From: Dan Gohman <gohman@apple.com>
Date: Mon, 8 Feb 2010 20:34:14 +0000 (+0000)
Subject: In guaranteed tailcall mode, don't decline the tailcall optimization
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=c2e93b255e120f066ad8c16b0593b05f7e9f3d19;p=oota-llvm.git

In guaranteed tailcall mode, don't decline the tailcall optimization
for blocks ending in "unreachable".


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95565 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index cf342c793b9..93ae043dbc1 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4205,13 +4205,16 @@ 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.
-  // 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;
+  // The block must end in a return statement or unreachable.
+  //
+  // FIXME: Decline tailcall if it's not guaranteed and 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 &&
+      (!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
 
   // If I will have a chain, make sure no other instruction that will have a
   // chain interposes between I and the return.
diff --git a/test/CodeGen/X86/tailcall1.ll b/test/CodeGen/X86/tailcall1.ll
index d08919e668c..f7ff5d5308d 100644
--- a/test/CodeGen/X86/tailcall1.ll
+++ b/test/CodeGen/X86/tailcall1.ll
@@ -1,4 +1,7 @@
-; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL | count 4
+; RUN: llc < %s -march=x86 -tailcallopt | grep TAILCALL | count 5
+
+; With -tailcallopt, CodeGen guarantees a tail call optimization
+; for all of these.
 
 declare fastcc i32 @tailcallee(i32 %a1, i32 %a2, i32 %a3, i32 %a4)