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author | Johannes Doerfert <johannes@jdoerfert.de> | 2022-07-13 11:01:54 -0500 |
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committer | Johannes Doerfert <johannes@jdoerfert.de> | 2022-07-21 12:28:45 -0500 |
commit | 7472b42b788e57b7b1ea255aa8670c96cc0aacd8 (patch) | |
tree | ae3d7e9ad9da86ad181d42d0c4a396f4ec7081b6 /openmp | |
parent | a42361dc1c26acae656243232e81a236ba333a8c (diff) | |
download | llvm-7472b42b788e57b7b1ea255aa8670c96cc0aacd8.zip llvm-7472b42b788e57b7b1ea255aa8670c96cc0aacd8.tar.gz llvm-7472b42b788e57b7b1ea255aa8670c96cc0aacd8.tar.bz2 |
[OpenMP] Use Undef instead of null as pointer for inactive lanes
Our conditional writes in the runtime look like this:
```
if (active)
*ptr = value;
```
In the RAII we need to assign `ptr` which comes from a lookup call.
If a thread that is not the main thread calls lookup with the intention
to write the pointer, we'll create a new thread state. As such, we need
to avoid calling lookup for inactive threads. We used to use `nullptr`
as their `ptr` value but that can cause pessimistic reasoning. We now
use `undef` instead.
Differential Revision: https://reviews.llvm.org/D130114
Diffstat (limited to 'openmp')
-rw-r--r-- | openmp/libomptarget/DeviceRTL/include/State.h | 3 | ||||
-rw-r--r-- | openmp/libomptarget/DeviceRTL/include/Utils.h | 7 |
2 files changed, 9 insertions, 1 deletions
diff --git a/openmp/libomptarget/DeviceRTL/include/State.h b/openmp/libomptarget/DeviceRTL/include/State.h index 08f08bd..65d5b6d 100644 --- a/openmp/libomptarget/DeviceRTL/include/State.h +++ b/openmp/libomptarget/DeviceRTL/include/State.h @@ -277,7 +277,8 @@ private: template <typename VTy, typename Ty> struct ValueRAII { ValueRAII(VTy &V, Ty NewValue, Ty OldValue, bool Active, IdentTy *Ident) - : Ptr(Active ? &V.lookup(/* IsReadonly */ false, Ident) : nullptr), + : Ptr(Active ? &V.lookup(/* IsReadonly */ false, Ident) + : (Ty *)utils::UndefPtr), Val(OldValue), Active(Active) { if (!Active) return; diff --git a/openmp/libomptarget/DeviceRTL/include/Utils.h b/openmp/libomptarget/DeviceRTL/include/Utils.h index dc4b1cd..9e71b51 100644 --- a/openmp/libomptarget/DeviceRTL/include/Utils.h +++ b/openmp/libomptarget/DeviceRTL/include/Utils.h @@ -14,6 +14,8 @@ #include "Types.h" +#pragma omp begin declare target device_type(nohost) + namespace _OMP { namespace utils { @@ -72,10 +74,15 @@ template <typename Ty1, typename Ty2> inline Ty1 align_down(Ty1 V, Ty2 Align) { return V - V % Align; } +/// A pointer variable that has by design an `undef` value. Use with care. +__attribute__((loader_uninitialized)) static void *const UndefPtr; + #define OMP_LIKELY(EXPR) __builtin_expect((bool)(EXPR), true) #define OMP_UNLIKELY(EXPR) __builtin_expect((bool)(EXPR), false) } // namespace utils } // namespace _OMP +#pragma omp end declare target + #endif |