[SYCL] Add -Wno-sycl-undefined-func-in-image to silence spurious undefined-function warnings by bviyer · Pull Request #23012 · intel/llvm

bviyer · 2026-08-24T21:02:07Z

Silences sycl-post-link's "Undefined function found in " warning. Intended for symbols resolved by the GPU driver / JIT. Adds the SyclUndefinedFuncInImage DiagGroup; the driver forwards suppress-undefined-func-warnings to sycl-post-link.

…unc warnings

srividya-sundaram

Clang Driver changes LGTM. Thanks!

YuriPlyakhin · 2026-08-26T23:02:34Z

I'd prefer to avoid duplicating code or stating the evident in comments.

Suggested change

// Set indirectly by clang's -Wno-sycl-undefined-func-in-image

I think auto-apply just messed things up... :(

YuriPlyakhin · 2026-08-26T23:07:37Z

let's avoid implementation details in the option description, even internal. We may change what we pass from driver, that should not invalidate this internal option.

Suggested change

"in a device image"));

same here - code now looks incorrect.

Co-authored-by: Yury Plyakhin <yury.plyakhin@intel.com>

YuriPlyakhin · 2026-08-26T23:45:44Z

This is the only cl::opt in all of llvm/lib/SYCLPostLink/. The library is intentionally option-free because it's linked into three consumers with different option front-ends: the sycl-post-link tool, clang-linker-wrapper, and sycl-jit. All configuration is passed via PostLinkSettings / ModuleSplitterSettings.

In current implementation, the new flag a silent no-op on the library path. With --offload-new-driver -no-use-sycl-post-link-tool, clang-linker-wrapper runs sycl_post_link::performPostLinkProcessing in-process (ClangLinkerWrapper.cpp:872) using settings built from an ArgList in getSYCLPostLinkSettings (line 645);

--sycl-post-link-options= values are only forwarded to the tool (line 807).

So, in case of library usage the user passes -Wno-..., and still sees the warning.

Please follow the existing pattern instead:

cl::opt<bool> SuppressUndefinedFuncWarnings in llvm/tools/sycl-post-link/sycl-post-link.cpp, next to AllowDeviceImageDependencies.

New field in ModuleSplitterSettings (and PostLinkSettings so it survives the pipeline).

Pass it as a parameter to checkForCallsToUndefinedFunctions / extractCallGraph, exactly like AllowDeviceImageDependencies.

Set it in getSYCLPostLinkSettings from the linker-wrapper's arg list, so the new-offload library path honours it too.

YuriPlyakhin · 2026-08-26T23:57:11Z

@@ -0,0 +1,58 @@
+/// Verify that -W[no-]sycl-undefined-func-in-image is forwarded correctly to


All RUN lines exercise only the legacy offload path. Please add --offload-new-driver test, where the option is serialized differently:

// RUN: %clang -### -fsycl --offload-new-driver -fsycl-targets=spir64 -Wno-sycl-undefined-func-in-image %s 2>&1 \ // RUN: | FileCheck --check-prefix=WNO-NEW %s // WNO-NEW: clang-linker-wrapper{{.*}} "--sycl-post-link-options=-suppress-undefined-func-warnings"

and a matching negative case.

YuriPlyakhin · 2026-08-27T00:02:03Z

+/// sycl-post-link under both the default clang driver and the clang-cl
+/// driver. The clang-cl coverage exists because the underlying Options.td
+/// defs need Visibility<[ClangOption, CLOption]> for the driver's
+/// getLastArg(OPT_Wsycl_..., OPT_Wno_sycl_...) to see the arg under


This is stale after the switch to hasFlag. If possible, could you update the comment with focusing on behavior and avoiding implementation details. Otherwise, the comment might stale again in the future.
Same for other comments in this code, where makes sense.

YuriPlyakhin · 2026-08-27T00:04:36Z

@@ -11506,6 +11492,16 @@ static void getNonTripleBasedSYCLPostLinkOpts(const ToolChain &TC,
  if (allowDeviceImageDependencies(TCArgs))
    addArgs(PostLinkArgs, TCArgs, {"-allow-device-image-dependencies"});

+  // Forward -Wno-sycl-undefined-func-in-image to sycl-post-link. Users pass
+  // this to silence sycl-post-link's "Undefined function ... found in ..."
+  // warning for device-code symbols resolved by the driver/JIT (e.g. Intel


Here and in the rest of the code/comments/docs changed in this PR:
An unqualified "driver" may be read as the clang driver, but here it means the GPU driver.
Please disambiguate: ... for device-code symbols resolved by the GPU runtime or JIT.

