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[core] Avoid a clang vectoriser bug in TColorGradient.#22060

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hageboeck:loop_vectoriser_bug
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[core] Avoid a clang vectoriser bug in TColorGradient.#22060
hageboeck wants to merge 3 commits intoroot-project:masterfrom
hageboeck:loop_vectoriser_bug

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@hageboeck hageboeck commented Apr 24, 2026

The loop vectoriser in clang-20 to clang-22 can overflow the stack, which should explain the crashes observed when mac beta moved to clang-21.
Here, we instruct the vectoriser to leave the loop in the affected function untouched.

llvm/llvm-project#194008

@hageboeck hageboeck self-assigned this Apr 24, 2026
The loop vectoriser in clang-20 to clang-22 can overflow the stack,
which should explain the crashes observed when mac beta moved to
clang-21.
Here, we instruct the vectoriser to leave the affected loop untouched.

llvm/llvm-project#194008

Fix root-project#21367
This reverts commit 8c25d31.

With the fix for root-project#21367, the test is expected to pass again.
This reverts commit 70ad2cb.

With the fix for root-project#21367, the tests are expected to pass again.
@hageboeck hageboeck force-pushed the loop_vectoriser_bug branch from 132ce99 to 4f3dcc4 Compare April 27, 2026 09:07
@hageboeck hageboeck linked an issue Apr 27, 2026 that may be closed by this pull request
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@hageboeck hageboeck marked this pull request as ready for review April 27, 2026 09:14
@hageboeck hageboeck changed the title [core] Try going around a suspected clang vectoriser bug. [core] Avoid a clang vectoriser bug in TColorGradient. Apr 27, 2026
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Stack corruption in TColorGradient on mac beta

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