[CIR] Upstream __builtin_va_start and __builtin_va_end #153819

mmha · 2025-08-15T15:19:14Z

Part of #153286

llvmbot · 2025-08-15T15:19:46Z

@llvm/pr-subscribers-clangir

Author: Morris Hafner (mmha)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/153819.diff

8 Files Affected:

(modified) clang/include/clang/CIR/Dialect/IR/CIROps.td (+77)
(modified) clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp (+21)
(modified) clang/lib/CIR/CodeGen/CIRGenExpr.cpp (+2-5)
(modified) clang/lib/CIR/CodeGen/CIRGenFunction.cpp (+6)
(modified) clang/lib/CIR/CodeGen/CIRGenFunction.h (+13)
(modified) clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp (+22)
(modified) clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h (+20)
(added) clang/test/CIR/CodeGen/var_arg.c (+48)

diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index a77e9199cdc96..86c8b59bf36f0 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -3415,4 +3415,81 @@ def CIR_FAbsOp : CIR_UnaryFPToFPBuiltinOp<"fabs", "FAbsOp"> {
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// Variadic Operations
+//===----------------------------------------------------------------------===//
+
+def CIR_VAStartOp : CIR_Op<"va.start"> {
+  let summary = "Starts a variable argument list";
+  let description = [{
+    The cir.va.start operation models the C/C++ va_start macro by
+    initializing a variable argument list at the given va_list storage
+    location.
+
+    The operand must be a pointer to the target's `va_list` representation.
+    This operation has no results and produces its effect by mutating the
+    storage referenced by the pointer operand.
+
+    Each `cir.va.start` must be paired with a corresponding `cir.va.end`
+    on the same logical `va_list` object along all control-flow paths. After
+    `cir.va.end`, the `va_list` must not be accessed unless reinitialized
+    with another `cir.va.start`.
+
+    Lowering typically maps this to the LLVM intrinsic `llvm.va_start`,
+    passing the appropriately decayed pointer to the underlying `va_list`
+    storage.
+
+    Example:
+
+    ```mlir
+    // %args : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>
+    %p = cir.cast(array_to_ptrdecay, %args
+          : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>),
+        !cir.ptr<!rec___va_list_tag>
+    cir.va.start %p : !cir.ptr<!rec___va_list_tag>
+    ```
+  }];
+  let arguments = (ins CIR_PointerType:$arg_list);
+
+  let assemblyFormat = [{
+    $arg_list attr-dict `:` type(operands)
+  }];
+}
+
+def CIR_VAEndOp : CIR_Op<"va.end"> {
+  let summary = "Ends a variable argument list";
+  let description = [{
+    The `cir.va.end` operation models the C/C++ va_end macro by finalizing
+    and cleaning up a variable argument list previously initialized with
+    `cir.va.start`.
+
+    The operand must be a pointer to the target's `va_list` representation.
+    This operation has no results and produces its effect by mutating the
+    storage referenced by the pointer operand.
+
+    `cir.va.end` must only be called after a matching `cir.va.start` on the
+    same `va_list` along all control-flow paths. After `cir.va.end`, the
+    `va_list` is invalid and must not be accessed unless reinitialized.
+
+    Lowering typically maps this to the LLVM intrinsic `llvm.va_end`,
+    passing the appropriately decayed pointer to the underlying `va_list`
+    storage.
+
+    Example:
+    ```mlir
+    // %args : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>
+    %p = cir.cast(array_to_ptrdecay, %args
+          : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>),
+        !cir.ptr<!rec___va_list_tag>
+    cir.va.end %p : !cir.ptr<!rec___va_list_tag>
+    ```
+  }];
+
+  let arguments = (ins CIR_PointerType:$arg_list);
+
+  let assemblyFormat = [{
+    $arg_list attr-dict `:` type(operands)
+  }];
+}
+
 #endif // CLANG_CIR_DIALECT_IR_CIROPS_TD
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 36aea4c1d39ce..25ca10e801194 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -125,6 +125,18 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
   default:
     break;
 
