[clang] [llvm] [AMDGPU] Enable OpenCL hostcall printf (WIP) (PR #72556)

[Vikram Hegde via cfe-commits]

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@@ -3616,6 +3617,12 @@ unsigned FunctionDecl::getBuiltinID(bool ConsiderWrapperFunctions) const {
   if (!ConsiderWrapperFunctions && getStorageClass() == SC_Static)
     return 0;
 
+  // AMDGCN implementation supports printf as a builtin
+  // for OpenCL
+  if (Context.getTargetInfo().getTriple().isAMDGCN() &&
+      Context.getLangOpts().OpenCL && BuiltinID == AMDGPU::BIprintf)
+    return BuiltinID;
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vikramRH wrote:

@arsenm, thanks for the info. CustomTypeChecking is a valid option. I'm not sure why OpenCL community did not consider this change despite OpenCL specs specifying the details. I could create a separate patch for this (probably folks from OCL community would provide further background). Meanwhile, can this go ahead as an AMDGPU specific workaround for now so that we have the intended feature in place ? (The frontend changes here can be reverted with that follow up patch )

PS :Also, I see another issue . OpenCL v1.2 s6.9.f states none of the functions defined in C99 headers are available. This would mean std printf is supposed to be treated differently than OpenCL builtins and consequently the builtin IDs assigned to them "need" to be different. If this understanding is correct, moving ahead with using same builtin ID as std printf is not the right way.

https://github.com/llvm/llvm-project/pull/72556