[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, 22 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/x86-big-ret.ll b/llvm/test/CodeGen/X86/x86-big-ret.ll
new file mode 100644
index 00000000000..b7fed33f396
--- /dev/null
+++ b/llvm/test/CodeGen/X86/x86-big-ret.ll
@@ -0,0 +1,22 @@
+; RUN: llc < %s | FileCheck %s
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i386-pc-windows-msvc"
+
+define x86_fastcallcc i32 @test1(i32 inreg %V, [65533 x i8]* byval %p_arg) {
+  ret i32 %V
+}
+; CHECK-LABEL: @test1@65540:
+; CHECK:      movl %ecx, %eax
+; CHECK-NEXT: popl %ecx
+; CHECK-NEXT: addl $65536, %esp
+; CHECK-NEXT: pushl %ecx
+; CHECK-NEXT: retl
+
+define x86_stdcallcc void @test2([65533 x i8]* byval %p_arg) {
+  ret void
+}
+; CHECK-LABEL: _test2@65536:
+; CHECK:      popl %ecx
+; CHECK-NEXT: addl $65536, %esp
+; CHECK-NEXT: pushl %ecx
+; CHECK-NEXT: retl