Fix PR672 another way which should be more robust
llvm-svn: 24585
diff --git a/llvm/lib/Target/X86/X86ISelPattern.cpp b/llvm/lib/Target/X86/X86ISelPattern.cpp
index 28f799e..6132c94 100644
--- a/llvm/lib/Target/X86/X86ISelPattern.cpp
+++ b/llvm/lib/Target/X86/X86ISelPattern.cpp
@@ -3014,7 +3014,10 @@
bool isDirect = isa<GlobalAddressSDNode>(Callee) ||
isa<ExternalSymbolSDNode>(Callee);
unsigned CalleeReg = 0;
- if (!isDirect) CalleeReg = SelectExpr(Callee);
+ if (!isDirect) {
+ // If this is not a direct tail call, evaluate the callee's address.
+ CalleeReg = SelectExpr(Callee);
+ }
unsigned RegOp1 = 0;
unsigned RegOp2 = 0;
@@ -3059,6 +3062,15 @@
break;
}
}
+
+ // If this is not a direct tail call, put the callee's address into ECX.
+ // The address has to be evaluated into a non-callee save register that is
+ // not used for arguments. This means either ECX, as EAX and EDX may be
+ // used for argument passing. We do this here to make sure that the
+ // expressions for arguments and callee are all evaluated before the copies
+ // into physical registers.
+ if (!isDirect)
+ BuildMI(BB, X86::MOV32rr, 1, X86::ECX).addReg(CalleeReg);
// Adjust ESP.
if (ESPOffset)
@@ -3067,21 +3079,7 @@
// TODO: handle jmp [mem]
if (!isDirect) {
- // We do not want the register allocator to allocate CalleeReg to a callee
- // saved register, as these will be restored before the JMP. To prevent
- // this, emit explicit clobbers of callee saved regs here. A better way to
- // solve this would be to specify that the register constraints of TAILJMPr
- // only allow registers that are not callee saved, but we currently can't
- // express that. This forces all four of these regs to be saved and
- // reloaded for all functions with an indirect tail call.
- // TODO: Improve this!
- BuildMI(BB, X86::IMPLICIT_DEF, 4)
- .addReg(X86::ESI, MachineOperand::Def)
- .addReg(X86::EDI, MachineOperand::Def)
- .addReg(X86::EBX, MachineOperand::Def)
- .addReg(X86::EBP, MachineOperand::Def);
-
- BuildMI(BB, X86::TAILJMPr, 1).addReg(CalleeReg);
+ BuildMI(BB, X86::TAILJMPr, 1).addReg(X86::ECX);
} else if (GlobalAddressSDNode *GASD = dyn_cast<GlobalAddressSDNode>(Callee)){
BuildMI(BB, X86::TAILJMPd, 1).addGlobalAddress(GASD->getGlobal(), true);
} else {