[CIR][CIRGen] Exceptions: support free'ing allocated exception resources

Author: bcardosolopes

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -4092,7 +4092,7 @@ def VAArgOp : CIR_Op<"va.arg">,
 }
 
 //===----------------------------------------------------------------------===//
-// AllocExceptionOp
+// AllocExceptionOp & FreeExceptionOp
 //===----------------------------------------------------------------------===//
 
 def AllocExceptionOp : CIR_Op<"alloc.exception"> {
@@ -4129,6 +4129,39 @@ def AllocExceptionOp : CIR_Op<"alloc.exception"> {
   let hasVerifier = 0;
 }
 
+def FreeExceptionOp : CIR_Op<"free.exception"> {
+  let summary = "Frees an exception according to Itanium ABI";
+  let description = [{
+    Implements a slightly higher level version of:
+    `void __cxa_free_exception(void *thrown_exception);`
+
+    Example:
+
+    ```mlir
+    %0 = cir.alloc.exception 16 -> !cir.ptr<!some_struct>
+    %1 = cir.get_global @d2 : !cir.ptr<!some_struct>
+    cir.try synthetic cleanup {
+      cir.call exception @_ZN7test2_DC1ERKS_(%0, %1) : (!cir.ptr<!some_struct>, !cir.ptr<!some_struct>) -> () cleanup {
+        %2 = cir.cast(bitcast, %0 : !cir.ptr<!some_struct>), !cir.ptr<!void>
+        cir.free.exception %2
+        cir.yield
+      }
+      ...
+    }
+    ```
+  }];
+
+  let arguments = (ins VoidPtr:$ptr);
+  let results = (outs);
+
+  let assemblyFormat = [{
+    $ptr attr-dict
+  }];
+
+  // Constraints already described.
+  let hasVerifier = 0;
+}
+
 //===----------------------------------------------------------------------===//
 // ThrowOp
 //===----------------------------------------------------------------------===//

clang/lib/CIR/CodeGen/CIRGenException.cpp

@@ -214,7 +214,12 @@ struct FreeException final : EHScopeStack::Cleanup {
   mlir::Value exn;
   FreeException(mlir::Value exn) : exn(exn) {}
   void Emit(CIRGenFunction &CGF, Flags flags) override {
-    llvm_unreachable("call to cxa_free or equivalent op NYI");
+    // OG LLVM codegen emits a no unwind call, CIR emits an operation.
+    cir::CIRGenBuilderTy &builder = CGF.getBuilder();
+    mlir::Location loc =
+        CGF.currSrcLoc ? *CGF.currSrcLoc : builder.getUnknownLoc();
+    builder.create<mlir::cir::FreeExceptionOp>(
+        loc, builder.createBitcast(exn, builder.getVoidPtrTy()));
   }
 };
 } // end anonymous namespace

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -3788,6 +3788,27 @@ class CIRAllocExceptionOpLowering
   }
 };
 
+class CIRFreeExceptionOpLowering
+    : public mlir::OpConversionPattern<mlir::cir::FreeExceptionOp> {
+public:
+  using OpConversionPattern<mlir::cir::FreeExceptionOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(mlir::cir::FreeExceptionOp op, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    // Get or create `declare void @__cxa_free_exception(ptr)`
+    StringRef fnName = "__cxa_free_exception";
+    auto llvmPtrTy = mlir::LLVM::LLVMPointerType::get(rewriter.getContext());
+    auto voidTy = mlir::LLVM::LLVMVoidType::get(rewriter.getContext());
+    auto fnTy = mlir::LLVM::LLVMFunctionType::get(voidTy, {llvmPtrTy},
+                                                  /*isVarArg=*/false);
+    getOrCreateLLVMFuncOp(rewriter, op, fnName, fnTy);
+    rewriter.replaceOpWithNewOp<mlir::LLVM::CallOp>(
+        op, mlir::TypeRange{}, fnName, mlir::ValueRange{adaptor.getPtr()});
+    return mlir::success();
+  }
+};
+
 class CIRThrowOpLowering
     : public mlir::OpConversionPattern<mlir::cir::ThrowOp> {
 public:
@@ -3854,8 +3875,8 @@ void populateCIRToLLVMConversionPatterns(mlir::RewritePatternSet &patterns,
       CIRPrefetchLowering, CIRObjSizeOpLowering, CIRIsConstantOpLowering,
       CIRCmpThreeWayOpLowering, CIRClearCacheOpLowering, CIRUndefOpLowering,
       CIREhTypeIdOpLowering, CIRCatchParamOpLowering, CIRResumeOpLowering,
-      CIRAllocExceptionOpLowering, CIRThrowOpLowering, CIRIntrinsicCallLowering,
-      CIRBaseClassAddrOpLowering
+      CIRAllocExceptionOpLowering, CIRFreeExceptionOpLowering,
+      CIRThrowOpLowering, CIRIntrinsicCallLowering, CIRBaseClassAddrOpLowering
 #define GET_BUILTIN_LOWERING_LIST
 #include "clang/CIR/Dialect/IR/CIRBuiltinsLowering.inc"
 #undef GET_BUILTIN_LOWERING_LIST

clang/test/CIR/CodeGen/eh.cpp

@@ -26,4 +26,41 @@ void test1() {
 // LLVM:   call void @_ZN7test1_DC1ERKS_(ptr %[[ALLOC]], ptr @d1)
 // LLVM:   call void @__cxa_throw(ptr %[[ALLOC]], ptr @_ZTI7test1_D, ptr null)
 // LLVM:   unreachable
-// LLVM: }
+// LLVM: }
+
+struct test2_D {
+  test2_D(const test2_D&o);
+  test2_D();
+  virtual void bar() { }
+  int i; int j;
+} d2;
+
+void test2() {
+  throw d2;
+}
+
+// CIR-LABEL: @_Z5test2v
+// CIR:   %[[ALLOC:.*]] = cir.alloc.exception 16 -> !cir.ptr<!ty_test2_D>
+// CIR:   %[[G:.*]] = cir.get_global @d2 : !cir.ptr<!ty_test2_D>
+// CIR:   cir.try synthetic cleanup {
+// CIR:     cir.call exception @_ZN7test2_DC1ERKS_(%[[ALLOC]], %[[G]]) : (!cir.ptr<!ty_test2_D>, !cir.ptr<!ty_test2_D>) -> () cleanup {
+// CIR:       %[[VOID_PTR:.*]] = cir.cast(bitcast, %[[ALLOC]] : !cir.ptr<!ty_test2_D>), !cir.ptr<!void>
+// CIR:       cir.free.exception %[[VOID_PTR]]
+// CIR:       cir.yield
+// CIR:     }
+// CIR:     cir.yield
+// CIR:   } catch [#cir.unwind {
+// CIR:     cir.resume
+// CIR:   }]
+// CIR:   cir.throw %[[ALLOC]] : !cir.ptr<!ty_test2_D>, @_ZTI7test2_D
+// CIR:   cir.unreachable
+
+// LLVM-LABEL: @_Z5test2v
+
+// LLVM: %[[ALLOC:.*]] = call ptr @__cxa_allocate_exception(i64 16)
+
+// LLVM: landingpad { ptr, i32 }
+// LLVM:         cleanup
+// LLVM: extractvalue { ptr, i32 }
+// LLVM: extractvalue { ptr, i32 }
+// LLVM: call void @__cxa_free_exception(ptr %[[ALLOC]])