+  // C stdarg builtins.
+  case Builtin::BI__builtin_stdarg_start:
+  case Builtin::BI__builtin_va_start:
+  case Builtin::BI__va_start:
+  case Builtin::BI__builtin_va_end: {
+    emitVAStartEnd(builtinID == Builtin::BI__va_start
+                       ? emitScalarExpr(e->getArg(0))
+                       : emitVAListRef(e->getArg(0)).getPointer(),
+                   builtinID != Builtin::BI__builtin_va_end);
+    return {};
+  }
+
   case Builtin::BIfabs:
   case Builtin::BIfabsf:
   case Builtin::BIfabsl:
@@ -361,3 +373,12 @@ mlir::Value CIRGenFunction::emitCheckedArgForAssume(const Expr *e) {
                "emitCheckedArgForAssume: sanitizers are NYI");
   return {};
 }
+
+void CIRGenFunction::emitVAStartEnd(mlir::Value argValue, bool isStart) {
+  // LLVM codegen casts to *i8, no real gain on doing this for CIRGen this
+  // early, defer to LLVM lowering.
+  if (isStart)
+    cir::VAStartOp::create(builder, argValue.getLoc(), argValue);
+  else
+    cir::VAEndOp::create(builder, argValue.getLoc(), argValue);
+}
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
index 8bcca6f5d1803..00f2a64281b8c 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -90,11 +90,8 @@ Address CIRGenFunction::emitPointerWithAlignment(const Expr *expr,
     } break;
 
     // Array-to-pointer decay. TODO(cir): BaseInfo and TBAAInfo.
-    case CK_ArrayToPointerDecay: {
-      cgm.errorNYI(expr->getSourceRange(),
-                   "emitPointerWithAlignment: array-to-pointer decay");
-      return Address::invalid();
-    }
+    case CK_ArrayToPointerDecay:
+      return emitArrayToPointerDecay(ce->getSubExpr());
 
     case CK_UncheckedDerivedToBase:
     case CK_DerivedToBase: {
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.cpp b/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
index d6a0792292604..917afa8e78021 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
@@ -1080,4 +1080,10 @@ void CIRGenFunction::emitVariablyModifiedType(QualType type) {
   } while (type->isVariablyModifiedType());
 }
 
+Address CIRGenFunction::emitVAListRef(const Expr *e) {
+  if (getContext().getBuiltinVaListType()->isArrayType())
+    return emitPointerWithAlignment(e);
+  return emitLValue(e).getAddress();
+}
+
 } // namespace clang::CIRGen
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
index 9a887ec047f86..1c89c2c9d57d3 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.h
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -1411,6 +1411,19 @@ class CIRGenFunction : public CIRGenTypeCache {
                                     const clang::Stmt *thenS,
                                     const clang::Stmt *elseS);
 
+  /// Build a "reference" to a va_list; this is either the address or the value
+  /// of the expression, depending on how va_list is defined.
+  Address emitVAListRef(const Expr *e);
+
+  /// Emits a CIR variable-argument operation, either
+  /// \c cir.va.start or \c cir.va.end.
+  ///
+  /// \param argValue A reference to the \c va_list as emitted by either
+  /// \c emitVAListRef or \c emitMSVAListRef.
+  ///
+  /// \param isStart If \c true, emits \c cir.va.start, otherwise \c cir.va.end.
+  void emitVAStartEnd(mlir::Value argValue, bool isStart);
+
   /// ----------------------
   /// CIR build helpers
   /// -----------------
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index 1ea296a6887ef..e51fbc9eadaf0 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -2336,6 +2336,8 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                CIRToLLVMTrapOpLowering,
                CIRToLLVMUnaryOpLowering,
                CIRToLLVMUnreachableOpLowering,
+               CIRToLLVMVAEndOpLowering,
+               CIRToLLVMVAStartOpLowering,
                CIRToLLVMVecCmpOpLowering,
                CIRToLLVMVecCreateOpLowering,
                CIRToLLVMVecExtractOpLowering,
@@ -3035,6 +3037,26 @@ mlir::LogicalResult CIRToLLVMInlineAsmOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+mlir::LogicalResult CIRToLLVMVAStartOpLowering::matchAndRewrite(
+    cir::VAStartOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto opaquePtr = mlir::LLVM::LLVMPointerType::get(getContext());
+  auto vaList = mlir::LLVM::BitcastOp::create(rewriter, op.getLoc(), opaquePtr,
+                                              adaptor.getArgList());
+  rewriter.replaceOpWithNewOp<mlir::LLVM::VaStartOp>(op, vaList);
+  return mlir::success();
+}
+
+mlir::LogicalResult CIRToLLVMVAEndOpLowering::matchAndRewrite(
+    cir::VAEndOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto opaquePtr = mlir::LLVM::LLVMPointerType::get(getContext());
+  auto vaList = mlir::LLVM::BitcastOp::create(rewriter, op.getLoc(), opaquePtr,
+                                              adaptor.getArgList());
+  rewriter.replaceOpWithNewOp<mlir::LLVM::VaEndOp>(op, vaList);
+  return mlir::success();
+}
+
 std::unique_ptr<mlir::Pass> createConvertCIRToLLVMPass() {
   return std::make_unique<ConvertCIRToLLVMPass>();
 }
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
index e32bf2d1bae0c..72315ac127e1b 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
@@ -684,6 +684,26 @@ class CIRToLLVMInlineAsmOpLowering
                   mlir::ConversionPatternRewriter &) const override;
 };
 