YuriPlyakhin · 2026-08-27T00:18:52Z

Appending [-Wsycl-undefined-func-in-image] signals full clang warning semantics, but only the two literal spellings are honoured. -w, -Wno-everything, and -Werror=sycl-undefined-func-in-image all parse cleanly and have no effect.
Maybe we need to be more explicit here: Use -Wno-sycl-undefined-func-in-image to suppress the warning.

YuriPlyakhin · 2026-08-27T00:25:32Z

This takes the test from 2 to 5 full -fsycl -fsycl-link compiles of <sycl/sycl.hpp>.
I suggest keeping the one that adds real end-to-end value (-Wno-... actually suppresses the warning)

Can we drop CHECK-WARNING-REENABLED / CHECK-WARNING-LAST-WNO?

last --W-wins is driver argument handling, already covered by LAST-W/LAST-WNO in clang/test/Driver/sycl-suppress-undefined-func-warnings.cpp.

YuriPlyakhin · 2026-08-27T00:26:54Z

+/// getLastArg(OPT_Wsycl_..., OPT_Wno_sycl_...) to see the arg under
+/// --driver-mode=cl.
+
+// RUN: %clang -### -fsycl -fsycl-targets=spir64 %s 2>&1 \


%clang and %clangxx are redundant for -### forwarding checks since -fsycl implies C++, right?
%clangxx + %clang_cl should be sufficient.

KseniyaTikhomirova

SYCL RT part LGTM

bviyer added 2 commits August 18, 2026 08:56

Stashing my changes for now.

42276af

Add -Wno-sycl-undefined-func-in-image to silence spurious undefined-f…

eebb8b6

…unc warnings

bviyer requested review from a team as code owners August 24, 2026 21:02

bviyer requested a review from KseniyaTikhomirova August 24, 2026 21:02

srividya-sundaram reviewed Aug 25, 2026

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Comment thread clang/include/clang/Basic/DiagnosticGroups.td

srividya-sundaram reviewed Aug 25, 2026

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Comment thread sycl/test/warnings/undefined_functions.cpp Outdated

Added two things mentioned by Srividya and fixed an issue

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bviyer requested a review from srividya-sundaram August 25, 2026 01:16

Fixed clang formatting

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srividya-sundaram approved these changes Aug 25, 2026

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Fixed an issue with the flag

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elizabethandrews reviewed Aug 25, 2026

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Comment thread clang/include/clang/Options/Options.td Outdated

Comment thread clang/include/clang/Basic/DiagnosticGroups.td

mdtoguchi reviewed Aug 25, 2026

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Comment thread clang/include/clang/Options/Options.td Outdated

bviyer requested review from elizabethandrews and mdtoguchi August 25, 2026 16:46

Added Visibility and a test code

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mdtoguchi reviewed Aug 25, 2026

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Comment thread clang/lib/Driver/ToolChains/Clang.cpp Outdated

Fixed issue mentioned by Mike

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elizabethandrews approved these changes Aug 26, 2026

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bviyer requested a review from mdtoguchi August 26, 2026 21:39

Fixed help text

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mdtoguchi approved these changes Aug 26, 2026

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YuriPlyakhin reviewed Aug 26, 2026

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bviyer and others added 2 commits August 26, 2026 18:13

Update llvm/lib/SYCLPostLink/ModuleSplitter.cpp

3258c31

Co-authored-by: Yury Plyakhin <yury.plyakhin@intel.com>

Update llvm/lib/SYCLPostLink/ModuleSplitter.cpp

34f25f7

Co-authored-by: Yury Plyakhin <yury.plyakhin@intel.com>

bviyer requested a review from YuriPlyakhin August 26, 2026 23:15

YuriPlyakhin reviewed Aug 26, 2026

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Comment thread sycl/doc/UsersManual.md

Update sycl/doc/UsersManual.md

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Co-authored-by: Yury Plyakhin <yury.plyakhin@intel.com>

bviyer requested a review from YuriPlyakhin August 26, 2026 23:21

YuriPlyakhin reviewed Aug 26, 2026

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YuriPlyakhin reviewed Aug 27, 2026

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Comment thread clang/include/clang/Basic/DiagnosticGroups.td

YuriPlyakhin reviewed Aug 27, 2026

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Comment thread sycl/doc/UsersManual.md

YuriPlyakhin reviewed Aug 27, 2026

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bviyer requested a review from YuriPlyakhin August 28, 2026 16:24

bviyer added 2 commits August 28, 2026 13:37

Fixed all the issues mentioned by Yury

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Fixed clang formatting

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KseniyaTikhomirova approved these changes Sep 1, 2026

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	// Set indirectly by clang's -Wno-sycl-undefined-func-in-image

		@@ -0,0 +1,58 @@
		/// Verify that -W[no-]sycl-undefined-func-in-image is forwarded correctly to

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