[llvm] [SimplifyCFG] Use hash map to continue hoisting the common instructions (PR #78615)

[Nikita Popov via llvm-commits]

================
@@ -1635,87 +1675,149 @@ bool SimplifyCFGOpt::hoistCommonCodeFromSuccessors(BasicBlock *BB,
   // many instructions we skip, serving as a compilation time control as well as
   // preventing excessive increase of life ranges.
   unsigned NumSkipped = 0;
-  // If we find an unreachable instruction at the beginning of a basic block, we
-  // can still hoist instructions from the rest of the basic blocks.
-  if (SuccIterPairs.size() > 2) {
-    erase_if(SuccIterPairs,
-             [](const auto &Pair) { return isa<UnreachableInst>(Pair.first); });
-    if (SuccIterPairs.size() < 2)
-      return false;
-  }
 
   bool Changed = false;
+  auto *SuccIterPairBegin = SuccIterPairs.begin();
+  ++SuccIterPairBegin;
+  auto BBItrPair = *SuccIterPairBegin++;
+  auto OtherSuccIterPairRange =
+      iterator_range(SuccIterPairBegin, SuccIterPairs.end());
+
+  DenseMap<llvm::hash_code, SmallVector<Instruction *, 2>> OtherSuccessorsHash;
+  DenseMap<Instruction *, unsigned> InstToSkipFlag;
 
+  unsigned skipFlag = 0;
+  Instruction *I = nullptr;
+  do {
+    I = &*BBItrPair.first;
+    auto HashValue = getHash(I);
+    skipFlag |= skippedInstrFlags(I);
+    // For the first successor we created hashmap for, put all instructions
+    // in the hashmap execept for the ones that have the same hash as some
+    // previous instruction in that BB.
+    if (OtherSuccessorsHash.find(HashValue) == OtherSuccessorsHash.end()) {
+      OtherSuccessorsHash[HashValue] = {I};
+      InstToSkipFlag[I] = skipFlag;
+    }
+    BBItrPair.first++;
+  } while (!I->isTerminator());
+
+  unsigned Index = 1;
+  for (auto BBItrPair : OtherSuccIterPairRange) {
+    // Fill the hashmap for every other successor
+    unsigned skipFlag = 0;
+    Instruction *I = nullptr;
+    do {
+      I = &*BBItrPair.first;
+      auto HashValue = getHash(I);
+      skipFlag |= skippedInstrFlags(I);
+      auto &InstVec = OtherSuccessorsHash[HashValue];
+      // For other successors put the instrcution in the map only if there are
+      // instructions with the same hash from other successors and this is the
+      // first instruction with this hash value from current successor.
+      if (OtherSuccessorsHash.find(HashValue) != OtherSuccessorsHash.end() &&
+          InstVec.size() == Index) {
+        InstVec.push_back(I);
+        InstToSkipFlag[I] = skipFlag;
+      }
+      BBItrPair.first++;
+    } while (!I->isTerminator());
+    Index++;
+  }
+
+  // Keep track of instructions skipped in the first successor
+  unsigned SkipFlagsBB1 = 0;
+  bool SameLevelHoist = true;
   for (;;) {
     auto *SuccIterPairBegin = SuccIterPairs.begin();
     auto &BB1ItrPair = *SuccIterPairBegin++;
     auto OtherSuccIterPairRange =
         iterator_range(SuccIterPairBegin, SuccIterPairs.end());
     auto OtherSuccIterRange = make_first_range(OtherSuccIterPairRange);
-
     Instruction *I1 = &*BB1ItrPair.first;
 
     // Skip debug info if it is not identical.
-    bool AllDbgInstsAreIdentical = all_of(OtherSuccIterRange, [I1](auto &Iter) {
+    bool IdenticalDebugs = all_of(OtherSuccIterRange, [I1](auto &Iter) {
       Instruction *I2 = &*Iter;
       return I1->isIdenticalToWhenDefined(I2);
     });
-    if (!AllDbgInstsAreIdentical) {
+    if (!IdenticalDebugs) {
       while (isa<DbgInfoIntrinsic>(I1))
         I1 = &*++BB1ItrPair.first;
-      for (auto &SuccIter : OtherSuccIterRange) {
-        Instruction *I2 = &*SuccIter;
-        while (isa<DbgInfoIntrinsic>(I2))
-          I2 = &*++SuccIter;
-      }
     }
-
-    bool AllInstsAreIdentical = true;
-    bool HasTerminator = I1->isTerminator();
-    for (auto &SuccIter : OtherSuccIterRange) {
-      Instruction *I2 = &*SuccIter;
-      HasTerminator |= I2->isTerminator();
-      if (AllInstsAreIdentical && !I1->isIdenticalToWhenDefined(I2))
-        AllInstsAreIdentical = false;
+    auto OtherInsts = OtherSuccessorsHash[getHash(I1)];
----------------
nikic wrote:

```suggestion
    const auto &OtherInsts = OtherSuccessorsHash[getHash(I1)];
```

https://github.com/llvm/llvm-project/pull/78615