+class CIRToLLVMVAStartOpLowering
+    : public mlir::OpConversionPattern<cir::VAStartOp> {
+public:
+  using mlir::OpConversionPattern<cir::VAStartOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::VAStartOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
+class CIRToLLVMVAEndOpLowering
+    : public mlir::OpConversionPattern<cir::VAEndOp> {
+public:
+  using mlir::OpConversionPattern<cir::VAEndOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::VAEndOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
 } // namespace direct
 } // namespace cir
 
diff --git a/clang/test/CIR/CodeGen/var_arg.c b/clang/test/CIR/CodeGen/var_arg.c
new file mode 100644
index 0000000000000..7cd10e1ca42d2
--- /dev/null
+++ b/clang/test/CIR/CodeGen/var_arg.c
@@ -0,0 +1,48 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+void varargs(int count, ...) {
+    __builtin_va_list args;
+    __builtin_va_start(args, 12345);
+    __builtin_va_end(args);
+}
+
+// CIR: !rec___va_list_tag = !cir.record<struct "__va_list_tag" {!u32i, !u32i, !cir.ptr<!void>, !cir.ptr<!void>}
+
+// CIR: cir.func dso_local @varargs(%[[COUNT_ARG:.+]]: !s32i {{.*}}, ...) {{.*}}
+// CIR:   %[[COUNT:.+]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["count", init]
+// CIR:   %[[ARGS:.+]]  = cir.alloca !cir.array<!rec___va_list_tag x 1>, !cir.ptr<!cir.array<!rec___va_list_tag x 1>>, ["args"]
+// CIR:   cir.store %[[COUNT_ARG]], %[[COUNT]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[ARGS_DECAY1:.+]] = cir.cast(array_to_ptrdecay, %[[ARGS]] : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>), !cir.ptr<!rec___va_list_tag>
+// CIR:   cir.va.start %[[ARGS_DECAY1]] : !cir.ptr<!rec___va_list_tag>
+// CIR:   %[[ARGS_DECAY2:.+]] = cir.cast(array_to_ptrdecay, %[[ARGS]] : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>), !cir.ptr<!rec___va_list_tag>
+// CIR:   cir.va.end %[[ARGS_DECAY2]] : !cir.ptr<!rec___va_list_tag>
+// CIR:   cir.return
+
+// LLVM: %struct.__va_list_tag = type { i32, i32, ptr, ptr }
+
+// LLVM: define dso_local void @varargs(i32 %[[ARG0:.+]], ...)
+// LLVM:   %[[COUNT_ADDR:.+]] = alloca i32, i64 1
+// LLVM:   %[[ARGS:.+]] = alloca [1 x %struct.__va_list_tag], i64 1
+// LLVM:   store i32 %[[ARG0]], ptr %[[COUNT_ADDR]]
+// LLVM:   %[[GEP1:.+]] = getelementptr %struct.__va_list_tag, ptr %[[ARGS]], i32 0
+// LLVM:   call void @llvm.va_start.p0(ptr %[[GEP1]])
+// LLVM:   %[[GEP2:.+]] = getelementptr %struct.__va_list_tag, ptr %[[ARGS]], i32 0
+// LLVM:   call void @llvm.va_end.p0(ptr %[[GEP2]])
+// LLVM:   ret void
+
+// OGCG: %struct.__va_list_tag = type { i32, i32, ptr, ptr }
+
+// OGCG: define dso_local void @varargs(i32 noundef %[[COUNT:.+]], ...)
+// OGCG:   %[[COUNT_ADDR:.+]] = alloca i32
+// OGCG:   %[[ARGS:.+]] = alloca [1 x %struct.__va_list_tag]
+// OGCG:   store i32 %[[COUNT]], ptr %[[COUNT_ADDR]]
+// OGCG:   %[[ARRDECAY1:.+]] = getelementptr inbounds [1 x %struct.__va_list_tag], ptr %[[ARGS]], i64 0, i64 0
+// OGCG:   call void @llvm.va_start.p0(ptr %[[ARRDECAY1]])
+// OGCG:   %[[ARRDECAY2:.+]] = getelementptr inbounds [1 x %struct.__va_list_tag], ptr %[[ARGS]], i64 0, i64 0
+// OGCG:   call void @llvm.va_end.p0(ptr %[[ARRDECAY2]])
+// OGCG:   ret void

