[OpenCL] Reduce emitting candidate notes for builtins

[svenvh]

Summary

When overload resolution fails, clang emits a note diagnostic for each
candidate. For OpenCL builtins this often leads to many repeated note
diagnostics with no new information. Stop emitting such notes.

Update a test that was relying on counting those notes to check how
many builtins are available for certain extension configurations.

[Anastasia]

clang/lib/Sema/SemaOverload.cpp

11272

It would have been nice to print each of those overloads but my guess is that it's too much work?

[svenvh]

clang/lib/Sema/SemaOverload.cpp

11272

It's not trivial to print those overloads because we don't have a real source declaration, but even if it was trivial I am not sure if there is much value in printing all overloads. Typically there are a lot of overloads for OpenCL builtins, partly because of all the vector versions. I don't think a user will get much value out of screens full of overloads that didn't match.

For example, for the following code

int i, j, k;
i = max(i, j, k);

without this patch clang produces 121 note diagnostics. If we manage to fit the diagnostic and candidate on a single line (which I doubt we can, normally they take 3 lines each), a user will still have to scroll through a few screens (on a 50-line terminal) of note diagnostics before reaching the actual error diagnostic.

[Anastasia]

LGTM! Thanks

clang/lib/Sema/SemaOverload.cpp

 static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
                                   unsigned NumArgs,
                                   bool TakingCandidateAddress,
                                   LangAS CtorDestAS = LangAS::Default) {
   FunctionDecl *Fn = Cand->Function;
   if (shouldSkipNotingLambdaConversionDecl(Fn))
     return;
 
+  // There is no physical candidate declaration to point to for OpenCL builtins.
+  // Except for failed conversions, the notes are identical for each candidate,
+  // so do not generate such notes.
+  if (S.getLangOpts().OpenCL && Fn->isImplicit() &&
+      Cand->FailureKind != ovl_fail_bad_conversion)
+    return;
+
   // Note deleted candidates, but only if they're viable.
   if (Cand->Viable) {
     if (Fn->isDeleted()) {
       std::string FnDesc;
       std::pair<OverloadCandidateKind, OverloadCandidateSelect> FnKindPair =
           ClassifyOverloadCandidate(S, Cand->FoundDecl, Fn,
                                     Cand->getRewriteKind(), FnDesc);
 

clang/test/SemaOpenCL/fdeclare-opencl-builtins.cl

 #endif // !defined(NO_HEADER) && __OPENCL_C_VERSION__ >= 200
 
 #if !defined(NO_HEADER) && __OPENCL_C_VERSION__ == 200 && defined(__opencl_c_generic_address_space)
 
 // Test that overloads that use atomic_double are not available when the fp64
 // extension is disabled.  Test this by counting the number of notes about
 // candidate functions.
 void test_atomic_double_reporting(volatile __generic atomic_int *a) {
-  atomic_init(a);
+  atomic_init(a, a);
   // expected-error@-1{{no matching function for call to 'atomic_init'}}
 #if defined(NO_FP64)
   // Expecting 5 candidates: int, uint, long, ulong, float
-  // expected-note@-4 5 {{candidate function not viable: requires 2 arguments, but 1 was provided}}
+  // expected-note@-4 5 {{candidate function not viable: no known conversion}}
 #else
   // Expecting 6 candidates: int, uint, long, ulong, float, double
-  // expected-note@-7 6 {{candidate function not viable: requires 2 arguments, but 1 was provided}}
+  // expected-note@-7 6 {{candidate function not viable: no known conversion}}
 #endif
 }
 
 #endif
 
 #if defined(NO_ATOMSCOPE) && __OPENCL_C_VERSION__ >= 300
 // Disable the feature by undefining the feature macro.
 #undef __opencl_c_atomic_scope_device
 
 // Test that only the overload with explicit order and scope arguments is
 // available when the __opencl_c_atomic_scope_device feature is disabled.
 void test_atomics_without_scope_device(volatile __generic atomic_int *a_int) {
   int d;
 
   atomic_exchange(a_int, d);
   // expected-error@-1{{use of undeclared identifier 'atomic_exchange'}}
 
   atomic_exchange_explicit(a_int, d, memory_order_seq_cst);
   // expected-error@-1{{no matching function for call to 'atomic_exchange_explicit'}}
-  // expected-note@-2 + {{candidate function not viable}}
 
   atomic_exchange_explicit(a_int, d, memory_order_seq_cst, memory_scope_work_group);
 }
 
 #endif
 
 // Test old atomic overloaded with generic address space in C++ for OpenCL.
 #if __OPENCL_C_VERSION__ >= 200
kernel void basic_image_readonly(read_only image2d_t image_read_only_image2d) {
   sampler_t sampler;
   half4 res;
   float4 resf;
 
   resf = read_imagef(image_read_only_image2d, i2);
   res = read_imageh(image_read_only_image2d, i2);
 #if __OPENCL_C_VERSION__ < CL_VERSION_1_2 && !defined(__OPENCL_CPP_VERSION__)
   // expected-error@-3{{no matching function for call to 'read_imagef'}}
-  // expected-note@-4 + {{candidate function not viable}}
-  // expected-error@-4{{no matching function for call to 'read_imageh'}}
-  // expected-note@-5 + {{candidate function not viable}}
+  // expected-error@-3{{no matching function for call to 'read_imageh'}}
 #endif
   res = read_imageh(image_read_only_image2d, sampler, i2);
 
   int imgWidth = get_image_width(image_read_only_image2d);
 }
 
 #if __OPENCL_C_VERSION__ >= CL_VERSION_2_0
 kernel void basic_image_readwrite(read_write image3d_t image_read_write_image3d) {
kernel void basic_image_writeonly(write_only image1d_buffer_t image_write_only_image1d_buffer, write_only image3d_t image3dwo) {
 
   write_imagef(image_write_only_image1d_buffer, i, f4);
   write_imageh(image_write_only_image1d_buffer, i, h4);
 
   int4 i4;
   write_imagef(image3dwo, i4, i, f4);
 #if __OPENCL_C_VERSION__ <= CL_VERSION_1_2 && !defined(__OPENCL_CPP_VERSION__)
   // expected-error@-2{{no matching function for call to 'write_imagef'}}
-  // expected-note@-3 + {{candidate function not viable}}
 #endif
 }
 
 kernel void basic_subgroup(global uint *out) {
   out[0] = get_sub_group_size();
 #if __OPENCL_C_VERSION__ <= CL_VERSION_1_2 && !defined(__OPENCL_CPP_VERSION__)
   // expected-error@-2{{use of undeclared identifier 'get_sub_group_size'}}
 #endif