[PATCH] D28166: Properly merge K&R functions that have attributes

[Richard Smith via Phabricator via cfe-commits]

rsmith added a comment.

The test failure in test/CodeGen/microsoft-call-conv-x64.c definitely indicates a problem. The code has defined behavior, but the IR you say we now produce has undefined behavior due to a type mismatch between the call and the callee.

It looks to me like unprototyped `__stdcall` lowering is broken (prior to your change). Consider:

  void __stdcall g(int n) {}
  void __stdcall (*p)() = g;
  void f() { p(0); }

The types of `p` and `g` are compatible (`g`'s parameter type list does not end in an ellipsis and its parameter type `int` is a promoted type, so it is compatible with an unprototyped function), so the above program is valid, and a call to `f` has defined behavior.

And yet we lower the definition of `g` to `define void @g(i32 %n) ` and the call to

  %0 = load void (...)*, void (...)** @p, align 8
  %callee.knr.cast = bitcast void (...)* %0 to void (i64)*
  call void %callee.knr.cast(i64 0)

... resulting in undefined behavior.


https://reviews.llvm.org/D28166