From 4e68054b20725f6ec1cac33630258f749fe5debe Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Thu, 13 Oct 2011 08:24:19 +0000
Subject: [PATCH] More closely follow libgcc, which has code after the `ret'
 instruction to release the stack segment and reset the stack pointer. Place
 the code in its own MBB to make the verifier happy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141859 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86FrameLowering.cpp  | 33 ++++++++++++++++++++++------
 test/CodeGen/X86/segmented-stacks.ll |  2 +-
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/lib/Target/X86/X86FrameLowering.cpp b/lib/Target/X86/X86FrameLowering.cpp
index 757cef2d7f7..07e0d0ed263 100644
--- a/lib/Target/X86/X86FrameLowering.cpp
+++ b/lib/Target/X86/X86FrameLowering.cpp
@@ -1336,15 +1336,28 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   if (Is64Bit)
     IsNested = HasNestArgument(&MF);
 
+  // The MOV R10, RAX needs to be in a different block, since the RET we emit in
+  // allocMBB needs to be last (terminating) instruction.
+  MachineBasicBlock *restoreR10MBB = NULL;
+  if (IsNested)
+    restoreR10MBB = MF.CreateMachineBasicBlock();
+
   for (MachineBasicBlock::livein_iterator i = prologueMBB.livein_begin(),
          e = prologueMBB.livein_end(); i != e; i++) {
     allocMBB->addLiveIn(*i);
     checkMBB->addLiveIn(*i);
+
+    if (IsNested)
+      restoreR10MBB->addLiveIn(*i);
+  }
+
+  if (IsNested) {
+    allocMBB->addLiveIn(X86::R10);
+    restoreR10MBB->addLiveIn(X86::RAX);
   }
 
   if (IsNested)
-    allocMBB->addLiveIn(X86::R10);
-
+    MF.push_front(restoreR10MBB);
   MF.push_front(allocMBB);
   MF.push_front(checkMBB);
 
@@ -1414,13 +1427,19 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   if (!Is64Bit)
     BuildMI(allocMBB, DL, TII.get(X86::ADD32ri), X86::ESP).addReg(X86::ESP)
       .addImm(8);
-
-  if (Is64Bit && IsNested)
-    BuildMI(allocMBB, DL, TII.get(X86::MOV64rr), X86::R10).addReg(X86::RAX);
-
   BuildMI(allocMBB, DL, TII.get(X86::RET));
 
-  allocMBB->addSuccessor(&prologueMBB);
+  if (IsNested)
+    BuildMI(restoreR10MBB, DL, TII.get(X86::MOV64rr), X86::R10)
+      .addReg(X86::RAX);
+
+  if (IsNested) {
+    allocMBB->addSuccessor(restoreR10MBB);
+    restoreR10MBB->addSuccessor(&prologueMBB);
+  } else {
+    allocMBB->addSuccessor(&prologueMBB);
+  }
+
   checkMBB->addSuccessor(allocMBB);
   checkMBB->addSuccessor(&prologueMBB);
 
diff --git a/test/CodeGen/X86/segmented-stacks.ll b/test/CodeGen/X86/segmented-stacks.ll
index 37f082c730a..ecdb00d5d1e 100644
--- a/test/CodeGen/X86/segmented-stacks.ll
+++ b/test/CodeGen/X86/segmented-stacks.ll
@@ -81,7 +81,7 @@ define i32 @test_nested(i32 * nest %closure, i32 %other) {
 ; X64-NEXT: movabsq $0, %r10
 ; X64-NEXT: movabsq $0, %r11
 ; X64-NEXT: callq __morestack
-; X64-NEXT: movq %rax, %r10
 ; X64-NEXT: ret
+; X64:      movq %rax, %r10
 
 }