[PredicateInfo] Don't use depth first walk (NFCI) (#145016)

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.

(To be a bit more precise, the predicates and uses for a specific value
are sorted, so this change has no impact on that. It can change the
order in which values are processed in the first place, but that order
is not semantically relevant.)

Author: nikic

llvm/lib/Transforms/Utils/PredicateInfo.cpp

@@ -453,17 +453,19 @@ 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()) {