[PredicateInfo] Don't use depth first walk (NFCI)

The order in which we collect the predicates does not matter, as
they will be sorted anyway. As such, avoid the expensive depth
first walk over the dominator tree and instead use plain iteration
over the function.

Author: nikic

llvm/lib/Transforms/Utils/PredicateInfo.cpp

@@ -488,17 +488,19 @@ void PredicateInfoBuilder::buildPredicateInfo() {
   // Collect operands to rename from all conditional branch terminators, as well
   // as assume statements.
   SmallVector<Value *, 8> OpsToRename;
-  for (auto *DTN : depth_first(DT.getRootNode())) {
-    BasicBlock *BranchBB = DTN->getBlock();
-    if (auto *BI = dyn_cast<BranchInst>(BranchBB->getTerminator())) {
+  for (BasicBlock &BB : F) {
+    if (!DT.isReachableFromEntry(&BB))
+      continue;
+
+    if (auto *BI = dyn_cast<BranchInst>(BB.getTerminator())) {
       if (!BI->isConditional())
         continue;
       // Can't insert conditional information if they all go to the same place.
       if (BI->getSuccessor(0) == BI->getSuccessor(1))
         continue;
-      processBranch(BI, BranchBB, OpsToRename);
-    } else if (auto *SI = dyn_cast<SwitchInst>(BranchBB->getTerminator())) {
-      processSwitch(SI, BranchBB, OpsToRename);
+      processBranch(BI, &BB, OpsToRename);
+    } else if (auto *SI = dyn_cast<SwitchInst>(BB.getTerminator())) {
+      processSwitch(SI, &BB, OpsToRename);
     }
   }
   for (auto &Assume : AC.assumptions()) {