llvmbot · 2025-08-15T15:19:46Z

@llvm/pr-subscribers-clang

Author: Morris Hafner (mmha)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/153819.diff

8 Files Affected:

(modified) clang/include/clang/CIR/Dialect/IR/CIROps.td (+77)
(modified) clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp (+21)
(modified) clang/lib/CIR/CodeGen/CIRGenExpr.cpp (+2-5)
(modified) clang/lib/CIR/CodeGen/CIRGenFunction.cpp (+6)
(modified) clang/lib/CIR/CodeGen/CIRGenFunction.h (+13)
(modified) clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp (+22)
(modified) clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h (+20)
(added) clang/test/CIR/CodeGen/var_arg.c (+48)

diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index a77e9199cdc96..86c8b59bf36f0 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -3415,4 +3415,81 @@ def CIR_FAbsOp : CIR_UnaryFPToFPBuiltinOp<"fabs", "FAbsOp"> {
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// Variadic Operations
+//===----------------------------------------------------------------------===//
+
+def CIR_VAStartOp : CIR_Op<"va.start"> {
+  let summary = "Starts a variable argument list";
+  let description = [{
+    The cir.va.start operation models the C/C++ va_start macro by
+    initializing a variable argument list at the given va_list storage
+    location.
+
+    The operand must be a pointer to the target's `va_list` representation.
+    This operation has no results and produces its effect by mutating the
+    storage referenced by the pointer operand.
+
+    Each `cir.va.start` must be paired with a corresponding `cir.va.end`
+    on the same logical `va_list` object along all control-flow paths. After
+    `cir.va.end`, the `va_list` must not be accessed unless reinitialized
+    with another `cir.va.start`.
+
+    Lowering typically maps this to the LLVM intrinsic `llvm.va_start`,
+    passing the appropriately decayed pointer to the underlying `va_list`
+    storage.
+
+    Example:
+
+    ```mlir
+    // %args : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>
+    %p = cir.cast(array_to_ptrdecay, %args
+          : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>),
+        !cir.ptr<!rec___va_list_tag>
+    cir.va.start %p : !cir.ptr<!rec___va_list_tag>
+    ```
+  }];
+  let arguments = (ins CIR_PointerType:$arg_list);
+
+  let assemblyFormat = [{
+    $arg_list attr-dict `:` type(operands)
+  }];
+}
+
+def CIR_VAEndOp : CIR_Op<"va.end"> {
+  let summary = "Ends a variable argument list";
+  let description = [{
+    The `cir.va.end` operation models the C/C++ va_end macro by finalizing
+    and cleaning up a variable argument list previously initialized with
+    `cir.va.start`.
+
+    The operand must be a pointer to the target's `va_list` representation.
+    This operation has no results and produces its effect by mutating the
+    storage referenced by the pointer operand.
+
+    `cir.va.end` must only be called after a matching `cir.va.start` on the
+    same `va_list` along all control-flow paths. After `cir.va.end`, the
+    `va_list` is invalid and must not be accessed unless reinitialized.
+
+    Lowering typically maps this to the LLVM intrinsic `llvm.va_end`,
+    passing the appropriately decayed pointer to the underlying `va_list`
+    storage.
+
+    Example:
+    ```mlir
+    // %args : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>
+    %p = cir.cast(array_to_ptrdecay, %args
+          : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>),
+        !cir.ptr<!rec___va_list_tag>
+    cir.va.end %p : !cir.ptr<!rec___va_list_tag>
+    ```
+  }];
+
+  let arguments = (ins CIR_PointerType:$arg_list);
+
+  let assemblyFormat = [{
+    $arg_list attr-dict `:` type(operands)
+  }];
+}
+
 #endif // CLANG_CIR_DIALECT_IR_CIROPS_TD
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 36aea4c1d39ce..25ca10e801194 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -125,6 +125,18 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
   default:
     break;
 
