[AArch64][GlobalISel] Tail call memory intrinsics
Because memory intrinsics are handled differently than other calls, we need to
check them for tail call eligiblity in the legalizer. This allows us to still
inline them when it's beneficial to do so, but also tail call when possible.
This adds simple tail calling support for when the intrinsic is followed by a
return.
It ports the attribute checks from `TargetLowering::isInTailCallPosition` into
a similarly-named function in LegalizerHelper.cpp. The target-specific
`isUsedByReturnOnly` hook is not ported here.
Update tailcall-mem-intrinsics.ll to show that GlobalISel can now tail call
memory intrinsics.
Update legalize-memcpy-et-al.mir to have a case where we don't tail call.
Differential Revision: https://reviews.llvm.org/D67566
llvm-svn: 371893
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index fbb817e..9239576 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -327,6 +327,35 @@
llvm_unreachable("Unknown libcall function");
}
+/// True if an instruction is in tail position in its caller. Intended for
+/// legalizing libcalls as tail calls when possible.
+static bool isLibCallInTailPosition(MachineInstr &MI) {
+ const Function &F = MI.getParent()->getParent()->getFunction();
+
+ // Conservatively require the attributes of the call to match those of
+ // the return. Ignore NoAlias and NonNull because they don't affect the
+ // call sequence.
+ AttributeList CallerAttrs = F.getAttributes();
+ if (AttrBuilder(CallerAttrs, AttributeList::ReturnIndex)
+ .removeAttribute(Attribute::NoAlias)
+ .removeAttribute(Attribute::NonNull)
+ .hasAttributes())
+ return false;
+
+ // It's not safe to eliminate the sign / zero extension of the return value.
+ if (CallerAttrs.hasAttribute(AttributeList::ReturnIndex, Attribute::ZExt) ||
+ CallerAttrs.hasAttribute(AttributeList::ReturnIndex, Attribute::SExt))
+ return false;
+
+ // Only tail call if the following instruction is a standard return.
+ auto &TII = *MI.getMF()->getSubtarget().getInstrInfo();
+ MachineInstr *Next = MI.getNextNode();
+ if (!Next || TII.isTailCall(*Next) || !Next->isReturn())
+ return false;
+
+ return true;
+}
+
LegalizerHelper::LegalizeResult
llvm::createLibcall(MachineIRBuilder &MIRBuilder, RTLIB::Libcall Libcall,
const CallLowering::ArgInfo &Result,
@@ -407,10 +436,24 @@
Info.CallConv = TLI.getLibcallCallingConv(RTLibcall);
Info.Callee = MachineOperand::CreateES(Name);
Info.OrigRet = CallLowering::ArgInfo({0}, Type::getVoidTy(Ctx));
+ Info.IsTailCall = isLibCallInTailPosition(MI);
+
std::copy(Args.begin(), Args.end(), std::back_inserter(Info.OrigArgs));
if (!CLI.lowerCall(MIRBuilder, Info))
return LegalizerHelper::UnableToLegalize;
+ if (Info.LoweredTailCall) {
+ assert(Info.IsTailCall && "Lowered tail call when it wasn't a tail call?");
+ // We must have a return following the call to get past
+ // isLibCallInTailPosition.
+ assert(MI.getNextNode() && MI.getNextNode()->isReturn() &&
+ "Expected instr following MI to be a return?");
+
+ // We lowered a tail call, so the call is now the return from the block.
+ // Delete the old return.
+ MI.getNextNode()->eraseFromParent();
+ }
+
return LegalizerHelper::Legalized;
}
