[clang] [CIR] Upstream Exception EhInflight op (PR #165621)

[Amr Hesham via cfe-commits]

https://github.com/AmrDeveloper created https://github.com/llvm/llvm-project/pull/165621

Upstream Exception EhInflight op as a prerequisite for full catch handlers implementation

Issue https://github.com/llvm/llvm-project/issues/154992

>From 111e875d665782a7dec55d4fd486a7852c8ea164 Mon Sep 17 00:00:00 2001
From: Amr Hesham <amr96 at programmer.net>
Date: Wed, 29 Oct 2025 21:01:11 +0100
Subject: [PATCH] [CIR] Upstream Exception EhInflight op

---
 clang/include/clang/CIR/Dialect/IR/CIROps.td  | 29 +++++++
 .../CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp | 82 +++++++++++++++++++
 clang/test/CIR/IR/eh-inflight.cir             | 15 ++++
 3 files changed, 126 insertions(+)
 create mode 100644 clang/test/CIR/IR/eh-inflight.cir

diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 2b361ed0982c6..0497d97239000 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -4490,6 +4490,35 @@ def CIR_TryOp : CIR_Op<"try",[
   let hasLLVMLowering = false;
 }
 
+//===----------------------------------------------------------------------===//
+// Exception related: EhInflightOp
+//===----------------------------------------------------------------------===//
+
+def CIR_EhInflightOp : CIR_Op<"eh.inflight_exception"> {
+  let summary = "Materialize the catch clause formal parameter";
+  let description = [{
+    `cir.eh.inflight_exception` returns two values:
+      - `exception_ptr`: The exception pointer for the inflight exception
+      - `type_id`: pointer to the exception object
+    This operation is expected to be the first one basic blocks on the
+    exception path out of `cir.try_call` operations.
+
+    The `cleanup` attribute indicates that clean up code might run before the
+    values produced by this operation are used to gather exception information.
+    This helps CIR to pass down more accurate information for LLVM lowering
+    to landingpads.
+  }];
+
+  let arguments = (ins UnitAttr:$cleanup,
+                       OptionalAttr<FlatSymbolRefArrayAttr>:$sym_type_list);
+  let results = (outs CIR_VoidPtrType:$exception_ptr, CIR_UInt32:$type_id);
+  let assemblyFormat = [{
+    (`cleanup` $cleanup^)?
+    ($sym_type_list^)?
+    attr-dict
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // Atomic operations
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index 5a6193fa8d840..0bf5eb740096f 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -3002,6 +3002,88 @@ mlir::LogicalResult CIRToLLVMAllocExceptionOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+static mlir::LLVM::LLVMStructType
+getLLVMLandingPadStructTy(mlir::ConversionPatternRewriter &rewriter) {
+  // Create the landing pad type: struct { ptr, i32 }
+  mlir::MLIRContext *ctx = rewriter.getContext();
+  auto llvmPtr = mlir::LLVM::LLVMPointerType::get(ctx);
+  llvm::SmallVector<mlir::Type> structFields = {llvmPtr, rewriter.getI32Type()};
+  return mlir::LLVM::LLVMStructType::getLiteral(ctx, structFields);
+}
+
+mlir::LogicalResult CIRToLLVMEhInflightOpLowering::matchAndRewrite(
+    cir::EhInflightOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto llvmFn = op->getParentOfType<mlir::LLVM::LLVMFuncOp>();
+  assert(llvmFn && "expected LLVM function parent");
+  mlir::Block *entryBlock = &llvmFn.getRegion().front();
+  assert(entryBlock->isEntryBlock());
+
+  mlir::ArrayAttr symListAttr = op.getSymTypeListAttr();
