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
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index ca25274..c755d72 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1113,19 +1113,21 @@
}
bool HadTailCall = false;
+ MachineBasicBlock::iterator SavedInsertPt = FuncInfo->InsertPt;
SelectBasicBlock(Inst, BI, HadTailCall);
+ // If the call was emitted as a tail call, we're done with the block.
+ // We also need to delete any previously emitted instructions.
+ if (HadTailCall) {
+ FastIS->removeDeadCode(SavedInsertPt, FuncInfo->MBB->end());
+ --BI;
+ break;
+ }
+
// Recompute NumFastIselRemaining as Selection DAG instruction
// selection may have handled the call, input args, etc.
unsigned RemainingNow = std::distance(Begin, BI);
NumFastIselFailures += NumFastIselRemaining - RemainingNow;
-
- // If the call was emitted as a tail call, we're done with the block.
- if (HadTailCall) {
- --BI;
- break;
- }
-
NumFastIselRemaining = RemainingNow;
continue;
}