Count the sret register as well when keeping track of how many integer registers are available for extern(C) functions on x86-64. Interestingly, llvm-g++ seems to have a very similar bug: http://llvm.org/pr4242 (So this breaks ABI-compatibility with llvm-gcc for this corner case, but gains it with gcc...) To clarify, this is about code like this: {{{ struct S { void*[3] data; } struct T { void*[2] data; } // The T should be passed in memory, and p in the last int register. extern(C) S fail(int, int, int, int, T t, void* p) { S s; s.data[0] = t.data[0]; s.data[1] = t.data[1]; s.data[2] = p; return s; } }}} which should generate code functionally equivalent to this: {{{ extern(C) S* succeed(S* s, int, int, int, int, T t, void* p) { s.data[0] = t.data[0]; s.data[1] = t.data[1]; s.data[2] = p; return s; } }}} (with the same definitions for S and T)

// this head contains stuff used by all the IR

#ifndef LDC_IR_IR_H
#define LDC_IR_IR_H

#include <deque>

#include "ir/irforw.h"
#include "root.h"

struct IRState;
struct IrFunction;

struct IrBase : Object
{
    virtual ~IrBase() {}
};

class Ir
{
public:
    Ir();

    void setState(IRState* p)   { irs = p; }
    IRState* getState()         { return irs; }

    void addFunctionBody(IrFunction* f);
    void emitFunctionBodies();

private:
    IRState* irs;

    std::deque<IrFunction*> functionbodies;
};

#endif