[clang] [libc] [llvm] [libc] Implement (v|f)printf on the GPU (PR #96369)

[Jon Chesterfield via cfe-commits]

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@@ -54,7 +54,34 @@ class MockArgList {
   }
 
   template <class T> LIBC_INLINE T next_var() {
-    ++arg_counter;
+    arg_counter++;
+    return T(arg_counter);
+  }
+
+  size_t read_count() const { return arg_counter; }
+};
+
+// Used by the GPU implementation to parse how many bytes need to be read from
+// the variadic argument buffer.
+class DummyArgList {
+  size_t arg_counter = 0;
+
+public:
+  LIBC_INLINE DummyArgList() = default;
+  LIBC_INLINE DummyArgList(va_list) { ; }
+  LIBC_INLINE DummyArgList(DummyArgList &other) {
+    arg_counter = other.arg_counter;
+  }
+  LIBC_INLINE ~DummyArgList() = default;
+
+  LIBC_INLINE DummyArgList &operator=(DummyArgList &rhs) {
+    arg_counter = rhs.arg_counter;
+    return *this;
+  }
+
+  template <class T> LIBC_INLINE T next_var() {
+    arg_counter =
+        ((arg_counter + alignof(T) - 1) / alignof(T)) * alignof(T) + sizeof(T);
     return T(arg_counter);
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JonChesterfield wrote:

maybe split this into separate increment by size and round for the alignment operations. There might be helper functions for the rounding which would be clearer than reading the division / multiplication and trying to pattern match on what alignment code usually looks like (e.g. I expected to see masking off bits so tripped over this)

https://github.com/llvm/llvm-project/pull/96369