[LLVMbugs] [Bug 20278] New: MS ABI: fastcall methods with struct return are broken

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20278

            Bug ID: 20278
           Summary: MS ABI: fastcall methods with struct return are broken
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rnk at google.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

We have two register parameters and we are failing to account for the fact that
the sret parameter consumes one register slot.

This program fails to link and run together with MSVC:
struct SRet {
  int x;
  SRet(int x) : x(x) {}
};
struct A {
  virtual SRet __fastcall f(int);
};
#ifdef CONFIG_1
SRet A::f(int x) {
  return SRet(x);
}
#else
int main() {
  A a;
  SRet x = a.f(42);
  return x.x;
}
#endif

It should exit 42.

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