argument. The x86-64 ABI requires the incoming value of %rdi to
be copied to %rax on exit from a function that is returning a
large C struct.

Also, add a README-X86-64 entry detailing the missed optimization
opportunity and proposing an alternative approach.

llvm-svn: 50075

llvm-svn: 45605

llvm-svn: 45418

enabled by passing -tailcallopt to llc.  The optimization is
performed if the following conditions are satisfied:
* caller/callee are fastcc
* elf/pic is disabled OR
  elf/pic enabled + callee is in module + callee has
  visibility protected or hidden

llvm-svn: 42870

hard to catch bugs with retaddr lowering

llvm-svn: 41104

llvm-svn: 39967

it is defined in.

llvm-svn: 36196

llvm-svn: 30608

llvm-svn: 30549

llvm-svn: 28737

function that is being lowered is forced to use FP. Currently this is only
true for main() / Cygwin.

llvm-svn: 28703