Fall back to the selection dag isel to select tail calls.

This shouldn't affect codegen for -O0 compiles as tail call markers are not
emitted in unoptimized compiles.  Testing with the external/internal nightly
test suite reveals no change in compile time performance.  Testing with -O1,
-O2 and -O3 with fast-isel enabled did not cause any compile-time or
execution-time failures.  All tests were performed on my x86 machine.
I'll monitor our arm testers to ensure no regressions occur there.

In an upcoming clang patch I will be marking the objc_autoreleaseReturnValue
and objc_retainAutoreleaseReturnValue as tail calls unconditionally.  While
it's theoretically true that this is just an optimization, it's an
optimization that we very much want to happen even at -O0, or else ARC
applications become substantially harder to debug.

Part of rdar://12553082

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169796 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 0 insertions, 5 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 97d975ecb7..ee8f272093 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5273,11 +5273,6 @@ void SelectionDAGBuilder::LowerCallTo(ImmutableCallSite CS, SDValue Callee,
       !isInTailCallPosition(CS, CS.getAttributes().getRetAttributes(), TLI))
     isTailCall = false;
 
-  // If there's a possibility that fast-isel has already selected some amount
-  // of the current basic block, don't emit a tail call.
-  if (isTailCall && TM.Options.EnableFastISel)
-    isTailCall = false;
-
   TargetLowering::
   CallLoweringInfo CLI(getRoot(), RetTy, FTy, isTailCall, Callee, Args, DAG,
                        getCurDebugLoc(), CS);