[llvm-commits] [llvm] r66976 - in /llvm/trunk: lib/CodeGen/PHIElimination.cpp lib/Transforms/Scalar/CodeGenPrepare.cpp test/CodeGen/X86/2009-03-13-PHIElimBug.ll test/CodeGen/X86/split-eh-lpad-edges.ll

[Duncan Sands]

Hi Evan, thanks for fixing this.

> +void PNE::WalkPassEHTryRange(MachineBasicBlock &MBB,
> +                             MachineBasicBlock::iterator &I, unsigned SrcReg) {
> +  if (I == MBB.begin())
> +    return;
> +  MachineBasicBlock::iterator PI = prior(I);
> +  if (PI->getOpcode() != TargetInstrInfo::EH_LABEL)
> +    return;

If the invoke returns a result, then the block will not end with an EH_LABEL,
it will end with a register copy.  For example:

        %reg1031<def> = MOV32rr %EAX
        EH_LABEL 2
        %reg1025<def> = MOV32rr %reg1031  <= Invoke result, not an EH_LABEL
        JMP mbb<entry.cont_crit_edge,0xa11af90>

So in this case the logic bails out, putting the copy at the end of the BB,
even though it might still need to be before the invoke.

> +  // Trying to walk pass the EH try range. If we run into a use instruction,
> +  // we want to insert the copy there.

Why is that?  I don't understand why uses matter.  Can't you just always put the
copy immediately after the definition of SrcReg?  If so, you wouldn't need to
scan for EH_LABEL's etc.

Ciao,

Duncan.