+  // C stdarg builtins.
+  case Builtin::BI__builtin_stdarg_start:
+  case Builtin::BI__builtin_va_start:
+  case Builtin::BI__va_start:
+  case Builtin::BI__builtin_va_end: {
+    emitVAStartEnd(builtinID == Builtin::BI__va_start
+                       ? emitScalarExpr(e->getArg(0))
+                       : emitVAListRef(e->getArg(0)).getPointer(),
+                   builtinID != Builtin::BI__builtin_va_end);
+    return {};
+  }
+
   case Builtin::BIfabs:
   case Builtin::BIfabsf:
   case Builtin::BIfabsl:
@@ -361,3 +373,12 @@ mlir::Value CIRGenFunction::emitCheckedArgForAssume(const Expr *e) {
                "emitCheckedArgForAssume: sanitizers are NYI");
   return {};
 }
+
+void CIRGenFunction::emitVAStartEnd(mlir::Value argValue, bool isStart) {
+  // LLVM codegen casts to *i8, no real gain on doing this for CIRGen this
+  // early, defer to LLVM lowering.
+  if (isStart)
+    cir::VAStartOp::create(builder, argValue.getLoc(), argValue);
+  else
+    cir::VAEndOp::create(builder, argValue.getLoc(), argValue);
+}
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
index 8bcca6f5d1803..00f2a64281b8c 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -90,11 +90,8 @@ Address CIRGenFunction::emitPointerWithAlignment(const Expr *expr,
     } break;
 
     // Array-to-pointer decay. TODO(cir): BaseInfo and TBAAInfo.
-    case CK_ArrayToPointerDecay: {
-      cgm.errorNYI(expr->getSourceRange(),
-                   "emitPointerWithAlignment: array-to-pointer decay");
-      return Address::invalid();
-    }
+    case CK_ArrayToPointerDecay:
+      return emitArrayToPointerDecay(ce->getSubExpr());
 
     case CK_UncheckedDerivedToBase:
     case CK_DerivedToBase: {
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.cpp b/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
index d6a0792292604..917afa8e78021 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.cpp
@@ -1080,4 +1080,10 @@ void CIRGenFunction::emitVariablyModifiedType(QualType type) {
   } while (type->isVariablyModifiedType());
 }
 
+Address CIRGenFunction::emitVAListRef(const Expr *e) {
+  if (getContext().getBuiltinVaListType()->isArrayType())
+    return emitPointerWithAlignment(e);
+  return emitLValue(e).getAddress();
+}
+
 } // namespace clang::CIRGen
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
index 9a887ec047f86..1c89c2c9d57d3 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.h
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -1411,6 +1411,19 @@ class CIRGenFunction : public CIRGenTypeCache {
                                     const clang::Stmt *thenS,
                                     const clang::Stmt *elseS);
 
