From 21a9fd247ef20f03f6ac8d61daa20d44e39c11b5 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Tue, 3 Dec 2013 20:51:23 +0000
Subject: [PATCH] Fix mingw32 thiscall + sret.

Unlike msvc, when handling a thiscall + sret gcc will
* Put the sret in %ecx
* Put the this pointer is (%esp)

This fixes, for example, calling stringstream::str.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196312 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86CallingConv.td | 26 +++++++++++++++++++++-----
 test/CodeGen/X86/win32_sret.ll   | 28 ++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/lib/Target/X86/X86CallingConv.td b/lib/Target/X86/X86CallingConv.td
index a78b5c0a796..fdc1140d596 100644
--- a/lib/Target/X86/X86CallingConv.td
+++ b/lib/Target/X86/X86CallingConv.td
@@ -453,18 +453,34 @@ def CC_X86_32_FastCall : CallingConv<[
   CCDelegateTo<CC_X86_32_Common>
 ]>;
 
-def CC_X86_32_ThisCall : CallingConv<[
+def CC_X86_32_ThisCall_Common : CallingConv<[
+  // The first integer argument is passed in ECX
+  CCIfType<[i32], CCAssignToReg<[ECX]>>,
+
+  // Otherwise, same as everything else.
+  CCDelegateTo<CC_X86_32_Common>
+]>;
+
+def CC_X86_32_ThisCall_Mingw : CallingConv<[
+  // Promote i8/i16 arguments to i32.
+  CCIfType<[i8, i16], CCPromoteToType<i32>>,
+
+  CCDelegateTo<CC_X86_32_ThisCall_Common>
+]>;
+
+def CC_X86_32_ThisCall_Win : CallingConv<[
   // Promote i8/i16 arguments to i32.
   CCIfType<[i8, i16], CCPromoteToType<i32>>,
 
   // Pass sret arguments indirectly through stack.
   CCIfSRet<CCAssignToStack<4, 4>>,
 
-  // The first integer argument is passed in ECX
-  CCIfType<[i32], CCAssignToReg<[ECX]>>,
+  CCDelegateTo<CC_X86_32_ThisCall_Common>
+]>;
 
-  // Otherwise, same as everything else.
-  CCDelegateTo<CC_X86_32_Common>
+def CC_X86_32_ThisCall : CallingConv<[
+  CCIfSubtarget<"isTargetCygMing()", CCDelegateTo<CC_X86_32_ThisCall_Mingw>>,
+  CCDelegateTo<CC_X86_32_ThisCall_Win>
 ]>;
 
 def CC_X86_32_FastCC : CallingConv<[
diff --git a/test/CodeGen/X86/win32_sret.ll b/test/CodeGen/X86/win32_sret.ll
index a24963a3f34..002cac88245 100644
--- a/test/CodeGen/X86/win32_sret.ll
+++ b/test/CodeGen/X86/win32_sret.ll
@@ -124,3 +124,31 @@ entry:
 ; WIN32:      ret
   ret void
 }
+
+
+%struct.test6 = type { i32, i32, i32 }
+define void @test6_f(%struct.test6* %x) nounwind {
+; WIN32-LABEL: _test6_f:
+; MINGW_X86-LABEL: _test6_f:
+
+; The %x argument is moved to %ecx. It will be the this pointer.
+; WIN32: movl    8(%ebp), %ecx
+
+; The %x argument is moved to (%esp). It will be the this pointer. With -O0
+; we copy esp to ecx and use (ecx) instead of (esp).
+; MINGW_X86: movl    8(%ebp), %eax
+; MINGW_X86: movl    %eax, (%e{{([a-d]x)|(sp)}})
+
+; The sret pointer is (%esp)
+; WIN32:          leal    8(%esp), %[[REG:e[a-d]x]]
+; WIN32-NEXT:     movl    %[[REG]], (%e{{([a-d]x)|(sp)}})
+
+; The sret pointer is %ecx
+; MINGW_X86-NEXT: leal    8(%esp), %ecx
+; MINGW_X86-NEXT: calll   _test6_g
+
+  %tmp = alloca %struct.test6, align 4
+  call x86_thiscallcc void @test6_g(%struct.test6* sret %tmp, %struct.test6* %x)
+  ret void
+}
+declare x86_thiscallcc void @test6_g(%struct.test6* sret, %struct.test6*)