From 01205a80f5c789234029813f8c09488891c0b23e Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Fri, 13 Nov 2009 18:49:38 +0000
Subject: [PATCH] Don't let a noalias difference disrupt the tailcall
 optimization.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88672 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp |  7 ++++---
 test/CodeGen/X86/tailcall1.ll                  | 16 +++++++++++++++-
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
index b3d8d1dbee6..f2c623cd616 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
@@ -4349,7 +4349,7 @@ SelectionDAGLowering::visitIntrinsicCall(CallInst &I, unsigned Intrinsic) {
 /// TargetLowering::IsEligibleForTailCallOptimization.
 ///
 static bool
-isInTailCallPosition(const Instruction *I, Attributes RetAttr,
+isInTailCallPosition(const Instruction *I, Attributes CalleeRetAttr,
                      const TargetLowering &TLI) {
   const BasicBlock *ExitBB = I->getParent();
   const TerminatorInst *Term = ExitBB->getTerminator();
@@ -4377,8 +4377,9 @@ isInTailCallPosition(const Instruction *I, Attributes RetAttr,
   if (!Ret || Ret->getNumOperands() == 0) return true;
 
   // Conservatively require the attributes of the call to match those of
-  // the return.
-  if (F->getAttributes().getRetAttributes() != RetAttr)
+  // the return. Ignore noalias because it doesn't affect the call sequence.
+  unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
+  if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
     return false;
 
   // Otherwise, make sure the unmodified return value of I is the return value.
diff --git a/test/CodeGen/X86/tailcall1.ll b/test/CodeGen/X86/tailcall1.ll
index a4f87c021a9..215d00946dd 100644
--- a/test/CodeGen/X86/tailcall1.ll
+++ b/test/CodeGen/X86/tailcall1.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL
+; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL | count 3
 define fastcc i32 @tailcallee(i32 %a1, i32 %a2, i32 %a3, i32 %a4) {
 entry:
 	ret i32 %a3
@@ -9,3 +9,17 @@ entry:
 	%tmp11 = tail call fastcc i32 @tailcallee( i32 %in1, i32 %in2, i32 %in1, i32 %in2 )		; <i32> [#uses=1]
 	ret i32 %tmp11
 }
+
+declare fastcc i8* @alias_callee()
+
+define fastcc noalias i8* @noalias_caller() nounwind {
+  %p = tail call fastcc i8* @alias_callee()
+  ret i8* %p
+}
+
+declare fastcc noalias i8* @noalias_callee()
+
+define fastcc i8* @alias_caller() nounwind {
+  %p = tail call fastcc noalias i8* @noalias_callee()
+  ret i8* %p
+}
-- 
2.11.0