[llvm] [VPlan] Add initial CFG simplification, removing BranchOnCond true. (PR #106748)

[Florian Hahn via llvm-commits]

================
@@ -3527,12 +3527,20 @@ class VPlan {
 
   /// Returns the 'middle' block of the plan, that is the block that selects
   /// whether to execute the scalar tail loop or the exit block from the loop
-  /// latch.
-  const VPBasicBlock *getMiddleBlock() const {
-    return cast<VPBasicBlock>(getScalarPreheader()->getPredecessors().front());
-  }
+  /// latch. If the scalar tail loop or exit block are known to always execute,
+  /// the middle block may branch directly to the block.
   VPBasicBlock *getMiddleBlock() {
-    return cast<VPBasicBlock>(getScalarPreheader()->getPredecessors().front());
+    VPRegionBlock *LoopRegion = getVectorLoopRegion();
+    if (!LoopRegion)
+      return nullptr;
+    auto *RegionSucc = LoopRegion->getSingleSuccessor();
+    if (RegionSucc->getSingleSuccessor() ||
+        is_contained(RegionSucc->getSuccessors(), getScalarPreheader()))
+      return cast<VPBasicBlock>(RegionSucc);
+    return cast<VPBasicBlock>(RegionSucc->getSuccessors()[1]);
+  }
+  const VPBasicBlock *getMiddleBlock() const {
----------------
fhahn wrote:

Done thanks

https://github.com/llvm/llvm-project/pull/106748