[NFC][LLVM][CodeGen] Refactor MIR Printer (#137361)

- Move `MIPrinter` class to anonymous namespace, and remove it as a
friend of `MachineBasicBlock`.
- Move `canPredictBranchProbabilities` to `MachineBasicBlock` and change
it to use the new `BranchProbability::normalizeProbabilities` function
that accepts a range, and also to use `llvm::equal()` to check equality
of the two vectors.
- Use `ListSeparator` to print comma separate lists instead of manual
code to do that.

1 files changed, 29 insertions, 13 deletions

diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index fa6b534..37fe37f 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -1587,20 +1587,36 @@ MachineBasicBlock::getSuccProbability(const_succ_iterator Succ) const {
     return BranchProbability(1, succ_size());
 
   const auto &Prob = *getProbabilityIterator(Succ);
-  if (Prob.isUnknown()) {
-    // For unknown probabilities, collect the sum of all known ones, and evenly
-    // ditribute the complemental of the sum to each unknown probability.
-    unsigned KnownProbNum = 0;
-    auto Sum = BranchProbability::getZero();
-    for (const auto &P : Probs) {
-      if (!P.isUnknown()) {
-        Sum += P;
-        KnownProbNum++;
-      }
-    }
-    return Sum.getCompl() / (Probs.size() - KnownProbNum);
-  } else
+  if (!Prob.isUnknown())
     return Prob;
+  // For unknown probabilities, collect the sum of all known ones, and evenly
+  // ditribute the complemental of the sum to each unknown probability.
+  unsigned KnownProbNum = 0;
+  auto Sum = BranchProbability::getZero();
+  for (const auto &P : Probs) {
+    if (!P.isUnknown()) {
+      Sum += P;
+      KnownProbNum++;
+    }
+  }
+  return Sum.getCompl() / (Probs.size() - KnownProbNum);
+}
+
+bool MachineBasicBlock::canPredictBranchProbabilities() const {
+  if (succ_size() <= 1)
+    return true;
+  if (!hasSuccessorProbabilities())
+    return true;
+
+  SmallVector<BranchProbability, 8> Normalized(Probs.begin(), Probs.end());
+  BranchProbability::normalizeProbabilities(Normalized);
+
+  // Normalize assuming unknown probabilities. This will assign equal
+  // probabilities to all successors.
+  SmallVector<BranchProbability, 8> Equal(Normalized.size());
+  BranchProbability::normalizeProbabilities(Equal);
+
+  return llvm::equal(Normalized, Equal);
 }
 
 /// Set successor probability of a given iterator.