[LV] Ignore more debug info.

[fhahn]

Summary

We can avoid doing some unnecessary work by skipping debug instructions
in a few loops. It also helps to ensure debug instructions do not
prevent vectorization, although I do not have any concrete test cases
for that.

[rengolin]

Seems trivial. instructionsWithoutDebug is just an iterator filter and there are no early continues in the body of the outer loop, so this actually saves time.

I'm not sure there is any case where a debug info would stop vectorisation, but this is a good change regardless.

LGTM, thanks!

[dcaballe]

LGTM!

lib/Transforms/Vectorize/LoopVectorize.cpp

 LoopVectorizationCostModel::getSmallestAndWidestTypes() {
   unsigned MinWidth = -1U;
   unsigned MaxWidth = 8;
   const DataLayout &DL = TheFunction->getParent()->getDataLayout();
 
   // For each block.
   for (BasicBlock *BB : TheLoop->blocks()) {
     // For each instruction in the loop.
-    for (Instruction &I : *BB) {
+    for (Instruction &I : BB->instructionsWithoutDebug()) {
       Type *T = I.getType();
 
       // Skip ignored values.
       if (ValuesToIgnore.find(&I) != ValuesToIgnore.end())
         continue;
 
       // Only examine Loads, Stores and PHINodes.
       if (!isa<LoadInst>(I) && !isa<StoreInst>(I) && !isa<PHINode>(I))
LoopVectorizationCostModel::calculateRegisterUsage(ArrayRef<unsigned> VFs) {
   // Saves the list of instruction indices that are used in the loop.
   SmallPtrSet<Instruction *, 8> Ends;
   // Saves the list of values that are used in the loop but are
   // defined outside the loop, such as arguments and constants.
   SmallPtrSet<Value *, 8> LoopInvariants;
 
   unsigned Index = 0;
   for (BasicBlock *BB : make_range(DFS.beginRPO(), DFS.endRPO())) {
-    for (Instruction &I : *BB) {
+    for (Instruction &I : BB->instructionsWithoutDebug()) {
       IdxToInstr[Index++] = &I;
 
       // Save the end location of each USE.
       for (Value *U : I.operands()) {
         auto *Instr = dyn_cast<Instruction>(U);
 
         // Ignore non-instruction values such as arguments, constants, etc.
         if (!Instr)