[CIR] Upstream StackSave and StackRestoreOp

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

@@ -1419,6 +1419,48 @@ def CallOp : CIR_CallOpBase<"call", [NoRegionArguments]> {
     }]>];
 }
 
+//===----------------------------------------------------------------------===//
+// StackSave & StackRestoreOp
+//===----------------------------------------------------------------------===//
+
+def StackSaveOp : CIR_Op<"stack_save"> {
+  let summary = "remembers the current state of the function stack";
+  let description = [{
+    Remembers the current state of the function stack. Returns a pointer
+    that later can be passed into cir.stack_restore.
+    Useful for implementing language features like variable length arrays.
+
+    ```mlir
+    %0 = cir.stack_save : <!u8i>
+    ```
+  }];
+
+  let results = (outs CIR_PointerType:$result);
+  let assemblyFormat = "attr-dict `:` qualified(type($result))";
+}
+
+def StackRestoreOp : CIR_Op<"stack_restore"> {
+  let summary = "restores the state of the function stack";
+  let description = [{
+    Restore the state of the function stack to the state it was
+    in when the corresponding cir.stack_save executed.
+    Useful for implementing language features like variable length arrays.
+
+    ```mlir
+    %0 = cir.alloca !cir.ptr<!u8i>, !cir.ptr<!cir.ptr<!u8i>>, ["saved_stack"] {alignment = 8 : i64}
+    %1 = cir.stack_save : <!u8i>
+    cir.store %1, %0 : !cir.ptr<!u8i>, !cir.ptr<!cir.ptr<!u8i>>
+    %2 = cir.load %0 : !cir.ptr<!cir.ptr<!u8i>>, !cir.ptr<!u8i>
+    cir.stack_restore %2 : !cir.ptr<!u8i>
+    ```
+  }];
+
+  let arguments = (ins CIR_PointerType:$ptr);
+  let assemblyFormat = "$ptr attr-dict `:` qualified(type($ptr))";
+
+  let llvmOp = "StackRestoreOp";
+}
+
 //===----------------------------------------------------------------------===//
 // UnreachableOp
 //===----------------------------------------------------------------------===//

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

@@ -1467,6 +1467,8 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                CIRToLLVMConstantOpLowering,
                CIRToLLVMFuncOpLowering,
                CIRToLLVMGetGlobalOpLowering,
+               CIRToLLVMStackSaveOpLowering,
+               CIRToLLVMStackRestoreOpLowering,
                CIRToLLVMTrapOpLowering,
                CIRToLLVMUnaryOpLowering
       // clang-format on
@@ -1512,6 +1514,22 @@ mlir::LogicalResult CIRToLLVMTrapOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+mlir::LogicalResult CIRToLLVMStackSaveOpLowering::matchAndRewrite(
+    cir::StackSaveOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  const mlir::Type ptrTy = getTypeConverter()->convertType(op.getType());
+  rewriter.replaceOpWithNewOp<mlir::LLVM::StackSaveOp>(op, ptrTy);
+  return mlir::success();
+}
+
+mlir::LogicalResult CIRToLLVMStackRestoreOpLowering::matchAndRewrite(
+    cir::StackRestoreOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  rewriter.replaceOpWithNewOp<mlir::LLVM::StackRestoreOp>(
+      op, adaptor.getOperands().front());
+  return mlir::success();
+}
+
 std::unique_ptr<mlir::Pass> createConvertCIRToLLVMPass() {
   return std::make_unique<ConvertCIRToLLVMPass>();
 }

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

@@ -242,6 +242,26 @@ class CIRToLLVMPtrStrideOpLowering
   matchAndRewrite(cir::PtrStrideOp op, OpAdaptor,
                   mlir::ConversionPatternRewriter &) const override;
 };
+
+class CIRToLLVMStackSaveOpLowering
+    : public mlir::OpConversionPattern<cir::StackSaveOp> {
+public:
+  using mlir::OpConversionPattern<cir::StackSaveOp>::OpConversionPattern;
+  mlir::LogicalResult
+  matchAndRewrite(cir::StackSaveOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
+class CIRToLLVMStackRestoreOpLowering
+    : public mlir::OpConversionPattern<cir::StackRestoreOp> {
+public:
+  using OpConversionPattern<cir::StackRestoreOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::StackRestoreOp op, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override;
+};
+
 } // namespace direct
 } // namespace cir
 

clang/test/CIR/IR/stack-save-restore.cir

@@ -0,0 +1,23 @@
+// Test the CIR operations can parse and print correctly (roundtrip)
+
+// RUN: cir-opt %s | cir-opt | FileCheck %s
+
+!u8i = !cir.int<u, 8>
+
+module  {
+  cir.func @stack_save_restore() {
+    %0 = cir.stack_save : !cir.ptr<!u8i>
+    cir.stack_restore %0 : !cir.ptr<!u8i>
+    cir.return
+  }
+}
+
+//CHECK: module  {
+
+//CHECK-NEXT: cir.func @stack_save_restore() {
+//CHECK-NEXT:   %0 = cir.stack_save : !cir.ptr<!u8i>
+//CHECK-NEXT:   cir.stack_restore %0 : !cir.ptr<!u8i>
+//CHECK-NEXT:   cir.return
+//CHECK-NEXT: }
+
+//CHECK-NEXT: }

clang/test/CIR/Lowering/stack-save-restore.cir

@@ -0,0 +1,19 @@
+// RUN: cir-opt %s -cir-to-llvm -o - | FileCheck %s -check-prefix=MLIR
+
+!u8i = !cir.int<u, 8>
+
+module  {
+  cir.func @stack_save() {
+    %0 = cir.stack_save : !cir.ptr<!u8i>
+    cir.stack_restore %0 : !cir.ptr<!u8i>
+    cir.return
+  }
+}
+
+//      MLIR: module {
+// MLIR-NEXT:  llvm.func @stack_save
+// MLIR-NEXT:    %0 = llvm.intr.stacksave : !llvm.ptr
+// MLIR-NEXT:    llvm.intr.stackrestore %0 : !llvm.ptr
+// MLIR-NEXT:    llvm.return
+// MLIR-NEXT:  }
+// MLIR-NEXT: }