From c26c03d911f8f686aabc19705ef2f240098cc886 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans@hanshq.net>
Date: Wed, 5 Oct 2016 15:39:27 +0000
Subject: [PATCH] Revert r282920 "X86: Allow conditional tail calls in Win64
 "leaf" functions (PR26302)"

This is suspected to cause a miscompile in Chromium. Reverting while
investigating.

llvm-svn: 283329
---
 llvm/lib/Target/X86/X86ExpandPseudo.cpp       |  5 ++---
 llvm/lib/Target/X86/X86InstrInfo.cpp          |  7 ++++---
 llvm/test/CodeGen/X86/conditional-tailcall.ll | 27 ++-------------------------
 3 files changed, 8 insertions(+), 31 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ExpandPseudo.cpp b/llvm/lib/Target/X86/X86ExpandPseudo.cpp
index c945c02..192b942 100644
--- a/llvm/lib/Target/X86/X86ExpandPseudo.cpp
+++ b/llvm/lib/Target/X86/X86ExpandPseudo.cpp
@@ -122,9 +122,8 @@ bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
         Op = X86::TAILJMPd_CC;
         break;
       case X86::TCRETURNdi64cc:
-        assert(!MBB.getParent()->hasWinCFI() &&
-               "Conditional tail calls confuse "
-               "the Win64 unwinder.");
+        assert(!IsWin64 && "Conditional tail calls confuse the Win64 unwinder.");
+        // TODO: We could do it for Win64 "leaf" functions though; PR30337.
         Op = X86::TAILJMPd64_CC;
         break;
       default:
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 11fe9d3..20dab29 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -4277,9 +4277,9 @@ bool X86InstrInfo::canMakeTailCallConditional(
     return false;
   }
 
-  const MachineFunction *MF = TailCall.getParent()->getParent();
-  if (Subtarget.isTargetWin64() && MF->hasWinCFI()) {
+  if (Subtarget.isTargetWin64()) {
     // Conditional tail calls confuse the Win64 unwinder.
+    // TODO: Allow them for "leaf" functions; PR30337.
     return false;
   }
 
@@ -4289,7 +4289,8 @@ bool X86InstrInfo::canMakeTailCallConditional(
     return false;
   }
 
-  const X86MachineFunctionInfo *X86FI = MF->getInfo<X86MachineFunctionInfo>();
+  const X86MachineFunctionInfo *X86FI =
+      TailCall.getParent()->getParent()->getInfo<X86MachineFunctionInfo>();
   if (X86FI->getTCReturnAddrDelta() != 0 ||
       TailCall.getOperand(1).getImm() != 0) {
     // A conditional tail call cannot do any stack adjustment.
diff --git a/llvm/test/CodeGen/X86/conditional-tailcall.ll b/llvm/test/CodeGen/X86/conditional-tailcall.ll
index 331697c..502643d 100644
--- a/llvm/test/CodeGen/X86/conditional-tailcall.ll
+++ b/llvm/test/CodeGen/X86/conditional-tailcall.ll
@@ -1,6 +1,5 @@
-; RUN: llc < %s -mtriple=i686-linux -show-mc-encoding | FileCheck -check-prefix=CHECK %s
-; RUN: llc < %s -mtriple=x86_64-linux -show-mc-encoding | FileCheck -check-prefix=CHECK %s
-; RUN: llc < %s -mtriple=x86_64-win32 -show-mc-encoding | FileCheck -check-prefix=CHECK -check-prefix=WIN64 %s
+; RUN: llc < %s -mtriple=i686-linux -show-mc-encoding | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-linux -show-mc-encoding | FileCheck %s
 
 declare void @foo()
 declare void @bar()
@@ -24,28 +23,6 @@ bb2:
 ; CHECK: jmp foo
 }
 
-define void @f_non_leaf(i32 %x, i32 %y) optsize {
-entry:
-  ; Force %ebx to be spilled on the stack, turning this into
-  ; not a "leaf" function for Win64.
-  tail call void asm sideeffect "", "~{ebx}"()
-
-	%p = icmp eq i32 %x, %y
-  br i1 %p, label %bb1, label %bb2
-bb1:
-  tail call void @foo()
-  ret void
-bb2:
-  tail call void @bar()
-  ret void
-
-; CHECK-LABEL: f_non_leaf:
-; WIN64-NOT: je foo
-; WIN64-NOT: jne bar
-; WIN64: jne
-; WIN64: jmp foo
-; WIN64: jmp bar
-}
 
 declare x86_thiscallcc zeroext i1 @baz(i8*, i32)
 define x86_thiscallcc zeroext i1 @BlockPlacementTest(i8* %this, i32 %x) optsize {
-- 
2.7.4