unsigned Reg = I->getReg();
Offset = MaxOffset - Offset + saveAreaOffset;
+ // Don't output a new machine move if we're re-saving the frame
+ // pointer. This happens when the PrologEpilogInserter has inserted an extra
+ // "PUSH" of the frame pointer -- the "emitPrologue" method automatically
+ // generates one when frame pointers are used. If we generate a "machine
+ // move" for this extra "PUSH", the linker will lose track of the fact that
+ // the frame pointer should have the value of the first "PUSH" when it's
+ // trying to unwind.
+ //
+ // FIXME: This looks inelegant. It's possibly correct, but it's covering up
+ // another bug. I.e., one where we generate a prolog like this:
+ //
+ // pushl %ebp
+ // movl %esp, %ebp
+ // pushl %ebp
+ // pushl %esi
+ // ...
+ //
+ // The immediate re-push of EBP is unnecessary. At the least, it's an
+ // optimization bug. EBP can be used as a scratch register in certain
+ // cases, but probably not when we have a frame pointer.
+ if (HasFP && FramePtr == Reg)
+ continue;
+
MachineLocation CSDst(MachineLocation::VirtualFP, Offset);
MachineLocation CSSrc(Reg);
Moves.push_back(MachineMove(LabelId, CSDst, CSSrc));