[X86] Support cleaning more than 2**16 bytes of stack

The x86 ret instruction has a 16 bit immediate indicating how many bytes
to pop off of the stack beyond the return address.

There is a problem when extremely large structs are passed by value: we
might not be able to fit the number of bytes to pop into the return
instruction.

To fix this, expand RET_FLAG a little later and use a special sequence
to clean the stack:

pop  %ecx     ; return address is now in %ecx
add  $n, %esp ; clean the stack
push %ecx     ; bring the return address back on the stack
ret           ; pop the return address and jmp to it's value

llvm-svn: 262755

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86FloatingPoint.cpp b/llvm/lib/Target/X86/X86FloatingPoint.cpp
index 324c248448e..80cb8679fbe 100644
--- a/llvm/lib/Target/X86/X86FloatingPoint.cpp
+++ b/llvm/lib/Target/X86/X86FloatingPoint.cpp
@@ -1509,6 +1509,7 @@ void FPS::handleSpecialFP(MachineBasicBlock::iterator &Inst) {
     return;
   }
 
+  case X86::RET:
   case X86::RETQ:
   case X86::RETL:
   case X86::RETIL: