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[offload] Remove bad assert in StaticLoopChunker::Distribute #132705

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Merged
merged 1 commit into from
Mar 28, 2025
Merged

[offload] Remove bad assert in StaticLoopChunker::Distribute #132705

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1 change: 0 additions & 1 deletion offload/DeviceRTL/src/Workshare.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -820,7 +820,6 @@ template <typename Ty> class StaticLoopChunker {
Ty ThreadChunk = 0;
Ty NumThreads = 1;
Ty TId = 0;
ASSERT(TId == mapping::getThreadIdInBlock(), "Bad thread id");
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The three lines of code above assume this should be the case.

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So this code is only ever expected to run with thread zero? That seems wrong because I thought even in generic mode we used a warp at the end of the block or something.

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Yes, but in the last warp we only use one thread instead of all of them.

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But this asserts that only thread zero will ever execute here.

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I think we need @DominikAdamski to provide some insight into this code. I can only comment based on empirical experience, with the assumption that flang is generating correct calls into the runtime.

FWIW, this code (i.e. __kmpc_distribute_static_loop*) does not seem to be used by clang.


// All teams need to participate.
Ty NumBlocks = mapping::getNumberOfBlocksInKernel();
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26 changes: 26 additions & 0 deletions offload/test/offloading/fortran/target-teams-dist-nest-par.f90
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@@ -0,0 +1,26 @@
! REQUIRES: flang, amdgpu

! RUN: %libomptarget-compile-fortran-generic
! RUN: %libomptarget-run-generic 2>&1 | %fcheck-generic
program main
integer :: array(10) = 0
integer :: x, y, z
!$omp target
!$omp teams distribute private(x, y)
OuterLoopOne: do x=1,1
array(2) = 42
OuterLoopTwo: do y=1,1
!$omp parallel do private(z)
InnerLoopOne: do z=1,10
array(z) = 20
enddo InnerLoopOne
!$omp end parallel do
enddo OuterLoopTwo
enddo OuterLoopOne
!$omp end teams distribute
!$omp end target
! Expected to print all 20's
print *, array
end program main

! CHECK: 20 20 20 20 20 20 20 20 20 20