yaxunl added a comment.
In https://reviews.llvm.org/D34342#786941, @bader wrote:
> Added test case reproducing the issue described in the description.
> Removed test cases from test/SemaOpenCL/sampler_t.cl covered by
> test/CodeGenOpenCL/sampler.cl.
>
> While I was moving one test case from test/SemaOpenCL/sampler_t.cl, I found
> another bug in CodeGen library that crashes the compilation if sampler is
> initialized with non-constant expression.
>
> Here is a short reproducer:
>
> int get_sampler_initializer(void);
> kernel void foo() {
> const sampler_t const_smp_func_init = get_sampler_initializer();
> }
>
>
> The problem is that clang does not discard this code as invalid, but CodeGen
> library expects sampler initializer to be a constant expression:
>
> llvm::Value *
> CodeGenModule::createOpenCLIntToSamplerConversion(const Expr *E,
> CodeGenFunction &CGF) {
> llvm::Constant *C = EmitConstantExpr(E, E->getType(), &CGF); // for the
> reproducer expression here is CallExpr.
> auto SamplerT = getOpenCLRuntime().getSamplerType();
> auto FTy = llvm::FunctionType::get(SamplerT, {C->getType()}, false);
> return CGF.Builder.CreateCall(CreateRuntimeFunction(FTy,
> "__translate_sampler_initializer"),
> {C});
> }
>
>
> There are two ways to handle this issue:
>
> 1. Implement diagnostics allowing only compile time constant initializers.
> 2. Add non-constant sampler initializer support to CodeGen library.
>
> OpenCL specification examples give me impression that samplers declared
> inside OpenCL programs must be known at compile time. On the other hand
> OpenCL allows samplers passed via kernel parameters to be unknown at compile
> time.
>
> Thoughts?
The OpenCL spec v1.2 s6.9.b:
The sampler type (sampler_t) can only be used as the type of a function
argument or a
variable declared in the program scope or the outermost scope of a kernel
function. The
behavior of a sampler variable declared in a non-outermost scope of a kernel
function is
implementation-defined. A sampler argument or variable cannot be modified.
The sampler type cannot be used to declare a structure or union field, an array
of
samplers, a pointer to a sampler, or the return type of a function. The sampler
type cannot
be used with the __local and __global address space qualifiers.
So a function returning sampler is invalid. However, the spec does not forbid a
sampler
defined in the outermost scope of a kernel function to be initialized
dynamically, e.g.
kernel void f(sampler_t s1, sampler_t s2, int x) {
sampler_t s = x ? s1 : s2;
}
The question is: if we allow this, will it cause any issue?
https://reviews.llvm.org/D34342
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