[ADCE] Remove redundent code [NFC]

[grosser]

Summary

In commit r289548 ([ADCE] Add code to remove dead branches) a redundant loop
nest was accidentally introduced, which implements exactly the same
functionality as has already been available right after. This redundancy has
been found when inspecting the ADCE code in the context of our recent
discussions on post-dominator modeling. This redundant code was also eliminated
by r296535 (which sparked the discussion), but only as part of a larger semantic
change of the post-dominance modeling. As this redundency in [ADCE] is really
just an oversight completely independent of the post-dominance changes under
discussion, we remove this redundancy independently.

[grosser]

Hi Daniel,

I pulled this one out, as I believe this will make it easier to understand the impact of the actual post-dom tree.

Btw., thanks for your now very concrete requirement statement. I will reply to the thread soonish.

[• dberlin]

LGTM.

llvm/trunk/lib/Transforms/Scalar/ADCE.cpp

void AggressiveDeadCodeElimination::initialize() {
   // return of the function or a successor for which this is true.
   // This protects IDFCalculator which cannot handle such blocks.
   for (auto &BBInfoPair : BlockInfo) {
     auto &BBInfo = BBInfoPair.second;
     if (BBInfo.terminatorIsLive())
       continue;
     auto *BB = BBInfo.BB;
     if (!PDT.getNode(BB)) {
-      markLive(BBInfo.Terminator);
-      continue;
-    }
-    for (auto *Succ : successors(BB))
-      if (!PDT.getNode(Succ)) {
-        markLive(BBInfo.Terminator);
-        break;
-      }
-  }
-
-  // Mark blocks live if there is no path from the block to the
-  // return of the function or a successor for which this is true.
-  // This protects IDFCalculator which cannot handle such blocks.
-  for (auto &BBInfoPair : BlockInfo) {
-    auto &BBInfo = BBInfoPair.second;
-    if (BBInfo.terminatorIsLive())
-      continue;
-    auto *BB = BBInfo.BB;
-    if (!PDT.getNode(BB)) {
       DEBUG(dbgs() << "Not post-dominated by return: " << BB->getName()
                    << '\n';);
       markLive(BBInfo.Terminator);
       continue;
     }
     for (auto *Succ : successors(BB))
       if (!PDT.getNode(Succ)) {
         DEBUG(dbgs() << "Successor not post-dominated by return: "