n,a,b,c,x)
integer n
real a(n),b(n),c(n),x,s
do i=2,n
s = a(i) + sqrt(b(i))
a(i) = a(i-1) + x
c(i) = a(i) + s
end do
end subroutine
```
```sh
$ flang -v
flang version 22.0.0git (https://github.com/llvm/llvm-project.git 2f7e218017db69454ea84e1849fcb9a11b1f7fef)
...
# Without pipeliner
$ flang -O3 -mcpu=neoverse-v1 -fno-unroll-loops a.f90
$ ./a.out
1. 8. 12. 16. 20. 24. 28. 32. 36. 40.
Fortran STOP
# With pipeliner
$ flang -O3 -mcpu=neoverse-v1 -fno-unroll-loops -mllvm -aarch64-enable-pipeliner a.f90
$ ./a.out
1. 8. 12. 28. 36. 44. 52. 60. 68. 40.
Fortran STOP
```
See https://godbolt.org/z/943W3ch6d for the reduced reproducer and debug output. Apparently, in the subroutine `sub`, the order of `SU(5)` (the load from `a(i)`) and `SU(10)` (the store to `a(i)`) is swapped incorrectly.
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