+  /// Build a "reference" to a va_list; this is either the address or the value
+  /// of the expression, depending on how va_list is defined.
+  Address emitVAListRef(const Expr *e);
+
+  /// Emits a CIR variable-argument operation, either
+  /// \c cir.va.start or \c cir.va.end.
+  ///
+  /// \param argValue A reference to the \c va_list as emitted by either
+  /// \c emitVAListRef or \c emitMSVAListRef.
+  ///
+  /// \param isStart If \c true, emits \c cir.va.start, otherwise \c cir.va.end.
+  void emitVAStartEnd(mlir::Value argValue, bool isStart);
+
   /// ----------------------
   /// CIR build helpers
   /// -----------------
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index 1ea296a6887ef..e51fbc9eadaf0 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -2336,6 +2336,8 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                CIRToLLVMTrapOpLowering,
                CIRToLLVMUnaryOpLowering,
                CIRToLLVMUnreachableOpLowering,
+               CIRToLLVMVAEndOpLowering,
+               CIRToLLVMVAStartOpLowering,
                CIRToLLVMVecCmpOpLowering,
                CIRToLLVMVecCreateOpLowering,
                CIRToLLVMVecExtractOpLowering,
@@ -3035,6 +3037,26 @@ mlir::LogicalResult CIRToLLVMInlineAsmOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+mlir::LogicalResult CIRToLLVMVAStartOpLowering::matchAndRewrite(
+    cir::VAStartOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto opaquePtr = mlir::LLVM::LLVMPointerType::get(getContext());
+  auto vaList = mlir::LLVM::BitcastOp::create(rewriter, op.getLoc(), opaquePtr,
+                                              adaptor.getArgList());
+  rewriter.replaceOpWithNewOp<mlir::LLVM::VaStartOp>(op, vaList);
+  return mlir::success();
+}
+
+mlir::LogicalResult CIRToLLVMVAEndOpLowering::matchAndRewrite(
+    cir::VAEndOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto opaquePtr = mlir::LLVM::LLVMPointerType::get(getContext());
+  auto vaList = mlir::LLVM::BitcastOp::create(rewriter, op.getLoc(), opaquePtr,
+                                              adaptor.getArgList());
+  rewriter.replaceOpWithNewOp<mlir::LLVM::VaEndOp>(op, vaList);
+  return mlir::success();
+}
+
 std::unique_ptr<mlir::Pass> createConvertCIRToLLVMPass() {
   return std::make_unique<ConvertCIRToLLVMPass>();
 }
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
index e32bf2d1bae0c..72315ac127e1b 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
@@ -684,6 +684,26 @@ class CIRToLLVMInlineAsmOpLowering
                   mlir::ConversionPatternRewriter &) const override;
 };
 
+class CIRToLLVMVAStartOpLowering
+    : public mlir::OpConversionPattern<cir::VAStartOp> {
+public:
+  using mlir::OpConversionPattern<cir::VAStartOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::VAStartOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
+class CIRToLLVMVAEndOpLowering
+    : public mlir::OpConversionPattern<cir::VAEndOp> {
+public:
+  using mlir::OpConversionPattern<cir::VAEndOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::VAEndOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
 } // namespace direct
 } // namespace cir
 
