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

llvm-svn: 169796

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 21bb1476440..c3a5e6472ef 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -2284,6 +2284,9 @@ bool ARMFastISel::SelectCall(const Instruction *I,
   // Can't handle inline asm.
   if (isa<InlineAsm>(Callee)) return false;
 
+  // Allow SelectionDAG isel to handle tail calls.
+  if (CI->isTailCall()) return false;
+
   // Check the calling convention.
   ImmutableCallSite CS(CI);
   CallingConv::ID CC = CS.getCallingConv();