[llvm] [SPIR-V] Don't lower builtin variadic functions (PR #188517)

[Dmitry Sidorov via llvm-commits]

================
@@ -984,6 +993,29 @@ struct SPIRV final : public VariadicABIInfo {
     return {A, false};
   }
 
+  // The SPIR-V backend has special handling for builtins.
+  bool ignoreFunction(Function *F) override {
+    if (!F->isDeclaration())
+      return false;
+
+    StringRef Name = F->getName();
+
+    // Skip any SPIR-V builtins.
+    if (Name.contains("__spirv_"))
+      return true;
+
+    // Skip the builtin printf function.
+    if (Name.contains("printf")) {
+      std::string Demangled = llvm::demangle(Name.str());
+      // Demangled name will be "printf(...)" for the builtin, "printf" for
+      // unmangled extern "C", or "namespace::printf(...)" for namespaced.
+      if (StringRef(Demangled).starts_with("printf(") || Demangled == "printf")
+        return true;
+    }
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MrSidims wrote:

I must say, I'm not a biggest fun of doing check with contains, but guess making SPIR-V backend flow smarter regarding builtins detection goes outside of the scope of this patch.

https://github.com/llvm/llvm-project/pull/188517