[PATCH] Improve performance of vector code on A15

[Tim Northover]

Hi Silviu,

I've taken a quick look at the patch. It's a relief not to have to
think about implicit-defs! I mostly just spotted cosmetic things.

+    std::vector<unsigned> getReadDPRs(MachineInstr *MI);

Have you considered a SmallVector here (and elideCopiesAndPHIs)? It
could well be better here, just want to make sure you've thought about
it.

+// Returns true if this is a use of a SPR register.

Doxygen-style comments on functions would be good.

+bool A15SDOptimizer::usesSReg(MachineOperand &MO) {
+bool A15SDOptimizer::usesDReg(MachineOperand &MO) {
+bool A15SDOptimizer::usesQReg(MachineOperand &MO) {

These all duplicate each other. It might be worth making them delegate
to a function taking a TargetRegisterClass

+unsigned A15SDOptimizer::widenConstantPoolLoad(MachineInstr *MI) {

It's not always valid to do this with a VLDR.F64. If the constant
happened to be just before a page-boundary into unallocated memory
then it could fault. Fortunately, there appears to be a duplicating
VLD1 instruction that you could use instead.

+        //regclass as DPRMI? (i.e. a DPR or QPR).

Space.

+  //   * INSERT_SUBREG: * If the SPR value was originally in another DPR/QPR
+  //                    lane, and the other lane(s) of the DPR/QPR register
+  //                    that we are inserting in are undefined, use the
+  //                    original DPR/QPR value.

In monospace, the sublist is a little tricky to read. Might be worth
putting a couple more spaces on subsequent lines.

I still think it's worth doing a bit more thorough checking of the
code sequences used in the tests: whether the registers are marshalled
in a correct way for example.

Cheers.

Tim.