+  mlir::SmallVector<mlir::Value, 4> symAddrs;
+
+  auto llvmPtrTy = mlir::LLVM::LLVMPointerType::get(rewriter.getContext());
+  mlir::Location loc = op.getLoc();
+
+  // %landingpad = landingpad { ptr, i32 }
+  // Note that since llvm.landingpad has to be the first operation on the
+  // block, any needed value for its operands has to be added somewhere else.
+  if (symListAttr) {
+    //   catch ptr @_ZTIi
+    //   catch ptr @_ZTIPKc
+    for (mlir::Attribute attr : symListAttr) {
+      auto symAttr = cast<mlir::FlatSymbolRefAttr>(attr);
+      // Generate `llvm.mlir.addressof` for each symbol, and place those
+      // operations in the LLVM function entry basic block.
+      mlir::OpBuilder::InsertionGuard guard(rewriter);
+      rewriter.setInsertionPointToStart(entryBlock);
+      mlir::Value addrOp = mlir::LLVM::AddressOfOp::create(
+          rewriter, loc, llvmPtrTy, symAttr.getValue());
+      symAddrs.push_back(addrOp);
+    }
+  } else if (!op.getCleanup()) {
+    // catch ptr null
+    mlir::OpBuilder::InsertionGuard guard(rewriter);
+    rewriter.setInsertionPointToStart(entryBlock);
+    mlir::Value nullOp = mlir::LLVM::ZeroOp::create(rewriter, loc, llvmPtrTy);
+    symAddrs.push_back(nullOp);
+  }
+
+  // %slot = extractvalue { ptr, i32 } %x, 0
+  // %selector = extractvalue { ptr, i32 } %x, 1
+  mlir::LLVM::LLVMStructType llvmLandingPadStructTy =
+      getLLVMLandingPadStructTy(rewriter);
+  auto landingPadOp = mlir::LLVM::LandingpadOp::create(
+      rewriter, loc, llvmLandingPadStructTy, symAddrs);
+
+  if (op.getCleanup())
+    landingPadOp.setCleanup(true);
+
+  mlir::Value slot =
+      mlir::LLVM::ExtractValueOp::create(rewriter, loc, landingPadOp, 0);
+  mlir::Value selector =
+      mlir::LLVM::ExtractValueOp::create(rewriter, loc, landingPadOp, 1);
+  rewriter.replaceOp(op, mlir::ValueRange{slot, selector});
+
+  // Landing pads are required to be in LLVM functions with personality
+  // attribute.
+  // TODO(cir): for now hardcode personality creation in order to start
+  // adding exception tests, once we annotate CIR with such information,
+  // change it to be in FuncOp lowering instead.
+  mlir::OpBuilder::InsertionGuard guard(rewriter);
+  // Insert personality decl before the current function.
+  rewriter.setInsertionPoint(llvmFn);
+  auto personalityFnTy =
+      mlir::LLVM::LLVMFunctionType::get(rewriter.getI32Type(), {},
+                                        /*isVarArg=*/true);
+  // Get or create `__gxx_personality_v0`
+  const StringRef fnName = "__gxx_personality_v0";
+  createLLVMFuncOpIfNotExist(rewriter, op, fnName, personalityFnTy);
+  llvmFn.setPersonality(fnName);
+
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRToLLVMTrapOpLowering::matchAndRewrite(
     cir::TrapOp op, OpAdaptor adaptor,
     mlir::ConversionPatternRewriter &rewriter) const {
diff --git a/clang/test/CIR/IR/eh-inflight.cir b/clang/test/CIR/IR/eh-inflight.cir
new file mode 100644
index 0000000000000..90a5f3f67b6fe
--- /dev/null
+++ b/clang/test/CIR/IR/eh-inflight.cir
@@ -0,0 +1,15 @@
+// RUN: cir-opt %s --verify-roundtrip | FileCheck %s
+
+module {
+
+cir.func dso_local @function_with_inflight_exception() {
+  %exception_ptr, %type_id = cir.eh.inflight_exception
+  cir.return
+}
+
+// CHECK: cir.func dso_local @function_with_inflight_exception() {
+// CHECK:  %exception_ptr, %type_id = cir.eh.inflight_exception
+// CHECK:  cir.return
+// CHECK: }
+
+}