From febc81680c80a53f15f85b1812cba07fc179b9fd Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 3 Feb 2010 03:55:59 +0000
Subject: [PATCH] Revert 94937 and move the noreturn check to codegen.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95198 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp   |  9 +++++++--
 lib/Transforms/Scalar/TailRecursionElimination.cpp |  9 ++++-----
 test/CodeGen/X86/tailcall1.ll                      |  2 +-
 test/CodeGen/X86/tailcall2.ll                      | 13 +++++++++++++
 test/Transforms/TailCallElim/no-return-calls.ll    | 12 ------------
 5 files changed, 25 insertions(+), 20 deletions(-)
 delete mode 100644 test/Transforms/TailCallElim/no-return-calls.ll

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 495418d999e..3a25714f07c 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4205,8 +4205,13 @@ isInTailCallPosition(CallSite CS, Attributes CalleeRetAttr,
   const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
   const Function *F = ExitBB->getParent();
 
-  // The block must end in a return statement or an unreachable.
-  if (!Ret && !isa<UnreachableInst>(Term)) return false;
+  // The block must end in a return statement.
+  // FIXME: Disallow tailcall if the block ends in an unreachable for now.
+  // The way tailcall optimization is currently implemented means it will
+  // add an epilogue followed by a jump. That is not profitable. Also, if
+  // the callee is a special function (e.g. longjmp on x86), it can end up
+  // causing miscompilation that has not been fully understood.
+  if (!Ret) return false;
 
   // Unless we are explicitly forcing tailcall optimization do not tailcall if
   // the called function is bitcast'ed. The analysis may not be entirely
diff --git a/lib/Transforms/Scalar/TailRecursionElimination.cpp b/lib/Transforms/Scalar/TailRecursionElimination.cpp
index 913dd73cc17..162d902cfa4 100644
--- a/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -184,11 +184,10 @@ bool TailCallElim::runOnFunction(Function &F) {
   if (!FunctionContainsEscapingAllocas)
     for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
       for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
-        if (CallInst *CI = dyn_cast<CallInst>(I))
-          if (!CI->doesNotReturn()) {
-            CI->setTailCall();
-            MadeChange = true;
-          }
+        if (CallInst *CI = dyn_cast<CallInst>(I)) {
+          CI->setTailCall();
+          MadeChange = true;
+        }
 
   return MadeChange;
 }
diff --git a/test/CodeGen/X86/tailcall1.ll b/test/CodeGen/X86/tailcall1.ll
index 96c4cad9799..d08919e668c 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 | count 5
+; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL | count 4
 
 declare fastcc i32 @tailcallee(i32 %a1, i32 %a2, i32 %a3, i32 %a4)
 
diff --git a/test/CodeGen/X86/tailcall2.ll b/test/CodeGen/X86/tailcall2.ll
index 81419dc387e..3cd8b26f608 100644
--- a/test/CodeGen/X86/tailcall2.ll
+++ b/test/CodeGen/X86/tailcall2.ll
@@ -127,3 +127,16 @@ entry:
   %1 = tail call signext i16 %0(i32 0) nounwind
   ret i16 %1
 }
+
+define void @t10() nounwind ssp {
+entry:
+; 32: t10:
+; 32: call
+
+; 64: t10:
+; 64: callq
+  %0 = tail call i32 @foo4() noreturn nounwind
+  unreachable
+}
+
+declare i32 @foo4()
diff --git a/test/Transforms/TailCallElim/no-return-calls.ll b/test/Transforms/TailCallElim/no-return-calls.ll
deleted file mode 100644
index f5643ae3330..00000000000
--- a/test/Transforms/TailCallElim/no-return-calls.ll
+++ /dev/null
@@ -1,12 +0,0 @@
-; RUN: opt < %s -tailcallelim -S | FileCheck %s
-
-define void @t() nounwind ssp {
-entry:
-; CHECK: entry:
-; CHECK: %0 = call i32 @foo()
-; CHECK: ret void
-  %0 = call i32 @foo() nounwind noreturn
-  ret void
-}
-
-declare i32 @foo()
-- 
2.34.1