RegsToPass.push_back(std::make_pair(unsigned(X86::EBX),
DAG.getNode(X86ISD::GlobalBaseReg, SDLoc(), getPointerTy())));
} else {
- // If we are tail calling a global or external symbol in GOT pic mode, we
- // cannot use a direct jump, since that would make lazy dynamic linking
- // impossible (see PR15086). So pretend this is not a tail call, to
- // prevent the optimization to a jump.
+ // If we are tail calling and generating PIC/GOT style code load the
+ // address of the callee into ECX. The value in ecx is used as target of
+ // the tail jump. This is done to circumvent the ebx/callee-saved problem
+ // for tail calls on PIC/GOT architectures. Normally we would just put the
+ // address of GOT into ebx and then call target@PLT. But for tail calls
+ // ebx would be restored (since ebx is callee saved) before jumping to the
+ // target@PLT.
+
+ // Note: The actual moving to ECX is done further down.
GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
- if ((G && !G->getGlobal()->hasHiddenVisibility() &&
- !G->getGlobal()->hasProtectedVisibility()) ||
- isa<ExternalSymbolSDNode>(Callee))
- isTailCall = false;
+ if (G && !G->getGlobal()->hasHiddenVisibility() &&
+ !G->getGlobal()->hasProtectedVisibility())
+ Callee = LowerGlobalAddress(Callee, DAG);
+ else if (isa<ExternalSymbolSDNode>(Callee))
+ Callee = LowerExternalSymbol(Callee, DAG);
}
}
entry:
%tmp11 = tail call fastcc i32 @tailcallee( i32 %in1, i32 %in2, i32 %in1, i32 %in2 ) ; <i32> [#uses=1]
ret i32 %tmp11
-; Note that this call via PLT could be further optimized into a direct call (no GOT, no PLT):
-; CHECK: calll tailcallee@PLT
+; CHECK: movl tailcallee@GOT
+; CHECK: jmpl
}