diff --git a/clang/test/CIR/CodeGen/var_arg.c b/clang/test/CIR/CodeGen/var_arg.c
new file mode 100644
index 0000000000000..7cd10e1ca42d2
--- /dev/null
+++ b/clang/test/CIR/CodeGen/var_arg.c
@@ -0,0 +1,48 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -Wno-unused-value -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+void varargs(int count, ...) {
+    __builtin_va_list args;
+    __builtin_va_start(args, 12345);
+    __builtin_va_end(args);
+}
+
+// CIR: !rec___va_list_tag = !cir.record<struct "__va_list_tag" {!u32i, !u32i, !cir.ptr<!void>, !cir.ptr<!void>}
+
+// CIR: cir.func dso_local @varargs(%[[COUNT_ARG:.+]]: !s32i {{.*}}, ...) {{.*}}
+// CIR:   %[[COUNT:.+]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["count", init]
+// CIR:   %[[ARGS:.+]]  = cir.alloca !cir.array<!rec___va_list_tag x 1>, !cir.ptr<!cir.array<!rec___va_list_tag x 1>>, ["args"]
+// CIR:   cir.store %[[COUNT_ARG]], %[[COUNT]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[ARGS_DECAY1:.+]] = cir.cast(array_to_ptrdecay, %[[ARGS]] : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>), !cir.ptr<!rec___va_list_tag>
+// CIR:   cir.va.start %[[ARGS_DECAY1]] : !cir.ptr<!rec___va_list_tag>
+// CIR:   %[[ARGS_DECAY2:.+]] = cir.cast(array_to_ptrdecay, %[[ARGS]] : !cir.ptr<!cir.array<!rec___va_list_tag x 1>>), !cir.ptr<!rec___va_list_tag>
+// CIR:   cir.va.end %[[ARGS_DECAY2]] : !cir.ptr<!rec___va_list_tag>
+// CIR:   cir.return
+
+// LLVM: %struct.__va_list_tag = type { i32, i32, ptr, ptr }
+
+// LLVM: define dso_local void @varargs(i32 %[[ARG0:.+]], ...)
+// LLVM:   %[[COUNT_ADDR:.+]] = alloca i32, i64 1
+// LLVM:   %[[ARGS:.+]] = alloca [1 x %struct.__va_list_tag], i64 1
+// LLVM:   store i32 %[[ARG0]], ptr %[[COUNT_ADDR]]
+// LLVM:   %[[GEP1:.+]] = getelementptr %struct.__va_list_tag, ptr %[[ARGS]], i32 0
+// LLVM:   call void @llvm.va_start.p0(ptr %[[GEP1]])
+// LLVM:   %[[GEP2:.+]] = getelementptr %struct.__va_list_tag, ptr %[[ARGS]], i32 0
+// LLVM:   call void @llvm.va_end.p0(ptr %[[GEP2]])
+// LLVM:   ret void
+
+// OGCG: %struct.__va_list_tag = type { i32, i32, ptr, ptr }
+
+// OGCG: define dso_local void @varargs(i32 noundef %[[COUNT:.+]], ...)
+// OGCG:   %[[COUNT_ADDR:.+]] = alloca i32
+// OGCG:   %[[ARGS:.+]] = alloca [1 x %struct.__va_list_tag]
+// OGCG:   store i32 %[[COUNT]], ptr %[[COUNT_ADDR]]
+// OGCG:   %[[ARRDECAY1:.+]] = getelementptr inbounds [1 x %struct.__va_list_tag], ptr %[[ARGS]], i64 0, i64 0
+// OGCG:   call void @llvm.va_start.p0(ptr %[[ARRDECAY1]])
+// OGCG:   %[[ARRDECAY2:.+]] = getelementptr inbounds [1 x %struct.__va_list_tag], ptr %[[ARGS]], i64 0, i64 0
+// OGCG:   call void @llvm.va_end.p0(ptr %[[ARRDECAY2]])
+// OGCG:   ret void

mmha · 2025-08-15T15:21:22Z

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

+    cir.va.start %p : !cir.ptr<!rec___va_list_tag>
+    ```
+  }];
+  let arguments = (ins CIR_PointerType:$arg_list);


@bcardosolopes I assumecir.va.start drops the length info from the builtin because the LLVM intrinsic does, but I think it would be useful to retain it in CIR for static code analysis purposes. What's your opinion?

I'm down for retaining it!

andykaylor

This looks good. I have just a few nits.

andykaylor · 2025-08-15T18:53:38Z

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

+    `cir.va.end`, the `va_list` must not be accessed unless reinitialized
+    with another `cir.va.start`.
+
+    Lowering typically maps this to the LLVM intrinsic `llvm.va_start`,


Typically? Are there cases where it doesn't?

I remember some issues with va_arg (where OG might not lower to the LLVM intrinsic - llvm/clangir#862), I'm not sure about va.start though.

My mind was at "What if we don't lower to LLVM?". I removed the "typically".

The LLVM intrinsic has a few problems because it's not a complete solution and sometimes generates worse code which is why classic codegen only uses it as a default in its ABI lowering. See here or here.

In #153834 I added lowering to llvm.va_arg as a default in LowerToLLVM. Once we get proper ABI lowering in LoweringPrepare (or at a similar stage) upstream a target can replace cir.va_arg with something else. But for now this is a good stopgap to enable things like scalar varargs on most platforms.

sounds good to me

andykaylor · 2025-08-15T18:57:15Z

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

-      return Address::invalid();
-    }
+    case CK_ArrayToPointerDecay:
+      return emitArrayToPointerDecay(ce->getSubExpr());


Can you add the baseinfo argument and insert a missing feature asserts here for tbaa?

andykaylor · 2025-08-15T19:07:05Z

clang/test/CIR/CodeGen/var_arg.c

+
+void varargs(int count, ...) {
+    __builtin_va_list args;
+    __builtin_va_start(args, 12345);


Can you add test cases that use Builtin::BI__builtin_stdarg_start and Builtin::BI__va_start? (Assuming this one corresponds to Builtin::BI__builtin_va_start)

bcardosolopes

LGTM, nothing to add on top of Andy's comments

bcardosolopes · 2025-08-15T22:01:28Z

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

+    cir.va.start %p : !cir.ptr<!rec___va_list_tag>
+    ```
+  }];
+  let arguments = (ins CIR_PointerType:$arg_list);


