https://bugs.llvm.org/show_bug.cgi?id=51701
Bug ID: 51701
Summary: [OpenMP 4.5] ORDERED SIMD construct in loop SIMD
doesn't work as required by the specification
Product: clang
Version: 10.0
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: OpenMP
Assignee: unassignedclangb...@nondot.org
Reporter: shiwei...@compiler-dev.com
CC: llvm-bugs@lists.llvm.org
For the following code:
```c
#include <stdio.h>
void work(int j) {
int i;
#pragma omp parallel
#pragma omp for simd ordered
for (i = 1; i <= 10; i++) {
printf("%d\n", i);
#pragma omp ordered simd threads
{
printf("%d\n", i * j + 100000);
}
}
}
int main() {
int k = 13;
work(k);
}
```
GCC (Ubuntu 9.3.0-11ubuntu0~18.04.1) will generate an executable which prints
something like:
```
9
7
4
5
2
3
1
100013
100026
100039
10
6
8
100052
100065
100078
100091
100104
100117
100130
```
And this output is in line with what is required by the specification (OpenMP
API v4.5): the block demarcated by an ORDERED SIMD construct in a "simd, or
loop SIMD region [..] will be exectued in the order of the loop iterations".
But the executable generated by clang will print something like:
```
1
100013
4
100052
5
100065
7
100091
6
100078
2
100026
3
100039
8
100104
10
100130
9
100117
```
For another piece of code (using ORDERED SIMD in a SIMD region, not in a loop
SIMD region):
```c
#include <stdio.h>
void work(int j) {
int i;
#pragma omp simd
for (i = 1; i <= 10; i++) {
printf("%d\n", i);
#pragma omp ordered simd
{
printf("%d\n", i * j + 100000);
}
}
}
int main() {
int k = 13;
work(k);
}
```
Both sides will output:
```
1
100013
2
100026
3
100039
4
100052
5
100065
6
100078
7
100091
8
100104
9
100117
10
```
which is correct according to the specification.
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