[ms-cxxabi] Add a new calling convention that swaps 'this' and 'sret'

MSVC always places the 'this' parameter for a method first.  The
implicit 'sret' pointer for methods always comes second.  We already
implement this for __thiscall by putting sret parameters on the stack,
but __cdecl methods require putting both parameters on the stack in
opposite order.

Using a special calling convention allows frontends to keep the sret
parameter first, which avoids breaking lots of assumptions in LLVM and
Clang.

Fixes PR15768 with the corresponding change in Clang.

Reviewers: ributzka, majnemer

Differential Revision: http://llvm-reviews.chandlerc.com/D2663

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200561 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 69 insertions, 0 deletions

diff --git a/test/CodeGen/X86/cdecl-method-return.ll b/test/CodeGen/X86/cdecl-method-return.ll
new file mode 100644
index 0000000000..e7af59737e
--- /dev/null
+++ b/test/CodeGen/X86/cdecl-method-return.ll
@@ -0,0 +1,69 @@
+; RUN: llc < %s -mtriple=i686-pc-win32 | FileCheck %s
+
+; The sret flag causes the first two parameters to be reordered on the stack.
+
+define x86_cdeclmethodcc void @foo(i32* sret %dst, i32* %src) {
+  %v = load i32* %src
+  store i32 %v, i32* %dst
+  ret void
+}
+
+; CHECK-LABEL: _foo:
+; CHECK:  movl    8(%esp), %[[dst:[^ ]*]]
+; CHECK:  movl    4(%esp), %[[src:[^ ]*]]
+; CHECK:  movl    (%[[src]]), %[[v:[^ ]*]]
+; CHECK:  movl    %[[v]], (%[[dst]])
+; CHECK:  retl
+
+define i32 @bar() {
+  %src = alloca i32
+  %dst = alloca i32
+  store i32 42, i32* %src
+  call x86_cdeclmethodcc void @foo(i32* sret %dst, i32* %src)
+  %v = load i32* %dst
+  ret i32 %v
+}
+
+; CHECK-LABEL: _bar:
+; CHECK:  movl    $42, [[src:[^,]*]]
+; CHECK:  leal    [[src]], %[[reg:[^ ]*]]
+; CHECK:  movl    %[[reg]], (%esp)
+; CHECK:  leal    [[dst:[^,]*]], %[[reg:[^ ]*]]
+; CHECK:  movl    %[[reg]], 4(%esp)
+; CHECK:  calll   _foo
+; CHECK:  movl    [[dst]], %eax
+; CHECK:  retl
+
+; If we don't have the sret flag, parameters are not reordered.
+
+define x86_cdeclmethodcc void @baz(i32* %dst, i32* %src) {
+  %v = load i32* %src
+  store i32 %v, i32* %dst
+  ret void
+}
+
+; CHECK-LABEL: _baz:
+; CHECK:  movl    4(%esp), %[[dst:[^ ]*]]
+; CHECK:  movl    8(%esp), %[[src:[^ ]*]]
+; CHECK:  movl    (%[[src]]), %[[v:[^ ]*]]
+; CHECK:  movl    %[[v]], (%[[dst]])
+; CHECK:  retl
+
+define i32 @qux() {
+  %src = alloca i32
+  %dst = alloca i32
+  store i32 42, i32* %src
+  call x86_cdeclmethodcc void @baz(i32* %dst, i32* %src)
+  %v = load i32* %dst
+  ret i32 %v
+}
+
+; CHECK-LABEL: _qux:
+; CHECK:  movl    $42, [[src:[^,]*]]
+; CHECK:  leal    [[src]], %[[reg:[^ ]*]]
+; CHECK:  movl    %[[reg]], 4(%esp)
+; CHECK:  leal    [[dst:[^,]*]], %[[reg:[^ ]*]]
+; CHECK:  movl    %[[reg]], (%esp)
+; CHECK:  calll   _baz
+; CHECK:  movl    [[dst]], %eax
+; CHECK:  retl