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[6.40] [core] Avoid a clang vectoriser bug in TColorGradient. #22078

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[6.40] [core] Avoid a clang vectoriser bug in TColorGradient. #22078

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bd55cdf
[core] Disable one loop vectorisation to avoid a clang bug.
hageboeck Apr 24, 2026
e5a6d6f
Revert "Add a script to test #21367."
hageboeck Apr 27, 2026
db3ea4b
Revert "Disable the gl gradient tutorials on mac beta."
hageboeck Apr 27, 2026
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6 changes: 6 additions & 0 deletions core/base/src/TColorGradient.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,12 @@ void TColorGradient::ResetColor(UInt_t nPoints, const Double_t *points,
fColors.assign(colors, colors + nPoints * 4);

Double_t sum[4] = { 0., 0., 0., 0. };
#ifdef __clang__
// Clang vectoriser bug (confirmed for clang 20 - 22)
// https://github.com/llvm/llvm-project/issues/194008
// The store in the loop can smash the stack with e.g. -O2 -mavx2.
#pragma clang loop vectorize(disable)
#endif
for (unsigned n = 0; n < fColors.size(); ++n)
sum[n % 4] += fColors[n];

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19 changes: 0 additions & 19 deletions core/base/test/CMakeLists.txt
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Expand Up @@ -29,25 +29,6 @@ ROOT_ADD_GTEST(CoreSystemTests TSystemTests.cxx LIBRARIES Core)
ROOT_ADD_GTEST(CoreCryptoRandomTest CryptoRandomTest.cxx LIBRARIES Core)

ROOT_ADD_GTEST(CoreColorTests TColorTests.cxx LIBRARIES Core)
if(CMAKE_SYSTEM_NAME MATCHES "Darwin" AND CMAKE_HOST_SYSTEM_VERSION VERSION_GREATER_EQUAL 25.4)
set_tests_properties(gtest-core-base-CoreColorTests PROPERTIES DISABLED True)
file(GENERATE
OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/run_until_failure
CONTENT
"import subprocess
for _ in range(100):
try:
subprocess.run(['$<TARGET_FILE:CoreColorTests>'], check=True)
except subprocess.CalledProcessError as e:
print('This test is expected to fail with a stack corruption: ', e)
exit(123)
print('This test was expected to fail with a stack corruption. Check if it got fixed.')
exit(1)"
TARGET CoreColorTests)

add_test(NAME CoreColor_RunUntilFailure COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/run_until_failure)
set_tests_properties(CoreColor_RunUntilFailure PROPERTIES SKIP_RETURN_CODE 123)
endif()

configure_file(Foo.C Foo.C COPYONLY)
ROOT_ADD_GTEST(IncludePathTest IncludePathTest.cxx LIBRARIES Core)
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7 changes: 0 additions & 7 deletions tutorials/CMakeLists.txt
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Expand Up @@ -739,13 +739,6 @@ foreach(t ${tutorials})
if(${t} IN_LIST multithreaded)
set_tests_properties(tutorial-${tname} PROPERTIES PROCESSORS ${NProcessors})
endif()

if(CMAKE_SYSTEM_NAME MATCHES "Darwin" AND CMAKE_HOST_SYSTEM_VERSION VERSION_GREATER_EQUAL 25.4 AND tname MATCHES "gl-.*grad")
# ROOT-21367
# On mac beta, there is a stack corruption (suspected to be a compiler bug) that may fail these tests
set_tests_properties(tutorial-${tname} PROPERTIES DISABLED True)
message(NOTICE "Disabling tutorial ${tname} for mac beta")
endif()
endforeach()

#---Loop over all MPI tutorials and define the corresponding test---------
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