[llvm] [SLU][profcheck] Estimate branch weights in partial unswitch cases (PR #164035)

[Mircea Trofin via llvm-commits]

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@@ -268,13 +275,40 @@ static bool areLoopExitPHIsLoopInvariant(const Loop &L,
   llvm_unreachable("Basic blocks should never be empty!");
 }
 
-/// Copy a set of loop invariant values \p ToDuplicate and insert them at the
+/// Copy a set of loop invariant values \p Invariants and insert them at the
 /// end of \p BB and conditionally branch on the copied condition. We only
 /// branch on a single value.
+/// We attempt to estimate the profile of the resulting conditional branch from
+/// \p ComputeProfFrom, which is the original conditional branch we're
+/// unswitching.
+/// When \p Direction is true, the \p Invariants form a disjunction, and the
+/// branch conditioned on it exits the loop on the "true" case. When \p
+/// Direction is false, the \p Invariants form a conjunction and the branch
+/// exits on the "false" case.
 static void buildPartialUnswitchConditionalBranch(
     BasicBlock &BB, ArrayRef<Value *> Invariants, bool Direction,
     BasicBlock &UnswitchedSucc, BasicBlock &NormalSucc, bool InsertFreeze,
-    const Instruction *I, AssumptionCache *AC, const DominatorTree &DT) {
+    const Instruction *I, AssumptionCache *AC, const DominatorTree &DT,
+    const BranchInst &ComputeProfFrom) {
+
+  SmallVector<uint32_t> BranchWeights;
+  bool HasBranchWeights = EstimateProfile && !ProfcheckDisableMetadataFixes &&
+                          extractBranchWeights(ComputeProfFrom, BranchWeights);
+  // If Direction is true, that means we had a disjunction and that the "true"
+  // Conversely, if Direction is false, that means we had a conjunction, and the
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mtrofin wrote:

probably stumbled on my fingers.

https://github.com/llvm/llvm-project/pull/164035