Perform trivial tail call optimization for callees with "C" ABI. These are done
even when -tailcallopt is not specified and it does not require changing ABI.
First case is the most trivial one. Perform tail call optimization when both
the caller and callee do not return values and when the callee does not take
any input arguments.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94664 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 6e64475..eb7f481 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -12,6 +12,7 @@
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "x86-isel"
#include "X86.h"
#include "X86InstrBuilder.h"
#include "X86ISelLowering.h"
@@ -39,6 +40,7 @@
#include "llvm/MC/MCSymbol.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/VectorExtras.h"
#include "llvm/Support/CommandLine.h"
@@ -48,6 +50,8 @@
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
+STATISTIC(NumTailCalls, "Number of tail calls");
+
static cl::opt<bool>
DisableMMX("disable-mmx", cl::Hidden, cl::desc("Disable use of MMX"));
@@ -1788,7 +1792,7 @@
if (isTailCall)
// Check if it's really possible to do a tail call.
isTailCall = IsEligibleForTailCallOptimization(Callee, CallConv, isVarArg,
- Ins, DAG);
+ Outs, Ins, DAG);
assert(!(isVarArg && CallConv == CallingConv::Fast) &&
"Var args not supported with calling convention fastcc");
@@ -1806,6 +1810,8 @@
int FPDiff = 0;
if (isTailCall) {
+ ++NumTailCalls;
+
// Lower arguments at fp - stackoffset + fpdiff.
unsigned NumBytesCallerPushed =
MF.getInfo<X86MachineFunctionInfo>()->getBytesToPopOnReturn();
@@ -2237,11 +2243,29 @@
X86TargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
CallingConv::ID CalleeCC,
bool isVarArg,
- const SmallVectorImpl<ISD::InputArg> &Ins,
+ const SmallVectorImpl<ISD::OutputArg> &Outs,
+ const SmallVectorImpl<ISD::InputArg> &Ins,
SelectionDAG& DAG) const {
- if (CalleeCC == CallingConv::Fast &&
- DAG.getMachineFunction().getFunction()->getCallingConv() == CalleeCC)
+ // If -tailcallopt is specified, make fastcc functions tail-callable.
+ const Function *F = DAG.getMachineFunction().getFunction();
+ if (PerformTailCallOpt &&
+ CalleeCC == CallingConv::Fast && F->getCallingConv() == CalleeCC)
return true;
+
+ if (CalleeCC != CallingConv::Fast &&
+ CalleeCC != CallingConv::C)
+ return false;
+
+ // Look for obvious safe cases to perform tail call optimization.
+ // For now, only consider callees which take no arguments and no return
+ // values.
+ if (!Outs.empty())
+ return false;
+
+ if (Ins.empty())
+ // If the caller does not return a value, then this is obviously safe.
+ return F->getReturnType()->isVoidTy();
+
return false;
}