From 22de16dc7582dac43429ce0dcb374604020c01f5 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Thu, 19 Jan 2012 00:34:10 +0000
Subject: Add a TargetOption for disabling tail calls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148442 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Target/TargetOptions.h  |  9 ++++++--
 lib/Target/X86/X86ISelLowering.cpp   |  5 ++++-
 test/CodeGen/X86/tailcall-disable.ll | 40 ++++++++++++++++++++++++++++++++++++
 tools/llc/llc.cpp                    |  6 ++++++
 4 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 test/CodeGen/X86/tailcall-disable.ll

diff --git a/include/llvm/Target/TargetOptions.h b/include/llvm/Target/TargetOptions.h
index 3f42bbe16a..852e67f582 100644
--- a/include/llvm/Target/TargetOptions.h
+++ b/include/llvm/Target/TargetOptions.h
@@ -43,8 +43,9 @@ namespace llvm {
           NoNaNsFPMath(false), HonorSignDependentRoundingFPMathOption(false),
           UseSoftFloat(false), NoZerosInBSS(false), JITExceptionHandling(false),
           JITEmitDebugInfo(false), JITEmitDebugInfoToDisk(false),
-          GuaranteedTailCallOpt(false), StackAlignmentOverride(0),
-          RealignStack(true), DisableJumpTables(false), EnableFastISel(false),
+          GuaranteedTailCallOpt(false), DisableTailCalls(false),
+          StackAlignmentOverride(0), RealignStack(true),
+          DisableJumpTables(false), EnableFastISel(false),
           EnableSegmentedStacks(false), TrapFuncName(""),
           FloatABIType(FloatABI::Default)
     {}
@@ -147,6 +148,10 @@ namespace llvm {
     /// as their parent function, etc.), using an alternate ABI if necessary.
     unsigned GuaranteedTailCallOpt : 1;
 
+    /// DisableTailCalls - This flag controls whether we will use tail calls.
+    /// Disabling them may be useful to maintain a correct call stack.
+    unsigned DisableTailCalls : 1;
+
     /// StackAlignmentOverride - Override default stack alignment for target.
     unsigned StackAlignmentOverride;
 
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 91dc7b51d8..858ebc5de5 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -1732,7 +1732,7 @@ static bool IsTailCallConvention(CallingConv::ID CC) {
 }
 
 bool X86TargetLowering::mayBeEmittedAsTailCall(CallInst *CI) const {
-  if (!CI->isTailCall())
+  if (!CI->isTailCall() || getTargetMachine().Options.DisableTailCalls)
     return false;
 
   CallSite CS(CI);
@@ -2133,6 +2133,9 @@ X86TargetLowering::LowerCall(SDValue Chain, SDValue Callee,
   bool IsStructRet    = CallIsStructReturn(Outs);
   bool IsSibcall      = false;
 
+  if (MF.getTarget().Options.DisableTailCalls)
+    isTailCall = false;
+
   if (isTailCall) {
     // Check if it's really possible to do a tail call.
     isTailCall = IsEligibleForTailCallOptimization(Callee, CallConv,
diff --git a/test/CodeGen/X86/tailcall-disable.ll b/test/CodeGen/X86/tailcall-disable.ll
new file mode 100644
index 0000000000..a561b74609
--- /dev/null
+++ b/test/CodeGen/X86/tailcall-disable.ll
@@ -0,0 +1,40 @@
+; RUN: llc -disable-tail-calls < %s | FileCheck --check-prefix=CALL %s
+; RUN: llc < %s | FileCheck --check-prefix=JMP %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @helper() nounwind {
+entry:
+  ret i32 7
+}
+
+define i32 @test1() nounwind {
+entry:
+  %call = tail call i32 @helper()
+  ret i32 %call
+}
+
+;CALL: test1:
+;CALL-NOT: ret
+;CALL: callq helper
+;CALL: ret
+
+;JMP: test1:
+;JMP-NOT: ret
+;JMP: jmp helper # TAILCALL
+
+define i32 @test2() nounwind {
+entry:
+  %call = tail call i32 @test2()
+  ret i32 %call
+}
+
+;CALL: test2:
+;CALL-NOT: ret
+;CALL: callq test2
+;CALL: ret
+
+;JMP: test2:
+;JMP-NOT: ret
+;JMP: jmp test2 # TAILCALL
diff --git a/tools/llc/llc.cpp b/tools/llc/llc.cpp
index 790f9e6027..5fabdaf069 100644
--- a/tools/llc/llc.cpp
+++ b/tools/llc/llc.cpp
@@ -237,6 +237,11 @@ EnableGuaranteedTailCallOpt("tailcallopt",
   cl::desc("Turn fastcc calls into tail calls by (potentially) changing ABI."),
   cl::init(false));
 
+static cl::opt<bool>
+DisableTailCalls("disable-tail-calls",
+  cl::desc("Never emit tail calls"),
+  cl::init(false));
+
 static cl::opt<unsigned>
 OverrideStackAlignment("stack-alignment",
   cl::desc("Override default stack alignment"),
@@ -462,6 +467,7 @@ int main(int argc, char **argv) {
   Options.JITEmitDebugInfo = EmitJitDebugInfo;
   Options.JITEmitDebugInfoToDisk = EmitJitDebugInfoToDisk;
   Options.GuaranteedTailCallOpt = EnableGuaranteedTailCallOpt;
+  Options.DisableTailCalls = DisableTailCalls;
   Options.StackAlignmentOverride = OverrideStackAlignment;
   Options.RealignStack = EnableRealignStack;
   Options.DisableJumpTables = DisableSwitchTables;
-- 
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