I'm down for retaining it!

Retain count parameter add baseInfo arg and add tbaa missing feature Add test

mmha · 2025-08-18T12:15:27Z

I changed the op definition to keep the count in CIR. So I'm asking for a small re-review :)

It leads to somewhat worse LLVM IR because of a dead load but I don't think there's much we can do here.

bcardosolopes

Changes LGTM, thanks

This patch fixes a regression introduced by llvm#153819. The evaluation order of the arguments to `emitVAStart` is unspecified, but the test requires the arguments to be evaluated in left-to-right order.

This patch fixes a regression introduced by #153819. The evaluation order of the arguments to `emitVAStart` is unspecified, but the test requires the arguments to be evaluated in left-to-right order. It's a bit strange that the pre-merge checks did not catch this. The tests failed on my local machine, which runs Fedora 42 with gcc 15.2.1 .

Part of llvm#153286. Depends on llvm#153819. This patch adds support for __builtin_va_arg by adding the cir.va.arg operator. Unlike the incubator it doesn't depend on any target specific lowering (yet) but maps to llvm.va_arg.

Part of #153286. Depends on #153819. This patch adds support for __builtin_va_arg by adding the cir.va.arg operator. Unlike the incubator it doesn't depend on any target specific lowering (yet) but maps to llvm.va_arg.

Part of llvm/llvm-project#153286. Depends on llvm/llvm-project#153819. This patch adds support for __builtin_va_arg by adding the cir.va.arg operator. Unlike the incubator it doesn't depend on any target specific lowering (yet) but maps to llvm.va_arg.

[CIR] Upstream __builtin_va_start and __builtin_va_end

dae7b97

mmha requested review from andykaylor, bcardosolopes, lanza and xlauko as code owners August 15, 2025 15:19

llvmbot added clang Clang issues not falling into any other category ClangIR Anything related to the ClangIR project labels Aug 15, 2025

mmha commented Aug 15, 2025

View reviewed changes

mmha mentioned this pull request Aug 15, 2025

[CIR] Implement__builtin_va_arg #153834

Merged

andykaylor approved these changes Aug 15, 2025

View reviewed changes

bcardosolopes approved these changes Aug 15, 2025

View reviewed changes

cir.va.start/end -> cir.va_start/end

df15b9b

Retain count parameter add baseInfo arg and add tbaa missing feature Add test

mmha requested review from andykaylor and bcardosolopes August 18, 2025 12:01

bcardosolopes approved these changes Aug 19, 2025

View reviewed changes

mmha merged commit b44e47a into llvm:main Aug 19, 2025
9 checks passed

Lancern mentioned this pull request Aug 19, 2025

[CIR][NFC] Fix regression by #153819 #154346

Merged

[CIR] Upstream __builtin_va_start and __builtin_va_end #153819

[CIR] Upstream __builtin_va_start and __builtin_va_end #153819

Uh oh!

Conversation

mmha commented Aug 15, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

llvmbot commented Aug 15, 2025

Uh oh!

llvmbot commented Aug 15, 2025

Uh oh!

mmha Aug 15, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

andykaylor left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

bcardosolopes left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

mmha commented Aug 18, 2025

Uh oh!

bcardosolopes left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

mmha commented Aug 15, 2025 •

edited

Loading

mmha Aug 15, 2025 •

edited

Loading