https://bugs.llvm.org/show_bug.cgi?id=46450
Bug ID: 46450
Summary: More registers are used when multiple target regions
are compiled together
Product: OpenMP
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Clang Compiler Support
Assignee: unassignedclangb...@nondot.org
Reporter: xw111lu...@gmail.com
CC: llvm-bugs@lists.llvm.org
I initially spotted this issue with AOMP but it seems from upstream clang.
https://github.com/ROCm-Developer-Tools/aomp/issues/24
reproducer:
git clone https://github.com/ye-luo/miniqmc
cd miniqmc/build
cmake -DCMAKE_CXX_COMPILER=clang++ -DENABLE_OFFLOAD=ON \
-DUSE_OBJECT_TARGET=ON -DCMAKE_EXE_LINKER_FLAGS="-v" ..
make -j32 check_spo_batched
all the 6 kernels use 254 registers.
Then I comment out "target teams" at 159, 311, 405.
make -j32 check_spo_batched
now all the 3 kernels left use 243 registers.
If I add
-DCMAKE_CXX_FLAGS="-Xcuda-ptxas -v" to cmake and print out register usage
reported by ptxas. The three kernels take 146, 30, 30 registers when compiled.
I think the register usage is fine when kernels are compiled individually.
Somehow at linking, all the assembled kernels get the worst register usage
among all the individual kernels.
It destroys performance completely.
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