From 9a2478ac1a9aafcd5e89808868e170cfdfefcdc1 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Fri, 20 Jan 2012 00:05:46 +0000
Subject: [PATCH] Support MSVC x86-32 sret convention.  PR11688.  Patch by Joe
 Groff.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148513 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86FastISel.cpp     |  3 ++-
 lib/Target/X86/X86ISelLowering.cpp |  9 +++++++--
 test/CodeGen/X86/win32_sret.ll     | 28 ++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 test/CodeGen/X86/win32_sret.ll

diff --git a/lib/Target/X86/X86FastISel.cpp b/lib/Target/X86/X86FastISel.cpp
index bae5ede8d35..13e20f4eb0e 100644
--- a/lib/Target/X86/X86FastISel.cpp
+++ b/lib/Target/X86/X86FastISel.cpp
@@ -1855,7 +1855,8 @@ bool X86FastISel::DoSelectCall(const Instruction *I, const char *MemIntName) {
   // Issue CALLSEQ_END
   unsigned AdjStackUp = TII.getCallFrameDestroyOpcode();
   unsigned NumBytesCallee = 0;
-  if (!Subtarget->is64Bit() && CS.paramHasAttr(1, Attribute::StructRet))
+  if (!Subtarget->is64Bit() && !Subtarget->isTargetWindows() &&
+      CS.paramHasAttr(1, Attribute::StructRet))
     NumBytesCallee = 4;
   BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, TII.get(AdjStackUp))
     .addImm(NumBytes).addImm(NumBytesCallee);
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index b8c0fd60b47..60ecf3f43f6 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -1811,6 +1811,7 @@ X86TargetLowering::LowerFormalArguments(SDValue Chain,
 
   MachineFrameInfo *MFI = MF.getFrameInfo();
   bool Is64Bit = Subtarget->is64Bit();
+  bool IsWindows = Subtarget->isTargetWindows();
   bool IsWin64 = Subtarget->isTargetWin64();
 
   assert(!(isVarArg && IsTailCallConvention(CallConv)) &&
@@ -2046,7 +2047,8 @@ X86TargetLowering::LowerFormalArguments(SDValue Chain,
   } else {
     FuncInfo->setBytesToPopOnReturn(0); // Callee pops nothing.
     // If this is an sret function, the return should pop the hidden pointer.
-    if (!Is64Bit && !IsTailCallConvention(CallConv) && ArgsAreStructReturn(Ins))
+    if (!Is64Bit && !IsTailCallConvention(CallConv) && !IsWindows &&
+        ArgsAreStructReturn(Ins))
       FuncInfo->setBytesToPopOnReturn(4);
   }
 
@@ -2130,6 +2132,7 @@ X86TargetLowering::LowerCall(SDValue Chain, SDValue Callee,
   MachineFunction &MF = DAG.getMachineFunction();
   bool Is64Bit        = Subtarget->is64Bit();
   bool IsWin64        = Subtarget->isTargetWin64();
+  bool IsWindows      = Subtarget->isTargetWindows();
   bool IsStructRet    = CallIsStructReturn(Outs);
   bool IsSibcall      = false;
 
@@ -2543,10 +2546,12 @@ X86TargetLowering::LowerCall(SDValue Chain, SDValue Callee,
   if (X86::isCalleePop(CallConv, Is64Bit, isVarArg,
                        getTargetMachine().Options.GuaranteedTailCallOpt))
     NumBytesForCalleeToPush = NumBytes;    // Callee pops everything
-  else if (!Is64Bit && !IsTailCallConvention(CallConv) && IsStructRet)
+  else if (!Is64Bit && !IsTailCallConvention(CallConv) && !IsWindows &&
+           IsStructRet)
     // If this is a call to a struct-return function, the callee
     // pops the hidden struct pointer, so we have to push it back.
     // This is common for Darwin/X86, Linux & Mingw32 targets.
+    // For MSVC Win32 targets, the caller pops the hidden struct pointer.
     NumBytesForCalleeToPush = 4;
   else
     NumBytesForCalleeToPush = 0;  // Callee pops nothing.
diff --git a/test/CodeGen/X86/win32_sret.ll b/test/CodeGen/X86/win32_sret.ll
new file mode 100644
index 00000000000..878c6db9928
--- /dev/null
+++ b/test/CodeGen/X86/win32_sret.ll
@@ -0,0 +1,28 @@
+; RUN: llc < %s -mtriple=i686-pc-win32 | FileCheck %s -check-prefix=WIN_X32
+; RUN: llc < %s -mtriple=i686-pc-mingw32 | FileCheck %s -check-prefix=MINGW_X32
+; RUN: llc < %s -mtriple=i386-pc-linux | FileCheck %s -check-prefix=LINUX
+; RUN: llc < %s -O0 -mtriple=i686-pc-win32 | FileCheck %s -check-prefix=WIN_X32
+; RUN: llc < %s -O0 -mtriple=i686-pc-mingw32 | FileCheck %s -check-prefix=MINGW_X32
+; RUN: llc < %s -O0 -mtriple=i386-pc-linux | FileCheck %s -check-prefix=LINUX
+
+; The SysV ABI used by most Unixes and Mingw on x86 specifies that an sret pointer
+; is callee-cleanup. However, in MSVC's cdecl calling convention, sret pointer
+; arguments are caller-cleanup like normal arguments.
+
+define void @sret1(i8* sret) nounwind {
+entry:
+; WIN_X32:    {{ret$}}
+; MINGW_X32:  ret $4
+; LINUX:      ret $4
+  ret void
+}
+
+define void @sret2(i32* sret %x, i32 %y) nounwind {
+entry:
+; WIN_X32:    {{ret$}}
+; MINGW_X32:  ret $4
+; LINUX:      ret $4
+  store i32 %y, i32* %x
+  ret void
+}
+
-- 
2.34.1