[clang] [llvm] [AMDGPU] Change CF intrinsics lowering to reconverge on predecessors. (PR #92809)

[Matt Arsenault via llvm-commits]

================
@@ -305,43 +304,43 @@ bool SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
 }
 
 /// Close the last opened control flow
-bool SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
-  llvm::Loop *L = LI->getLoopFor(BB);
+bool SIAnnotateControlFlow::tryWaveReconverge(BasicBlock *BB) {
 
-  assert(Stack.back().first == BB);
+  if (succ_empty(BB))
+    return false;
 
-  if (L && L->getHeader() == BB) {
-    // We can't insert an EndCF call into a loop header, because it will
-    // get executed on every iteration of the loop, when it should be
-    // executed only once before the loop.
-    SmallVector <BasicBlock *, 8> Latches;
-    L->getLoopLatches(Latches);
+  BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
+  if (Term->getNumSuccessors() == 1) {
+    // The current BBs single successor is a top of the stack. We need to
+    // reconverge over thaqt path.
+    BasicBlock *SingleSucc = *succ_begin(BB);
+    BasicBlock::iterator InsPt = Term ? BasicBlock::iterator(Term) : BB->end();
 
-    SmallVector<BasicBlock *, 2> Preds;
-    for (BasicBlock *Pred : predecessors(BB)) {
-      if (!is_contained(Latches, Pred))
-        Preds.push_back(Pred);
+    if (isTopOfStack(SingleSucc)) {
+      Value *Exec = Stack.back().second;
+      IRBuilder<>(BB, InsPt).CreateCall(WaveReconverge, {Exec});
     }
-
-    BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, nullptr,
-                                false);
-  }
-
-  Value *Exec = popSaved();
-  BasicBlock::iterator FirstInsertionPt = BB->getFirstInsertionPt();
-  if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt)) {
-    Instruction *ExecDef = cast<Instruction>(Exec);
-    BasicBlock *DefBB = ExecDef->getParent();
-    if (!DT->dominates(DefBB, BB)) {
-      // Split edge to make Def dominate Use
-      FirstInsertionPt = SplitEdge(DefBB, BB, DT, LI)->getFirstInsertionPt();
+  } else {
+    // We have a uniform conditional branch terminating the block.
+    // THis block may be the last in the Then path of the enclosing divergent
----------------
arsenm wrote:

Typo 'THis'

https://github.com/llvm/llvm-project/pull/92809