[MLIR][LLVM] Fix inlining of a single block ending with unreachable

Author: wsmoses

mlir/examples/toy/Ch4/mlir/Dialect.cpp

@@ -73,7 +73,8 @@ struct ToyInlinerInterface : public DialectInlinerInterface {
 
   /// Handle the given inlined terminator(toy.return) by replacing it with a new
   /// operation as necessary.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {
     // Only "toy.return" needs to be handled here.
     auto returnOp = cast<ReturnOp>(op);
 

mlir/include/mlir/Transforms/InliningUtils.h

@@ -116,7 +116,7 @@ class DialectInlinerInterface
   /// calls, these are directly replaced with the operands of the `return`
   /// operation). The given 'op' will be removed by the caller, after this
   /// function has been called.
-  virtual void handleTerminator(Operation *op,
+  virtual void handleTerminator(Operation *op, OpBuilder &builder,
                                 ValueRange valuesToReplace) const {
     llvm_unreachable(
         "must implement handleTerminator in the case of one inlined block");
@@ -212,7 +212,8 @@ class InlinerInterface
   //===--------------------------------------------------------------------===//
 
   virtual void handleTerminator(Operation *op, Block *newDest) const;
-  virtual void handleTerminator(Operation *op, ValueRange valuesToRepl) const;
+  virtual void handleTerminator(Operation *op, OpBuilder &builder,
+                                ValueRange valuesToRepl) const;
 
   virtual Value handleArgument(OpBuilder &builder, Operation *call,
                                Operation *callable, Value argument,

mlir/lib/Dialect/Func/Extensions/InlinerExtension.cpp

@@ -67,7 +67,8 @@ struct FuncInlinerInterface : public DialectInlinerInterface {
 
   /// Handle the given inlined terminator by replacing it with a new operation
   /// as necessary.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {
     // Only return needs to be handled here.
     auto returnOp = cast<ReturnOp>(op);
 

mlir/lib/Dialect/LLVMIR/Transforms/InlinerInterfaceImpl.cpp

@@ -746,8 +746,17 @@ struct LLVMInlinerInterface : public DialectInlinerInterface {
   /// Handle the given inlined return by replacing the uses of the call with the
   /// operands of the return. This overload is called when the inlined region
   /// only contains one block.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {
-    // Return will be the only terminator present.
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {
+    if (isa<LLVM::UnreachableOp>(op)) {
+      for (auto dst : valuesToRepl) {
+        auto repl = builder.create<LLVM::UndefOp>(op->getLoc(), dst.getType());
+        dst.replaceAllUsesWith(repl);
+      }
+      return;
+    }
+
+    // Otherwise return will be the only terminator present.
     auto returnOp = cast<LLVM::ReturnOp>(op);
 
     // Replace the values directly with the return operands.

mlir/lib/Dialect/Linalg/IR/LinalgDialect.cpp

@@ -57,7 +57,8 @@ struct LinalgInlinerInterface : public DialectInlinerInterface {
   }
   // Handle the given inlined terminator by replacing it with a new operation
   // as necessary. Required when the region has only one block.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {}
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {}
 };
 
 } // namespace

mlir/lib/Dialect/SCF/IR/SCF.cpp

@@ -51,7 +51,8 @@ struct SCFInlinerInterface : public DialectInlinerInterface {
   }
   // Handle the given inlined terminator by replacing it with a new operation
   // as necessary. Required when the region has only one block.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {
     auto retValOp = dyn_cast<scf::YieldOp>(op);
     if (!retValOp)
       return;

mlir/lib/Dialect/SPIRV/IR/SPIRVDialect.cpp

@@ -103,7 +103,8 @@ struct SPIRVInlinerInterface : public DialectInlinerInterface {
 
   /// Handle the given inlined terminator by replacing it with a new operation
   /// as necessary.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {
     // Only spirv.ReturnValue needs to be handled here.
     auto retValOp = dyn_cast<spirv::ReturnValueOp>(op);
     if (!retValOp)

mlir/lib/Transforms/Utils/InliningUtils.cpp

@@ -111,11 +111,11 @@ void InlinerInterface::handleTerminator(Operation *op, Block *newDest) const {
 
 /// Handle the given inlined terminator by replacing it with a new operation
 /// as necessary.
-void InlinerInterface::handleTerminator(Operation *op,
+void InlinerInterface::handleTerminator(Operation *op, OpBuilder &builder,
                                         ValueRange valuesToRepl) const {
   auto *handler = getInterfaceFor(op);
   assert(handler && "expected valid dialect handler");
-  handler->handleTerminator(op, valuesToRepl);
+  handler->handleTerminator(op, builder, valuesToRepl);
 }
 
 Value InlinerInterface::handleArgument(OpBuilder &builder, Operation *call,
@@ -304,7 +304,7 @@ inlineRegionImpl(InlinerInterface &interface, Region *src, Block *inlineBlock,
                        firstBlockTerminator->getOperands());
 
     // Have the interface handle the terminator of this block.
-    interface.handleTerminator(firstBlockTerminator, resultsToReplace);
+    interface.handleTerminator(firstBlockTerminator, builder, resultsToReplace);
     firstBlockTerminator->erase();
 
     // Merge the post insert block into the cloned entry block.

mlir/test/Dialect/LLVMIR/inlining.mlir

@@ -676,3 +676,18 @@ llvm.func @caller(%x : i32) -> i32 {
   %z = llvm.call @private_func(%x) : (i32) -> (i32)
   llvm.return %z : i32
 }
+
+// -----
+
+llvm.func @unreachable_func(%a : i32) -> i32 {
+  "llvm.intr.trap"() : () -> ()
+  llvm.unreachable
+}
+
+// CHECK-LABEL: func @caller
+llvm.func @caller(%x : i32) -> i32 {
+  // CHECK-NOT: llvm.call @unreachable_func
+  // CHECK: llvm.intr.trap
+  %z = llvm.call @unreachable_func(%x) : (i32) -> (i32)
+  llvm.return %z : i32
+}

mlir/test/lib/Dialect/Test/TestDialectInterfaces.cpp

@@ -316,7 +316,8 @@ struct TestInlinerInterface : public DialectInlinerInterface {
 
   /// Handle the given inlined terminator by replacing it with a new operation
   /// as necessary.
-  void handleTerminator(Operation *op, ValueRange valuesToRepl) const final {
+  void handleTerminator(Operation *op, OpBuilder &builder,
+                        ValueRange valuesToRepl) const final {
     // Only handle "test.return" here.
     auto returnOp = dyn_cast<TestReturnOp>(op);
     if (!returnOp)