Improve and unify the handling of addressing modes in RyuJIT

[CarolEidt]

There are several issues with the handling of addressing modes:

• The method that does the analysis to determine whether an addressing mode should be used, genCreateAddrMode(), is invoked multiple times. In RyuJIT (i.e. non-legacy code) this is in gtSetEvalOrder() and in Lowering::SetIndirAddrOpCounts(). This is not only wasteful, but it is not clear that they are consistent in which nodes are being considered. This means that some nodes might be marked GTF_ADDRMODE_NO_CSE but not actually become addresing modes, and vice-versa.
• The source and destination address for block operations (copyBlk and InitBlk) are not considered as candidates for addressing modes in gtSetEvalOrder(), but are in LowerAdd(), as long as they have not been transformed into regular indirections.
• Similarly, GT_OBJ nodes are not considered for addressing modes, although they are also indirections.
• The code is not currently well structured to be target-independent.

We should do the analysis once in the front-end and instantiate the addressing modes at that time, and should strongly consider factoring the analysis out from the code generation, which is currently enabled or disabled by an argument to genCreateAddrMode().

category:cq theme:big-bets skill-level:expert cost:large

[TIHan]

• After looking at gtSetEvalOrder(), we do still call into genCreateAddrMode from gtMarkAddrMode. It's also called by gtGetIndNodeCost and gtSetMultiOpOrder which are called by gtSetEvalOrder().
• Lowering::SetIndirAddrOpCounts looks to be removed or renamed.
• GT_OBJ is gone now.
• Below is LowerAdd:

#ifdef TARGET_XARCH
        if (BlockRange().TryGetUse(node, &use))
        {
            // If this is a child of an ordinary indir, let the parent handle it.
            // If there is a chain of adds, only look at the topmost one.
            GenTree* parent = use.User();
            if ((!parent->OperIsIndir() || parent->OperIsAtomicOp()) && !parent->OperIs(GT_ADD))
            {
                TryCreateAddrMode(node, false, parent);
            }
        }
#endif // TARGET_XARCH

TryCreateAddrMode will do the analysis to see if it can create an address mode:

    // Find out if an addressing mode can be constructed
    bool doAddrMode = comp->codeGen->genCreateAddrMode(addr,     // address
                                                       true,     // fold
                                                       &rev,     // reverse ops
                                                       &base,    // base addr
                                                       &index,   // index val
                                                       &scale,   // scaling
                                                       &offset); // displacement

Improvements can still be made here it looks like, though a bit uncertain of how much effort would be needed and the benefit.