Address unrecheable block concerns

Author: bcardosolopes

mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

@@ -2302,19 +2302,31 @@ static LogicalResult verifyComdat(Operation *op,
 static LogicalResult verifyBlockTags(LLVMFuncOp funcOp) {
   llvm::DenseSet<BlockTagAttr> blockTags;
   BlockTagOp badBlockTagOp;
+  enum { DupTag, UnrecheableBlock } errorMsgType;
   if (funcOp
           .walk([&](BlockTagOp blockTagOp) {
+            mlir::Block *block = blockTagOp->getBlock();
+            if (!block->isEntryBlock() && block->use_empty()) {
+              badBlockTagOp = blockTagOp;
+              errorMsgType = UnrecheableBlock;
+              return WalkResult::interrupt();
+            }
+
             if (blockTags.contains(blockTagOp.getTag())) {
               badBlockTagOp = blockTagOp;
+              errorMsgType = DupTag;
               return WalkResult::interrupt();
             }
             blockTags.insert(blockTagOp.getTag());
             return WalkResult::advance();
           })
           .wasInterrupted()) {
-    badBlockTagOp.emitError()
-        << "duplicate block tag '" << badBlockTagOp.getTag().getId()
-        << "' in the same function: ";
+    if (errorMsgType == DupTag)
+      badBlockTagOp.emitError()
+          << "duplicate block tag '" << badBlockTagOp.getTag().getId()
+          << "' in the same function: ";
+    else
+      badBlockTagOp.emitError() << "not allowed in unrecheable blocks";
     return failure();
   }
 

mlir/test/Dialect/LLVMIR/blockaddress-canonicalize.mlir

@@ -1,4 +1,4 @@
-// RUN: mlir-opt %s -pass-pipeline='builtin.module(llvm.func(canonicalize{region-simplify=aggressive}))' -split-input-file | FileCheck %s
+// RUN: mlir-opt %s -pass-pipeline='builtin.module(llvm.func(canonicalize{region-simplify=aggressive}))' -verify-diagnostics -split-input-file | FileCheck %s
 
 llvm.mlir.global private @x() {addr_space = 0 : i32, dso_local} : !llvm.ptr {
   %0 = llvm.blockaddress <function = @ba, tag = <id = 2>> : !llvm.ptr
@@ -46,3 +46,27 @@ llvm.func @fn(%cond : i1, %arg0 : i32, %arg1 : i32) -> i32 {
   llvm.blocktag <id = 1>
   llvm.return %arg1 : i32
 }
+
+// -----
+
+llvm.mlir.global private @g() {addr_space = 0 : i32, dso_local} : !llvm.ptr {
+  %0 = llvm.blockaddress <function = @fn, tag = <id = 1>> : !llvm.ptr
+  llvm.return %0 : !llvm.ptr
+}
+
+// The Canonicalizer's region simplify pass can be hazardous when dealing
+// with indirect branches, as there is currently no mechanism to convey
+// dialect-specific block constraints.
+
+llvm.func @fn(%dest : !llvm.ptr, %arg0 : i32, %arg1 : i32) -> i32 {
+  llvm.indirectbr %dest : !llvm.ptr, [
+    ^head
+  ]
+^head:
+  llvm.blocktag <id = 0>
+  llvm.return %arg0 : i32
+^tail:
+  // expected-error@+1 {{not allowed in unrecheable blocks}}
+  llvm.blocktag <id = 1>
+  llvm.return %arg1 : i32
+}