OpenCL C++: printf becomes mangled c++ symbol, not working with e.g. pocl and llvm-spirv

[davidrohr]

With clang 19.1.3, the following example

__kernel void test()
{
    printf("test");
}

compiles in OpenCL C mode to SPIRV:

clang++ --target=spirv64 -cl-std=CL2.0 -fno-integrated-objemitter -o test.spirv test.cl -O0

but in C++ for OpenCL mode

clang++ --target=spirv64 -cl-std=CLC++2021 -fno-integrated-objemitter -o test.spirv test.cl -O0

I get:

error: 0: Unresolved external reference to "_Z6printfPU3AS2Kcz".
clang++: error: spirv-link command failed with exit code 1 (use -v to see invocation)

(the same happens with -cl-std clc++).

It seems that the LLVM-SPIRV translater expects an unmangled printf symbol, but llvm emits a C++ mangled symbol.
It works when I use the experimental internal SPIRV emiter via -fintegrated-objemitter.

Also with POCL it does not work due to the mangled symbol (see pocl/pocl#1759), thus I assume llvm should produce an unmangled printf symbol as specified in OpenCL 1.2. Or all other software packages will need to adapt for clc++.

[llvmbot]

@llvm/issue-subscribers-opencl

Author: David Rohr (davidrohr)

With clang 19.1.3, the following example ``` __kernel void test() { printf("test"); } ``` compiles in OpenCL C mode to SPIRV: ``` clang++ --target=spirv64 -cl-std=CL2.0 -fno-integrated-objemitter -o test.spirv test.cl -O0 ``` but in C++ for OpenCL mode ``` clang++ --target=spirv64 -cl-std=CLC++2021 -fno-integrated-objemitter -o test.spirv test.cl -O0 ``` I get: ``` error: 0: Unresolved external reference to "_Z6printfPU3AS2Kcz". clang++: error: spirv-link command failed with exit code 1 (use -v to see invocation) ``` (the same happens with `-cl-std clc++`).

It seems that the LLVM-SPIRV translater expects an unmangled printf symbol, but llvm emits a C++ mangled symbol.
It works when I use the experimental internal SPIRV emiter via -fintegrated-objemitter.

Also with POCL it does not work due to the mangled symbol (see pocl/pocl#1759), thus I assume llvm should produce an unmangled printf symbol as specified in OpenCL 1.2. Or all other software packages will need to adapt for clc++.

[svenvh]

I suspect this might be the same issue reported in KhronosGroup/SPIRV-LLVM-Translator#2908 .