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Perform sibcall in some cases when arguments are passes memory. Look for cases

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where callee's arguments are already in the caller's own caller's stack and
they line up perfectly. e.g.

extern int foo(int a, int b, int c);

int bar(int a, int b, int c) {
  return foo(a, b, c);
}


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95053 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-02-02 02:22:50 +00:00
parent d74667e226
commit b2c9290a01
2 changed files with 62 additions and 6 deletions
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55
lib/Target/X86/X86ISelLowering.cpp
View File

@ -1807,6 +1807,10 @@ X86TargetLowering::LowerCall(SDValue Chain, SDValue Callee,
unsigned NumBytes = CCInfo.getNextStackOffset();
if (FuncIsMadeTailCallSafe(CallConv))
NumBytes = GetAlignedArgumentStackSize(NumBytes, DAG);
else if (isTailCall && !PerformTailCallOpt)
// This is a sibcall. The memory operands are available in caller's
// own caller's stack.
NumBytes = 0;
int FPDiff = 0;
if (isTailCall) {
@ -1976,9 +1980,11 @@ X86TargetLowering::LowerCall(SDValue Chain, SDValue Callee,
int FI = 0;
// Do not flag preceeding copytoreg stuff together with the following stuff.
InFlag = SDValue();
for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
CCValAssign &VA = ArgLocs[i];
if (!VA.isRegLoc()) {
if (PerformTailCallOpt) {
for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
CCValAssign &VA = ArgLocs[i];
if (VA.isRegLoc())
continue;
assert(VA.isMemLoc());
SDValue Arg = Outs[i].Val;
ISD::ArgFlagsTy Flags = Outs[i].Flags;
@ -2259,11 +2265,14 @@ X86TargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
return false;
}
// Look for obvious safe cases to perform tail call optimization that does not
// requite ABI changes. This is what gcc calls sibcall.
// Do not tail call optimize vararg calls for now.
if (isVarArg)
return false;
// Look for obvious safe cases to perform tail call optimization.
// If the callee takes no arguments then go on to check the results of the
// call.
if (!Outs.empty()) {
@ -2273,8 +2282,42 @@ X86TargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
CCState CCInfo(CalleeCC, isVarArg, getTargetMachine(),
ArgLocs, *DAG.getContext());
CCInfo.AnalyzeCallOperands(Outs, CCAssignFnForNode(CalleeCC));
if (CCInfo.getNextStackOffset())
return false;
if (CCInfo.getNextStackOffset()) {
MachineFunction &MF = DAG.getMachineFunction();
if (MF.getInfo<X86MachineFunctionInfo>()->getBytesToPopOnReturn())
return false;
if (Subtarget->isTargetWin64())
// Win64 ABI has additional complications.
return false;
// Check if the arguments are already laid out in the right way as
// the caller's fixed stack objects.
MachineFrameInfo *MFI = MF.getFrameInfo();
for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
CCValAssign &VA = ArgLocs[i];
EVT RegVT = VA.getLocVT();
SDValue Arg = Outs[i].Val;
ISD::ArgFlagsTy Flags = Outs[i].Flags;
if (Flags.isByVal())
return false; // TODO
if (VA.getLocInfo() == CCValAssign::Indirect)
return false;
if (!VA.isRegLoc()) {
LoadSDNode *Ld = dyn_cast<LoadSDNode>(Arg);
if (!Ld)
return false;
SDValue Ptr = Ld->getBasePtr();
FrameIndexSDNode *FINode = dyn_cast<FrameIndexSDNode>(Ptr);
if (!FINode)
return false;
int FI = FINode->getIndex();
if (!MFI->isFixedObjectIndex(FI))
return false;
if (VA.getLocMemOffset() != MFI->getObjectOffset(FI))
return false;
}
}
}
}
// If the caller does not return a value, then this is obviously safe.

13
test/CodeGen/X86/tailcall2.ll
View File

@ -89,3 +89,16 @@ bb1:
}
declare i32 @bar(i32)
define i32 @t7(i32 %a, i32 %b, i32 %c) nounwind ssp {
entry:
; 32: t7:
; 32: jmp {{_?}}bar2
; 64: t7:
; 64: jmp {{_?}}bar2
%0 = tail call i32 @bar2(i32 %a, i32 %b, i32 %c) nounwind
ret i32 %0
}
declare i32 @bar2(i32, i32, i32)