[flang-commits] [flang] [mlir] [flang][OpenMP] Allow saving first block of an OMP region for allocas (PR #121886)

[Tom Eccles via flang-commits]

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@@ -345,31 +345,37 @@ findAllocaInsertPoint(llvm::IRBuilderBase &builder,
         allocaInsertPoint = frame.allocaInsertPoint;
         return WalkResult::interrupt();
       });
-  if (walkResult.wasInterrupted())
-    return allocaInsertPoint;
 
   // Otherwise, insert to the entry block of the surrounding function.
-  // If the current IRBuilder InsertPoint is the function's entry, it cannot
-  // also be used for alloca insertion which would result in insertion order
-  // confusion. Create a new BasicBlock for the Builder and use the entry block
-  // for the allocs.
+  if (!walkResult.wasInterrupted()) {
+    llvm::BasicBlock &funcEntryBlock =
+        builder.GetInsertBlock()->getParent()->getEntryBlock();
+    allocaInsertPoint = llvm::OpenMPIRBuilder::InsertPointTy(
+        &funcEntryBlock, funcEntryBlock.getFirstInsertionPt());
+  }
+
+  // If the current IRBuilder insertion block is the same as the alloca
+  // insertion block, it cannot also be used for alloca insertion which would
+  // result in insertion order confusion. Create a new BasicBlock for the
+  // Builder and use the entry block for the allocs.
+  //
   // TODO: Create a dedicated alloca BasicBlock at function creation such that
   // we do not need to move the current InertPoint here.
-  if (builder.GetInsertBlock() ==
-      &builder.GetInsertBlock()->getParent()->getEntryBlock()) {
+  if (builder.GetInsertBlock() == allocaInsertPoint.getBlock()) {
     assert(builder.GetInsertPoint() == builder.GetInsertBlock()->end() &&
            "Assuming end of basic block");
-    llvm::BasicBlock *entryBB = llvm::BasicBlock::Create(
-        builder.getContext(), "entry", builder.GetInsertBlock()->getParent(),
-        builder.GetInsertBlock()->getNextNode());
-    builder.CreateBr(entryBB);
-    builder.SetInsertPoint(entryBB);
+    auto *insertCont = splitBB(
+        llvm::OpenMPIRBuilder::InsertPointTy(
+            allocaInsertPoint.getBlock(), allocaInsertPoint.getBlock()->end()),
+        true, "insert.cont");
+    builder.SetInsertPoint(insertCont, insertCont->end());
   }
 
-  llvm::BasicBlock &funcEntryBlock =
-      builder.GetInsertBlock()->getParent()->getEntryBlock();
   return llvm::OpenMPIRBuilder::InsertPointTy(
-      &funcEntryBlock, funcEntryBlock.getFirstInsertionPt());
+      allocaInsertPoint.getBlock(),
+      allocaInsertPoint.getPoint() != allocaInsertPoint.getBlock()->end()
+          ? allocaInsertPoint.getPoint()
+          : allocaInsertPoint.getBlock()->getFirstInsertionPt());
----------------
tblah wrote:

Why not unconditionally put the alloca at the start of the block?

https://github.com/llvm/llvm-project/pull/121886